To see the other types of publications on this topic, follow the link: Microphytobentho.
Dissertations / Theses on the topic 'Microphytobentho'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Microphytobentho.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Coelho, Helena Isabel Soares Dinis. "Microphytobenthos vs Hydrobia: trophic coupling in estuarine environment." Doctoral thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/3632.
Full textAbstract:
Doutoramento em BiologiaOs estuários são ambientes complexos, biologicamente diversos e muito importantes no que respeita à produtividade primária. As zonas intertidais destes ecossistemas são ocupadas por organismos que possuem uma elevada capacidade de sobrevivência e adaptação face às variadas e rápidas alterações nos factores ambientais (tais como temperatura, salinidade, conteúdo hídrico, etc.). As cadeias tróficas com origem no ecossistema estuarino bentónico são essencialmente herbívoras, regulando o fluxo de energia desde o fundo sedimentar e através do ecossistema. Nas áreas estuarinas intertidais a produção primária é essencialmente suportada pelo microfitobentos (MPB). Estas comunidades de microalgas bênticas constituem uma importante fonte de matéria orgânica e são por si só a principal fonte alimentar para as populações de Hydrobia. Neste contexto, a interacção MPB - Hydrobia é um modelo-chave na investigação da cadeia trófica estuarina de origem bentónica, actuando como um importante canal de transporte de energia para os níveis tróficos superiores, especialmente se considerarmos que Hydrobia é uma importante presa para peixes, aves e caranguejos. O presente estudo tem por objectivos gerais: i) a investigação do controlo ambiental (particularmente da luz e do teor em água do sedimento) e endógeno na migração vertical do MPB e ii) a identificação e potencial utilização de marcadores tróficos (pigmentos e ácidos gordos) úteis à investigação da interacção MPB – Hydrobia em laboratório e em condições naturais, considerando a existência de uma elevada plasticidade trófica por parte da Hydrobia e a elevada densidade populacional que estes organismos podem apresentar. A primeira fase de investigação resultou na comparação do papel dos estímulos ambientais e do controlo endógeno nos padrões de comportamento migratório vertical do microfitobentos, demonstrando a existência de um controlo essencialmente endógeno na formação e desintegração do biofilme superficial. A regulação e manutenção da biomassa à superfície do sedimento são claramente controladas pela variação dos factores ambientais, em especial da luz, cuja presença é essencial à formação total do biofilme microalgal à superfície do sedimento intertidal. Foi proposta uma nova abordagem metodológica com vista à estimativa nãodestrutiva do teor de água de sedimentos intertidais vasosos , possibilitando o estudo da influência da acção do vento no conteúdo hídrico dos sedimentos e o consequente impacto da dessecação na comunidade microfitobêntica. Observou-se que a dessecação provoca efeitos limitantes não só na biomassa superficial mas também na actividade fotossintética dos biofilmes microfitobênticos, conduzindo à diminuição da produtividade primária. No que respeita à dinâmica trófica da interacção MPB - Hydrobia foi estabelecido o uso do pigmento feoforbide a, quantificado nas partículas fecais da fauna, como marcador trófico que permite estimar a quantidade de biomassa de microalgas (clorofila a) incorporada pelos organismos animais.Para tal foi investigada e comprovada a existência de uma relação significativa entre a concentração de feopigmentos excretados e a concentração de clorofila a ingerida. Estes estudos foram desenvolvidos numa primeira fase à escala diária, considerando os efeitos dos ciclos sazonais, dia-noite e maré, e depois com a validação em condições naturais, numa escala mensal. A taxa de ingestão média de indivíduos de H. ulvae varia ao longo do dia, com o máximo em torno dos períodos diurnos de maré baixa, o que pode estar relacionado com a disponibilidade de MPB. As taxas de ingestão (TI) de H. ulvae variam ainda em função da estação do ano (TI verão > TI primavera) e em função da densidade de indivíduos (> densidade, < ingestão). Verificou-se um efeito negativo na concentração de clorofila disponível após herbívoria independentemente da densidade de indivíduos. Finalmente, a comparação dos perfis de ácidos gordos de H. ulvae provenientes de diferentes habitats com os perfis de potenciais fontes alimentares permitiu demonstrar que os ácidos gordos são ferramentas úteis na identificação do habitat ocupado por estes organismos. No entanto, apesar da ocupação de diferentes habitats e da integração de múltiplas fontes de produção primária na sua dieta foram sempre observados significativos níveis de ácidos gordos específicos de microalgas (em particular diatomáceas), reforçando o papel importante das comunidades de microalgas bênticas na dieta das populações de H. ulvae.
Estuaries are biologically diverse and form complex environments, which play an important role on the global primary productivity of aquatic environments. Intertidal areas of estuaries are inhabited by organisms with a strikingly capability to survive and to be adapted to frequent and fast changes in several environmental factors (such as temperature, salinity, water content, etc.). Grazing food chains are common in intertidal mudflats regulating the flow of nutrients and energy from the bottom throughout the estuarine ecosystem. Within intertidal estuarine areas the primary production was predominantly supported by microphytobenthos (MPB). These benthic microalgae assemblages are an important source of organic matter and are a main food source for Hydrobia populations. The MPB - Hydrobia interaction is a key model for the estuarine grazing food chain, acting as a significantly channel of energy to higher trophic levels, since Hydrobia is an important prey item for fish, birds and crabs. The present work addressed: i) the environmental (namely light and sediment water content) and the endogenous control of the vertical migration by microphytobenthos, and ii) the identification and the potential use of trophic markers (pigments and fatty acids) to establish this relationship under laboratory and natural conditions, considering that H. ulvae showed significant trophic plasticity and that mud snails could reach extremely high densities. The role of exogenous cues and endogenous control of the patterns of vertical migratory behavior of intertidal MPB biofilms were compared, showing that the formation and disintegration of the biofilm is endogenously-controlled. The regulation and maintenance of the microalgal biomass at the sediment surface is dependent on the variation of environmental factors, namely light, which is essential for the full formation of the MPB biofilm. A new methodological approach was proposed to estimate the water content of muddy intertidal sediments, enabling the study of the influence of wind on the hydric level of the sediment and the consequent impact of desiccation on the MPB biomass. This investigation showed that desiccation might be responsible to cause important limiting effects on biomass and photosynthetic activity of intertidal MPB biofilms, reducing the primary productivity. Regarding the trophic dynamics of the interaction MPB - Hydrobia, it was established the use of the pigment pheophorbide a, present on Hydrobia ulvae faecal pellets, as a trophic marker to estimate the amount of microalgal biomass incorporated, as chlorophyll a, by benthic macrofauna. A significant relationship between egested pheopigments and ingested chlorophyll a was investigated and validated. These studies were firstly developed on a daily scale, considering the effects of seasonal, tidal and day-night cycles, followed by a validation under natural conditions, on a monthly scale. The mean ingestion rate of H. ulvae individuals varied along the day, with the maximum around the diurnal low tide periods, which may be related with MPB availability. H. ulvae mean ingestion rate (IR) also varies seasonally (IR summer > IR spring) and depending on mud snails density (> density, < ingestion). There was a negative effect on chlorophyll concentration available after grazing, independently of H. ulvae density. Finally, the comparison of fatty acid profiles of mud snails from different habitats with the ones from potential food sources allowed identifying fatty acids as a useful tool to indicate H. ulvae habitat. Although the occupation of different habitats and the integration of multiple primary food sources on mud snails diet, significant inputs of fatty acids specific of microalgae (namely diatoms) were always found, which reinforce the important role of MPB on the diet of H. ulvae populations.
FCT; FSE - SFRH/BD/23720/2005
2
Consalvey, Mireille. "The structure and function of microphytobenthic biofilms." Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/2682.
Full textAbstract:
Microphytobenthos are the dominant primary producers on estuarine mudflats playing a key role in the functioning of the ecosystem. Studies into microphytobenthic ecology have previously been limited by scale but the advent of fine scale analysis techniques (gm) as well as non-destructive sampling has enabled the system to be examined at a level not previously possible. This study examined the formation, structure and function of microphytobenthic biofilms using non-destructive (remote sensing by PAM fluorescence; fibreoptic light microprofiling) and destructive (cryo-freezing and Low temperature scanning electron microscopy) sampling. Many microphytobenthic organisms are motile and have evolved complex migratory strategies. Microphytobenthic migratory patterns are widely described but much remains to be elucidated about the controlling factors. The fluorescence parameter F015 (minimum fluorescence yield after 15 minutes dark adaptation) was used to monitor short-term changes in biomass at the sediment surface. Light, tidal state, endogeny and combinations thereof were all shown to control migration, demonstrating that predictable migratory rhythms cannot be assumed. Microscale sectioning showed that chlorophyll a was always concentrated in the top 400 gm (the photosynthetically active biomass). Clear migratory patterns were not detected using microscale sectioning therefore indicating that migration occurs over a scale < 400gm. Despite no changes in the chlorophyll a content in the surface layers, LTSEM analysis demonstrated diurnal taxonomic shifts providing circumstantial evidence that microphytobenthic cells sub-cycle at the sediment surface to optimise fitness. The light extinction co-efficient (k) of microphytobenthic biofilms significantly vaned with site, assemblage and also over time. 90% of the surface PPFD had always been attenuated by 400, and in many cases before 200. Traditional microphytobenthic primary productivity models do not account for changes in the spatial and temporal distribution of biomass or light attenuation and therefore their applicability to the real situation may be limited.
3
Ginnever, Naomi Elizabeth. "The photophysiology of rocky intertidal microphytobenthic biofilms." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/59459/.
Full textAbstract:
Rocky shore microphytobenthic biofilms are areas of high biodiversity, and are protected under UK and European Union legislation. Despite this, little is known about the photophysiology of these biofilms. This study aimed to provide a new contribution to microphytobenthic research with the addition of photophysiological knowledge focussing on the rocky intertidal to add to the extensive photophysiological research which has focussed on mudflats. More specifically the photoregulatory mechanisms of rocky shore biofilms had not been studied prior to this work. This study aimed to determine the effects of ambient environmental conditions, community structure and grazing on the photophysiology of the biofilms and elucidate the complex relationships between the abiotic and biotic factors which influence the biofilm. The community structure of the biofilm changed seasonally, with larger species (> 40 μm valve length and > 25 μm diameter) such as Parlibellus delognei being dominant during the winter months (December, January and February) and smaller ones (<40 μm valve length and < 25 μm diameter) such as Navicula bottnica during the spring months (March, April and May) indicating an environmental influence on the community structure of the biofilm. The biofilms were found to die-off (biomass below detection levels) in April and May and grow back in the November and December during a ‘reproductive phase’. An observed photophysiological ‘seasonality’ was primarily the result of the timing of the‘reproductive phase’ of the biofilm, with higher maximum relative electron transport rates (rETRmax) being recorded during November and December (on average 85 compared to 60 relative units), when these biofilms were growing after the spring die-off. High temperature and light dose had a negative effect on the rETRmax, particularly for biofilms on the upper shore sites. It was concluded that the combination of increased temperature and light dose, reducing rETRmax, and so productivity, and increased grazing contributed significantly to the spring dieoff with cells unable to replicate rapidly enough to compensate for increased grazing. By exposing biofilms to different temperatures ex-situ it was found that the lower shore biofilms ii were more resilient to high (> 25 °C) and low (< 10 °C) temperature with a smaller reduction in rETRmax, and ΔF/Fm’ observed in comparison to upper shore. Temperature was found to induce movement in the tube-forming upper shore species Navicula bottnica. This was likely to act as a secondary photoregulation strategy as it was found that high temperatures resulted in a reduced ability to induce non-photochemical quenching (NPQ). Biofilms were also treated with Latrunculin A (LAT-A) and DL- Dithiothreitol (DTT) in situ, and by comparing the photosynthetic patterns of response over an exposure period it was found that the upper shore biofilms utilised NPQ as the primary means of photoregulation whereas the lower shore biofilms utilised cell movement as the primary photoregulatory mechanisms. The upper and lower shore biofilms also utilised secondary mechanisms, migration in the upper shore samples, and NPQ in the lower shore samples, of downregulation, which allowed the cells to persist on the rocky shore where the rapid changes in environmental conditions result in a high stress environment. The overarching conclusion from this study is that rocky shore biofilms utilise a combination of photoregulatory mechanisms dependent upon life form in order to survive in an environment where many rapidly changing biotic and abiotic factors affect the community structure and photosynthesis of the biofilms.
4
Larson, Fredrik R. M. "The role of marine microphytobenthos with emphasis of resilience /." Göteborg : Göteborg University, Department of Marine Ecology, 2005. http://www.gbv.de/dms/goettingen/505476940.pdf.
Full text
5
Weinmann, Birgit Ellen. "Microphytobenthic diversity and function in estuarine soft sediment." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3664.
Full textAbstract:
Corophium volutator (Pallas) fit the criteria of ‘ecosystem engineers' as defined by Jones and colleagues (1994, 1997): they are widely distributed within and across North Atlantic estuaries, are often present in intertidal soft sediment in vast numbers, and build semi-permanent burrows in the sediment matrix, which they irrigate continuously. Previous studies have demonstrated that C. volutator burrowing and feeding not only modifies the sediment biogeochemistry but can also modify the overlying water biogeochemistry (during immersion). C. volutator activities have also been shown to be detrimental to microphytobenthic (MPB) biofilms in the immediate vicinity of the burrows. As MPB are the stabilizing force in the estuary, the decimation of biofilm destabilizes the habitat for all the organisms colonising it. However, several aspects of C. volutator ecology remain unclear. First, previous studies on the effect of C. volutator on local (within burrow proximity) MPB diversity have not presented a clear signal as to whether they increase or decrease biodiversity or established whether there is preferential survival amongst MPB taxa with certain cell shapes and sizes or lifestyles. Second, as it has been established that C. volutator have the potential to change the water column, it is possible for them to effect MPB populations remotely (outwith burrow proximity). It is therefore of interest to determine the effects they have, whether such an effect can be achieved within a tidal period, and whether these effects can change MPB biomass, behaviour or diversity over time. A series of controlled mesocosm experiments were carried out to quantify those effects of C. volutator on the water column which were likely to impact MPB survival, to determine whether those effects were specific to C. volutator or common to deposit‐feeding bioturbators, to determine to what degree they could be achieved within a single immersion period, and to separate the effects of C. volutator on MPB bulk (chlorophyll-a in top 5 mm) and photosynthesizing (fluorescing) biomass and diversity both ‘locally' and ‘remotely'. The results of the first 3 experiments consistently showed that C. volutator substantially increased the resuspension of sediment to the overlying water column and that the resulting turbidity could reduce lightpenetration to the sediment by as much as 50% within one immersion period. Results of nutrient fluxes were less consistent and clear within and between experiments but there was some suggestion that increased bioirrigation increased inorganic nitrogen flux to the overlying water column in accordance with previous studies. The effects of C. volutator on local and remote MPB biomass (bulk and surface) and diversity varied between experiments but, broadly speaking: (1) bulk biomass was unaffected, reduced locally, or increased remotely; (2) surface biomass was reduced both locally and remotely; and (3) community diversity (Simpson's diversity index) was consistently unaffected, both locally and remotely. Because increased water column turbidity is the most distinctive calling card of C. volutator but is only likely to affect the photosynthetically active (surface) MPB biomass during immersion, a controlled laboratory experiment was designed to examine the extent to which turbidity could influence MPB migratory behaviour and photosynthetic activity. MPB bulk migration was shown to be driven by sitespecific, entrained rhythms of light availability and spatial variation in light availability only drove micro‐cycling in the photic zone during the immersion period. So, in the absence of C. volutator, or any other turbidity producing phenomenon (deep water columns, high flow rates, physical disturbance, etc.), MPB will remain at the surface to photosynthesize during immersion and the productivity during this period is determined by total light intensity and exposure hours (or ‘light dose'). Therefore, the proximity and size of C. volutator populations to a site is likely to be influential in determining local productivity patterns of MPB. In addition, differences in MPB assemblage composition were shown to influence the biofilm productivity but what drives changes in MPB assemblage composition is still unclear and requires further investigation.
6
Allison, Jeffrey Garner. "Dynamics of estuarine microphytobenthos in a shallow water sand bottom habitat." [Pensacola, Fla.] : University of West Florida, 2006. http://purl.fcla.edu/fcla/etd/WFE0000004.
Full text
7
Facca, Chiara. "Phytoplancton et microphytobenthos comme indicateurs de l'état trophique en milieu côtier." Montpellier 2, 2003. http://www.theses.fr/2003MON20148.
Full text
8
Boulcott, Mat. "The dynamics of carbohydrate production, storage and excretion in epipelic diatoms." Thesis, University of Essex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343503.
Full text
9
Morelle, Jerome. "Dynamique spatiale et temporelle de la production primaire de l'estuaire de la Seine." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMC252/document.
Full textAbstract:
Les estuaires, de par leur position stratégique à l'interface entre les eaux continentales et les eaux marines jouent un rôle écologique de première importance et sont le siège de nombreuses activités humaines. L’estuaire de Seine est caractéristique des grands estuaires anthropisés. Le management à long terme de ces écosystèmes soumis à des pressions croissantes réside notamment en une meilleure connaissance de la dynamique spatiale et temporelle des réseaux trophiques estuariens. Le phytoplancton et le microphytobenthos sont les principaux contributeurs de la production primaire (PP) dans ces écosystèmes et sont à la base des réseaux trophiques. Ces compartiments sont souvent réduits à la teneur en chlorophylle du milieu et leur productivité n’a jamais été mesurée à l’échelle de l’estuaire de Seine. L’objectif de ces travaux a été d’estimer la PP de ces compartiments le long du gradient halin. Afin d’accéder à des mesures à une haute résolution spatiale, des mesures de fluorescence modulée (PAM) à haute fréquence ont été couplées à des mesures d’incorporation de carbone (13C) à basse fréquence. Les mesures de production primaire ont été mises en perspective avec la dynamique des paramètres physico-chimiques du milieu et la structure communautés phytoplanctoniques déterminés par différentes techniques (microscopie, cytométrie, biologie moléculaire). La dynamique du carbone excrété sous forme de TEP (Transparent Exopolymeric Particules) et EPS (Exopolymeric substances) a également été étudiée pour chacun des compartiments. Au-delà des méthodologies innovantes mises en place qui montre l’intérêt des mesures à haute fréquence dans ces écosystèmes très dynamiques, ce travail apporte une nouvelle vision de la dynamique du phytoplancton et de la richesse spécifique du microbiome estuarien et apporte une estimation fiable de la production primaireThe estuaries play an important ecological role and are the site of many human activities because of their strategic position at the interface between continental and marine waters. Seine estuary is characteristic of large anthropized estuaries. Long-term management requires better knowledge of the spatial and temporal dynamics of the estuarine food webs. Phytoplankton and microphytobenthos are the main contributor of primary production (PP) in these ecosystems and are at the basis of trophic food webs. These compartments are often reduced to the chlorophyll concentration and their productivity has never been measured along the Seine estuary. The objective of this study was to estimate the PP of these compartments along the salinity gradient. In order to access to measurements at high spatial resolution, high-frequency measurements of modulated fluorescence (PAM) were coupled to low-frequency carbon (13C) incorporation measurements. The primary production measurements have been put into perspective with the dynamics of the physical and chemical parameters and the structure of phytoplankton communities determined by different techniques (microscopy, cytometry, molecular biology). The dynamics of carbon excreted as TEP (Transparent Exopolymeric Particles) and EPS (Exopolymeric substances) were also studied for each compartment. Beyond the innovative methodologies which demonstrate the interest of high-frequency measurements in these highly dynamic ecosystems, this work provides a new insight into the phytoplankton dynamics and the specific richness of the estuarine microbiome and provides a reliable estimate of primary production
10
Molesky, Thomas J. "Interactions between oyster reefs and adjacent sandflats : effects on microphytobenthos and sediment characteristics /." Electronic version (Microsoft Word), 2003. http://dl.uncw.edu/etd/2003/moleskyt/tommolesky.doc.
Full text
11
Chatterjee, Arnab. "Rôle des micro-algues benthiques dans la zone côtière : biomasse, biodiversité, productivité." Thesis, Brest, 2014. http://www.theses.fr/2014BRES0005/document.
Full textAbstract:
L'état et l'évolution des écosystèmes côtiers font partie des principales préoccupations des institutions européennes. Leur fonctionnement global et leur structure sont fortement conditionnés par le comportement des premiers échelons de la chaîne alimentaire, et en particulier par les micro-algues qui se développent dans la colonne d’eau (phytoplancton) et au niveau du sédiment (microphytobenthos).Ces microalgues constituent les plus importants producteurs primaires des zones côtières (Pannard et al., 2008 ; Woelfel et al., 2010). Ils sont à la base de la chaine trophique et composent l’essentiel de la nourriture de la faune, en particulier des espèces économiquement importantes (praires, huîtres,….). Cependant, bien que le phytoplancton ait été largement étudié, le microphytobenthos est beaucoup moins connu, en particulier dans les zones subtidales. Il colonise tous les milieux (roche, vase…) dès lors qu’il y a suffisamment de lumière pour la photosynthèse (MacIntyre et al. 1996) et sa production peut égaler, voire même dépasser, la production du phytoplancton de la colonne d’eau qui le surplombe (Underwood and kromkamp, 1999). Dans cette étude, nous avons effectué un suivi hebdomadaire en Rade de Brest (55 sorties en mer en 2011), pour étudier simultanément la dynamique saisonnière du phytoplancton et du microphyto-benthos en relation avec les paramètres environnementaux.Nos résultats montrent que la dynamique du phytoplancton et du microphytobenthos dans la zone subtidale sont tout à fait différentes l’une de l'autre. Le microphytobenthos est le premier à se développer dans la saison. Il constitue un apport important d'énergie dans l'écosystème dès le début du printemps (avec 60% de la biomasse totale jusqu'en avril) et joue donc un rôle primordial dans le démarrage de l’activité biologique benthique. Le système se déplace ensuite d'un système dominé par la biomasse benthique au début du printemps, vers un système où la biomasse pélagique prend le dessus.Ces résultats mettent en évidence l’adaptation particulière du microphytobenthos aux faibles éclairements, puisqu’il est capable de produire la même biomasse que le phytoplancton de la colonne d’eau, mais avec 10 fois moins de lumière disponible. Le broutage par les hétérotrophes peut sans doute expliquer le déclin des biomasses microalgales et la différence de dynamique saisonnière après les premières floraisons. Le manque de nutriments, et en particulier les phosphates dissous dans l’eau pourrait aussi être avancé pour expliquer la chute de la biomasse microphytobenthique début d’avril, alors que le déclin du phytoplancton dans la première semaine du mois de mai coïncide à une carence en acide silicique. L’azote inorganique dissous devient ensuite potentiellement limitant dans la colonne d'eau avec des concentrations en dessous du seuil de détection, jusqu'à la fin d'octobre. D’un point de vue taxonomique, la communauté benthique est très spécifique et totalement différente de la communauté pélagique. Nous avons pu identifier 54 espèces, exclusivement des diatomées, toutes pennées, dominées par le genre Navicula. Dans la colonne d’eau, nous avons identifié 74 espèces, parmi lesquelles 51 étaient des diatomées (essentiellement centriques), dominées par Chaetoceros sp.. Le reste était partagé entre les dinoflagellés (dominé par Gymnodium sp.) et d’autres groupes fonctionnels comme les euglena, les cryptophycées, les prasinophycées, quelques rares coccolithophoridés et des petits flagellés non identifiés.Ces résultats très novateurs ouvrent de nouvelles perspectives de recherches. Il serait par exemple très intéressant de mieux comprendre les processus d’adaptation qu’ont développés les microalgues benthiques, pour être capables à des niveaux de lumière beaucoup plus faibles, d’être aussi efficace vis-à-vis de la photosynthèse que leurs homologues pélagiques. Différentes pistes sont à l’étude comme le contenu pigmentaire ou la structure de leur enveloppe siliceuseThe most important primary producer groups of the coastal zones are suspended phytoplankton cells (Pannard et al, 2008) and microphytobenthos (MPB) (Woelfel et al., 2010). In these regions, phytoplankton and benthic microalgae are both recognized as being principal components of the diet for economically important suspension-feeding fauna (Gillespie et al., 2000). However, although phytoplankton has been vastly documented, MPB is often understudied.In sufficient light for photosynthesis they can inhabit the top few centimeters of the substrate layers (mud or sand) of marine sediment (Charpy and Charpy-Roubaud 1990, MacIntyre et al. 1996, MacIntyre and Cullen 1996) and play an important role as a food source for higher trophic levels (Revsbech et al. 1981, Sorokin 1991, Charpy and Charpy-Roubaud 1990 ). Benthic microalgal biomass mostly follows a similar distribution to the total organic matter content of surficial sediments indicating that sediment geochemical processes such as nutrient release from the breakdown of organic matter may be important in determining the distribution of MPB (Light, 1998). However, on the other hand, though not proportional with the MPB biomass, benthic production can even surpass the pelagic contribution (Underwood and kromkamp, 1999). With their ability of high primary production benthic microalgal communities can profoundly influence the flux, transformation and turnover of carbon and nutrients in coastal areas. Benthic primary producers contribute to the availability of energy and matter for benthic and pelagic food webs and define benthic and pelagic energy budgets, which affect the chemistry at the sediment-water interface, and regulate sediment stability. The shallow waters, where MPB thrives, allow a more direct interaction between pelagic and benthic processes keeping the benthos much less susceptible to physical and biochemical disturbances such as evaporation, eutrophication, and wind-forcing (Molen, 2011). Because attached microalgae can avoid advective processes and adapt to changes in light availability at short time scales, their importance is particularly enhanced (Phinney, 2004). As a result of the impact that MPB carries in a coastal ecosystem, along with the study of the functional role of MPB, investigations on their diversity have also gained some importance in the last two decades (Sundbaeck & Joensson, 1988; Blanchard, 1990; Montagna et al., 1995). Like phytoplankton, MPB communities can also act as sensitive indicators of water quality as the taxonomic composition of MPB assemblages can vary as per different nutrient levels (Lange-Bertalot, 1979; Kann, 1986). However, although the importance of MPB has been emphasized on intertidal zones (Pinckney & Zingmark, 1993; Colijn & De Jonge, 1984; Herman et al., 2000), the subtidal zones have generally been ignored till yet on this regard and as a result of which not much is known about the MPB dynamics in the subtidal zones. The subtidal zone of Bay of Brest was chosen for this study because there had been comprehensive input of nitrates to the zone in the past century .This zone has being amazingly resistant to eutrophication for quite some time, although silicate and nitrate ratio got down during the past 20 years. Research has been done previously on the spatial distribution of MPB in the zone in terms of primary productivity and biomass, but in order to achieve a more holistic view of these important photoautotrophs, a temporal study is necessary as well. The objectives of this work have been to characterize the temporal distribution of MPB in terms of biomass, productivity and biodiversity in the subtidal zone of Bay of Brest on a monthly scale, assess a comparative reasoning between MPB and the phytoplankton of the overlying water column complying on the same factors and draw an understanding on the significance of seasonal fluctuations of MPB in the overall seasonal distribution of photoautotrophs. […]
12
Dransfeld, Leonie. "The environmental and photo-physiological control of microphytobenthos primary production on an intertidal mudflat." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/42087/.
Full textAbstract:
Microphytobenthos are important primary producers on tidal flats - ecosystems which are characterised by steep physical and chemical gradients. In this study some of the environmental factors that control the distribution and primary production of benthic microalgae were investigated in a series of field surveys conducted on Hythe intertidal mudflat, Southampton Water. The ecological and photo-physiological responses of microphytobenthos to changes in physical factors were studied in the field and in controlled laboratory experiments. Results from a weekly sample program at four stations along an intertidal transect were used to address the hypothesis that changes in incident irradiance defined by a combination of meteorological factors and the tidal cycle cause significant changes in the biomass of microphytobenthos. The light regime at each station was characterised by a model which combined the changes in daylight irradiance with the timing and duration of low tide. At the low shore stations total light availability during low tide was limiting in spring and autumn/winter, when daily photo-periods ranged between 0 and 6 hours. Microalgal biomass exhibited a strong seasonality with a distinct spring bloom in April which coincided with high irradiances at spring low tide. At the high shore station which was exposed to three times longer photo-periods light availability did not correlate with microalgal biomass at any time of the year. Biomass was three times higher at this station than at the three low shore stations and showed little seasonal variation. Taxonomic marker pigments were used to describe the changes in microphytobenthos composition. High correlation between chlorophyll a and fucoxanthin on a temporal and spatial (horizontal and vertical) scale combined with taxonomic analysis gave evidence that diatoms were the main primary producers on Hythe intertidal mudflat. Chlorophyll a and Ik (defined as PBmax/ aB) correlated strongly with incident irradiance at low tide, indicating that photoadaptation of benthic microalgae was occurring. A spatial comparison of photosynthetic parameters showed that benthic microalgae inhabiting the low shore compensated for reduced photoperiods by increasing their photosynthetic capacity (PBmax) and efficiency (aB) and decreasing their Ik. Photosynthetic parameters of microphytobenthos significantly changed during the low tide period under controlled laboratory conditions, suggesting that an endogenous photosynthetic rhythm was present, which caused an increase in PBmax and ocB towards the middle of the photoperiod. Irradiance levels at low tide enhanced the short-term variation in photosynthetic parameters due to photo-adaptation. The change in rates of photosynthesis was accompanied by a significant alteration of the cellular pigment composition, as the photoprotectant xanthophyll diatoxanthin increased and diadinoxanthin decreased in proportion. Short-term changes in cellular pigment composition induced in the laboratory were greater than seasonal pigment adaptation of microphytobenthos isolated from the field. Variation of PBmaxand ocB during one photoperiod occurred on a similar scale to the seasonal and spatial changes, suggesting that short-term photo-physiological adaptations are an important feature of microphytobenthos, aiding their successful survival in the intertidal environment, where strong gradients of incident irradiance occur on small temporal and spatial scales.
13
Blanchard, Gérard. "Relations trophiques entre la méiofaune et le microphytobenthos d'un marais maritime du littoral charentais." Bordeaux 1, 1989. http://www.theses.fr/1989BOR10605.
Full textAbstract:
Les relations trophiques entre la meiofaune et le microphytobenthos ont ete etudiees au moyen de l'analyse de la microrepartition spatiale de ces communautes benthiques. Cette approche descriptive, basee sur un echantillonnage regulier et une methode originale de separation simultanee de la meiofaune et du microphytobenthos a partir du meme echantillon de sediment, a decele de nombreuses analogies entre les modeles de distribution spatiale; ce qui laisse supposer un determinisme alimentaire de la microrepartition de la meiofaune. Une verification experimentale de cette hypothese a ete effectuee par la mesure des flux de carbone entre l'echelon algal et la meiofaune. Les resultats amenent d'ailleurs a penser que la pression de broutage du meiobenthos exerce un effet stimulant sur la productivite primaire
14
Marchais, Violette. "Relations trophiques entre producteurs primaires et quatre consommateurs primaires benthiques dans un écosystème côtier tempéré." Thesis, Brest, 2014. http://www.theses.fr/2014BRES0111/document.
Full textAbstract:
Dans les zones euphotiques des écosystèmes côtiers, les producteurs primaires se développent à la fois dans l’espace pélagique (colonne d’eau) et benthique (sur ou près du fond). Dans ces écosystèmes, le couplage bentho-pélagique prend une place non négligeable qu’il convient d’étudier. Les consommateurs primaires benthiques en sont des acteurs à travers leur activité alimentaire. La relation trophique entre les différents producteurs primaires et les consommateurs primaires benthiques reste toutefois mal élucidée. Pour apporter des éléments d’informations, cette thèse s’est focalisée dans un premier temps sur la dynamique spatio-temporelle des producteurs primaires au sein de la matière organique particulaire en suspension (MOPS), notamment au niveau de l’interface eau-sédiment. Cette étude a permis de montrer une forte variation saisonnière de ce peuplement algal à toutes les profondeurs, mais également une importante contribution relative des diatomées benthiques dans la MOPS près du fond en hiver. Le second axe de recherche s’est concentré sur la relation trophique entre des consommateurs primaires benthiques (coquille Saint-Jacques, pétoncle noir, moule et ormeau) et les producteurs primaires présents dans la MOPS. L’analyse des isotopes stables dans les tissus mous des pétoncles noirs et des moules a indiqué une prédominance du phytoplancton assimilé et une potentielle contribution du microphytobenthos dans leur régime alimentaire (plus importante pour la moule), notamment en période hivernale et près du fond. Cependant, ces études ont mis en lumière l’effet du métabolisme sur les valeurs isotopiques dans les tissus mous. Un aspect novateur de cette thèse a été d’utiliser les exosquelettes des coquilles Saint-Jacques et des ormeaux pour caractériser leur régime alimentaire dans le milieu naturel, afin de s’affranchir des problèmes liés à l’utilisation des isotopes stables dans les tissus mous. Des études en conditions contrôlées ont validé l’intégration des sources d’alimentation à travers le carbone métabolique dans les carbonates de la coquille Saint-Jacques et la couleur de la coquille pour l’ormeau. Des études complémentaires doivent toutefois être menées. Enfin, une dernière étude s’est focalisée sur la capacité de la coquille Saint-Jacques à mettre en suspension les particules benthiques par leurs mouvements de valvesIn coastal euphotic areas, primary producers grow both in the pelagic (water column) and in the benthic zone (in or near the sediment). In these ecosystems, benthic-pelagic coupling is an important process which must be well described. Benthic primary consumers modify this coupling through their diet. Trophic relationships between primary producers and benthic primary consumers are not thoroughly understood. To gain additional information, this thesis was focused on the spatial and temporal dynamic of primary producers in suspended particulate organic matter (SPOM), especially at water-sediment interface. This study highlighted a seasonal variation of microalgal populations at all depths, and a relative dominance of benthic diatoms in SPOM near sediment and in winter. The second objective of the thesis was focused on the trophic relationships between benthic primary consumers (great scallop, black scallop, mussel and ormer) and primary producers in SPOM. Stable isotope analysis in soft tissues of black scallops and mussels showed a predominance of assimilated phytoplankton and the potential contribution of microphytobenthos in their diet (more important for mussel), especially in winter and near the sediment. However, this study highlighted the impact of metabolism on stable isotopic values of soft tissues. An innovative aspect of this thesis was the use of exoskeleton of great scallops and ormers to characterize their diet in natural environment and thus overcome problems related to the utilization of stable isotopes in soft tissues. Experiments in controlled conditions validated food sources integration through metabolic carbon in carbonates of great scallops and shell color for ormer but complementary studies are required on mollusk shell utilization. The last part of this thesis was focused on the ability of great scallops to achieve resuspension of benthic particles by valve movements
15
Androuin, Thibault. "Ecologie trophique de l'espèce ingénieur Crepidula fornicata et implications pour le fonctionnement de son habitat." Thesis, Brest, 2018. http://www.theses.fr/2018BRES0106.
Full textAbstract:
La crépidule (Crepidula fornicata) est une espèce invasive des côtes européennes. Hermaphrodite protandre, cette espèce grégaire forme des chaines d’individus qui s’accumulent en forte densité sur les fonds. Longtemps considérée comme un envahisseur néfaste, la crépidule est aussi un ingénieur de l’écosystème, modifiant physiquement et biologiquement son habitat. Elle constitue un modèle biologique pour étudier comment les espèces invasives et ingénieurs peuvent structurer et modifier l’écosystème qu’elles colonisent. Dans le cadre de cette thèse, ces effets ont été examinés à travers le fonctionnement trophique des habitats à crépidules, en lien notamment avec la production primaire benthique. Il a été mis en évidence expérimentalement une stimulation du microphytobenthos (MPB) subtidal grâce à l’activité biologique de la crépidule. La niche trophique de C. fornicata a été redéfinie suite à la découverte de la présence de sphérules de carbonates dans ses tissus, surestimant la contribution du MPB dans son régime alimentaire. L’utilisation de différents marqueurs trophiques (pigments, acides gras, isotopes) a révélé que les jeunes individus mobiles étaient susceptibles de brouter le MPB associé au biofilm présent sur les coquilles. Les adultes sessiles, sont des filtreurs opportunistes, où la matière détritique mais aussi du MPB contribuent à leur régime alimentaire. L’analyse de différents suspensivores inféodés à cet habitat, a démontré que la crépidule n’était pas un compétiteur trophique pour des espèces commercialement importantes (pétoncle noir et huître plate) dû à leurs mécanismes de sélection trophique. À l’échelle du réseau trophique, la crépidule en très forte densité peut conduire à une homogénéisation du réseau trophique global dû à l’enrichissement en matière organique. Au contraire, un banc mort de crépidules montre une complexité trophique similaire à celle d’un banc de maërl, écosystème à forte biodiversité. Cette thèse, en plus d’avoir caractérisé le fonctionnement trophique des bancs de crépidules, montre qu’une espèce invasive, en facilitant certains compartiments biologiques (MPB, suspensivores), peut contribuer à la richesse d’un écosystème comme celui la rade de BrestThe slipper limpet (Crepidula fornicata) is an invasive species of European coasts. Protandric hermaphrodite, this gregarious species forms individuals' stacks which accumulate in high density on bottom. For a long time considered as a detrimental invader, the slipper limpet is also an ecosystem engineer, modifying its habitat both physically and biologically. It is model to study how invasive and engineer species can structure and modify the ecosystem that they colonize. In this Ph.D. thesis, these effects have been examined through the trophic functioning of habitats colonized by the slipper limpet, with a special reference to the primary benthic production. Experimental stimulation of subtidal microphytobenthos (MPB) has been demonstrated by the biological activity of the slipper limpet.The trophic niche of C. fornicata has been redefined following the discovery of the presence of carbonate spherules in its tissues, overestimating the contribution of MPB in its diet. Several trophic markers use (pigments, fatty acids, isotopes)revealed that young motile individuals were likely to graze the MPB associated to shell biofilm. Sessile adults, were likely opportunistic filter-feeders, where detritus but also MPB contribute to their trophic diet. The analysis of several filter-feeders inhabiting Crepidula beds has demonstrated that the slipper limpet was not a trophic competitor for commercially important species (black scallop and flat oyster) due to their trophic sorting mechanisms. At the food web scale, the high density of slipper limpet can lead to a homogenization of the global food web due to organic matter enrichment. Dead Crepidula bed showed trophic complexity similar to maerl bed, which is a high biodiverse ecosystem. This thesis, in addition to characterize the trophic functioning of Crepidula beds, shows that an invasive species, in facilitating different biological compartments (MPB, filter-feeders), can contribute to the ecosystem richness such as the Bay of Brest
16
Meleder-Tard, Vona. "Étude de la structure des peuplements intertidaux du microphytobenthos : apport de la télédétection visible - infrarouge." Nantes, 2003. http://www.theses.fr/2003NANT2052.
Full textAbstract:
L'objectif de cette étude est d'évaluer l'intérêt de la télédétection multispectrale (SPOT ; bandes spectrales larges et peu nombreuses) et hyperspectrale (DAIS ; bandes spectrales étroites et nombreuses) dans le domaine visible-infrarouge (entre 400 et 1000 nm), pour l'étude des peuplements du microphytobenthos d'un écosystème intertidal. La zone d'étude choisie est une baie à caractère conchylicole de la façade atlantique, la baie de Bourgneuf (47ʿN ; 2ʿW). Le microphytobenthos est composé d'organismes unicellulaires photosynthétiques vivant dans les premiers millimètres de sédiments et largement dominés en baie de Bourgneuf par les Diatomées. La télédétection visible-infrarouge permet l'étude de ces peuplements à partir de leurs caractéristiques spectrales liées à la présence de pigments et mesurées par des radiomètres de terrain et aéroportés. Toutefois, l'interprétation de ces données radiométriques nécessite une connaissance du terrain. Une étude descriptive de la structure du microphytobenthos basée sur un suivi spatial et temporel, a été mise en place durant 15 mois en baie de Bourgneuf. Il apparaît une structuration spatiale des peuplements liée à la granulométrie et à une absence de variabilité saisonnière de la biomasse. Des mesures radiométriques sont réalisées in situ et en laboratoire (cultures monospécifiques) afin d'établir un lien avec les analyses pigmentaires des organismes mesurées en Chromatographie Liquide Haute Pression (CLHP). La biomasse du microphytobenthos est alors estimée à partir des réflectances mesurées à 632 nm (bande d'absorption de la chlorophylle c) dans une gamme de valeurs allant jusqu'à 200 mg Chl a. M-2. Une cartographie du microphytobenthos a été réalisée par les calibrations de six images multispectrales (SPOT) et d'une image hyperspectrale (DAIS) à partir de ces mêmes mesures radiométriques. Ainsi, il apparaît que les peuplements du microphytobenthos se développent le long d'une bande orientée nord-sud en bas d'estran, au niveau de l'isobathe +2 m et pouvant occuper jusqu'à 25 % de la surface étudiée. La calibration de l'image DAIS permet de bien différentier les microalgues des macroalgues. Les plus fortes biomasses microphytobenthiques cartographiées à partir de cette image sont de l'ordre de 60 mg Chl a. M-2 pour des pixels de 5x5 mThe aim of this work is to assess the use of multispectral (SPOT ; few large spectral bands) and hyperspectral (DAIS ; many thin spectral bands) visible infrared remote sensing (between 400 and 1000 nm) to study microphytobenthos assemblages in intertidal ecosystems. The study area is a shellfish ecosystem located south of the Loire river, the Bourgneuf bay (47ʿN ; 2ʿW). Microphytobenthos, which is composed of photosynthetic unicellular organisms inhabiting the upper millimetres of intertidal sediments, is dominated by Diatom in Bourgneuf bay. Each pigment of these organisms exhibit absorbance signature allowing the detection of benthic diatom biofilms by field or satellite/airborne swas around 60 mg Chl a. M-2 for a pixel of 5 x 5 m. .
17
Dyson, Kirstie E. "Biodiversity and ecosystem processes in heterogeneous environments." Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/698.
Full textAbstract:
The decline in biodiversity over the last decade has motivated researchers to investigate the relationship between species richness (biodiversity) and ecosystem function. Empirical approaches are becoming more realistic as more factors have been included. Spatial heterogeneity is an example. Heterogeneity is an inherent part of the environment and apparent in all habitat types creating a patchy, mosaic of natural landscape. Researchers have reported the extent of heterogeneity in the landscape, but surprisingly not yet included heterogeneity into biodiversity and ecosystem function (BEF) studies. In recent years, empirical studies of marine systems have enhanced the BEF debate. Depauperate estuarine systems are ideal candidates for establishing model systems. In this study, estuarine microphytobenthos (MPB) were used as a response variable since the relationship between MPB and primary productivity is well-known. This relationship was exploited to employ MPB biomass as a proxy for primary productivity. Benthic chambers were used to assess the effect of macrofauna in single species and multi-species treatments on both ecosystem function and net macrofaunal movement. Heterogeneity was created through enriching sediment ‘patches’ with Enteromorpha intestinalis, providing areas of high and low nutrient. Heterogeneity, macrofaunal biomass, species richness, species diversity and flow were all varied in order to assess combined effects on the functioning of the system. Heterogeneity was found to have a significant influence on ecosystem functioning and on macrofaunal movement, however, patch arrangement did not. MPB biomass was highest in patches containing organic enrichment suggesting that nutrients were obtained locally from the sediment/water interface rather than the water column. There was variation in MPB biomass with macrofaunal species, probably resulting from differences in behavioural traits. It was also evident that flow altered species behaviour, as there was a significant difference between static and flow treatments. This work shows the importance of heterogeneity for BEF relationships.
18
Becker, Amani Eve. "Uptake and mobilisation of metals associated with estuarine intertidal sediment by microphytobenthic diatoms." Thesis, University of Stirling, 2017. http://hdl.handle.net/1893/25388.
Full textAbstract:
Microphytobenthos (MPB), a mixed community of microscopic, photosynthetic organisms, algae and cyanobacteria, inhabiting the top few millimetres of bottom sediment, is a key component of intertidal mudflats. It accounts for a significant proportion of estuarine primary production, forms the base of the food chain and influences sediment distribution and resuspension (through production of extracellular polymeric substances (EPS)). Diatoms dominate the microphytobenthos community in the mid-latitudes of the Northern Hemisphere. Estuarine sediments, are a sink for metal contaminants derived from fluvial, marine and atmospheric sources. Whilst metal releases to estuaries have declined in recent years due to increased regulation and declining industrial activity, metals previously discharged and which are now locked up in saltmarsh sediments remain a concern. For example, there are indications that saltmarshes are already being eroded, due to climate change related sea level rise, in some locations. This erosion may result in the redistribution of historically contaminated sediment to locations, such as the mudflats, where it is more available to biota, such as the MPB. In addition to causing redistribution, climate change effects, such as increasing temperatures and storminess, may also alter the bioavailability of metals to MPB. Increased concentrations of metals within the MPB could potentially increase their transfer to higher organisms through the food chain with potential impacts for biota. Whilst planktonic algae have been well studied with respect to metal uptake from the water column, there has been little research involving MPB and uptake of metals from sediment. The extent to which contaminant uptake by microphytobenthic algae occurs and under what conditions is therefore poorly understood. The research presented uses laboratory, mesocosm and field studies, to gain an understanding of processes governing metal bioavailability and mechanisms for uptake from sediment to the diatoms of the MPB under the complex and variable conditions of intertidal mudflats. A laboratory study using a single diatom species Cylindrotheca closterium found that uptake of cadmium (Cd) varied with sediment properties revealing the importance of sediment particle size and organic matter content in metal bioavailability to diatoms. Additionally, this study showed that the presence of diatoms altered Cd partitioning between sediment, overlying and pore water. Specifically there was an increase in Cd in the overlying and pore water when diatoms were present, indicating that diatoms mobilise metals from the sediment to the water column potentially increasing metal bioavailability to other biota. A study was conducted using an intertidal mesocosm to increase the realism of the study system and examine uptake to a natural MPB community. Diatoms were found to have higher concentrations of all the metals analysed (except tin) than other types of algae (filamentous and sheet macroalgae), confirming their importance as a study organism with respect to metal uptake and potential mobilisation through the food chain. Sediment disturbance was shown to increase metal uptake (iron, aluminium, vanadium and lead) from the sediment to algae. This is of concern due to predicted increases in storminess which are likely to increase sediment disturbance, with the likelihood that uptake of metals to diatoms will increase in the future. However, there were also indications of an antagonistic effect of temperature on disturbance, whilst disturbance increased bioavailability and uptake, increasing temperatures reduced uptake of some metals. This highlights the importance of considering the effects of multiple stressors in complex systems. Field studies showed that concentrations of some metals were related to their position on the mudflat whilst others were related to sampling date, indicating that there may be seasonal controls, such as to the presence of greater diatom biomass in spring and autumn, on metal uptake from the sediment. The research conducted has increased understanding of metal uptake to microphytobenthic diatoms from sediment and the influence they have in transferring metals from sediment to water, however the research also raises a number of new questions. For example, there appeared to be a link between sediment organic matter content and bioavailability of metals to diatoms, although the relative contribution of the diatoms, other algae, cyanobacteria and EPS to the sediment organic matter warrants further investigation. Furthermore, it has shown that the use of laboratory and mesocosm studies for this type of research can produce similar outcomes to those observed in the field but under more controlled and easily manipulated conditions, although field studies will continue to be vital in improving understanding of metals availability and transfer.
19
Liu, Yang. "L'influence de la méiofaune sur le fonctionnement du biofilm lotique en relation avec la qualité de l'eau." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30197/document.
Full textAbstract:
Le rôle de la méiofaune sur le fonctionnement des biofilms lotiques a été examiné par l'étude de son effet potentiel sur la capacité de consommation de l'azote des biofilms, au cours de quatre expérimentations. Les deux premières (Chapitres 2 et 3) concernent les biofilms épilithiques (phototrophes) tandis que les deux autres ont porté sur les biofilms (hétérotrophes) de la zone hyporhéique. Les biofilms sont soumis (1) à différents niveaux de densités (méiofaune) et à un enrichissement en nutriments ou (2) à différents niveaux de diversité (biofilm/méiofaune/macrofaune). Une partie des microcosmes présentant chaque niveau de diversité a été exposée à l'effet d'un herbicide, le diuron. Dans l'ensemble, la méiofaune associée aux biofilms des microcosmes était largement dominée par les rotifères. Les résultats basés sur les biofilms phototrophes montrent que les rotifères peuvent répondre à court terme, à un enrichissement en N-NO3 par une augmentation significative de leur densité et biomasse. De plus, le taux de consommation de N-NO3 est apparu significativement plus élevé dans les microcosmes dont les densités de méiofaune étaient les plus élevées. Cet effet positif de la méiofaune sur la consommation de N- NO3 par les biofilms a été retrouvé dans l'étude basée sur le biofilm hyporhéique pour les microcosmes non soumis aux effets du diuron. Dans l'ensemble, ce travail met donc en évidence le rôle significatif que peut avoir la méiofaune dans les processus de consommation de l'azote par les biofilms lotiques. De plus, les résultats suggèrent fortement que les invertébrés interagissent avec les micro-organismes impliqués dans les processus de réduction des concentrations en azote, dans le biofilm phototrophe comme dans le biofilm hyporhéique. Enfin, l'exposition à l'herbicide a engendré une modification significative du taux de consommation de N-NO3 dans les microcosmes hyporhéiques. Cependant, la comparaison du taux de consommation moyen de N-NO3 entre les traitements exposés à l'herbicide et ceux non exposés, a montré que la présence des invertébrés (méiofaune + macrobenthos) a significativement réduit l'effet du diuron sur ces processus. Cette étude met en exergue le rôle potentiellement important des interactions micro- organismes - invertébrés dans (1) le cycle de l'azote des biofilms et donc, dans les fonctions relatives à leur contribution aux processus " d'auto-épuration " des cours d'eau, et (2), dans la capacité de résistance des écosystèmes hyporhéiques face aux perturbations chimiquesThe role of meiofauna on the functioning of riverine biofilms was examined by studying their potential effect on nitrogen consumption capacity of biofilms in four experiments (Chapters 2 and 3: epilithic phototrophic biofilms; Chapters 4 and 5: heterotrophic biofilms of hyporheic zone). Biofilms are subjected to (1) different levels of densities (meiofauna) and nutrient enrichment or (2) different levels of diversity (biofilm/meiofauna/macrofauna). A part of the microcosms of each level of diversity was exposed to the effect of an herbicide, diuron. Overall, biofilm-associated meiofauna in microcosms was dominated by rotifers. Results in phototrophic biofilms showed that the response of rotifers to short-term nutrient enrichment was significant increases in their density and biomass. In addition, N-NO3 uptake rates appeared significantly higher in microcosms with highest meiofauna densities. This positive effect of meiofauna on biofilm N-NO3 uptake was also found in hyporheic biofilm microcosms, but not under the effect of diuron. Therefore, this thesis highlights that meiofauna can have a significant role in nitrogen consumption processes by lotic biofilms. In addition, the results strongly suggest that invertebrates interact with microorganisms involved in the reduction processes of nitrogen concentrations in the phototrophic biofilm as well as the hyporheic biofilm. Finally, the herbicide exposure resulted in a significant modification of N-NO3 uptake rate in hyporheic microcosms. However, the comparison of the average N- NO3 uptake rate between treatments exposed to herbicide and those unexposed, showed that the presence of invertebrates (meiofauna + macrofauna) significantly reduced the effect of diuron on these processes. This study highlights the potentially important role of microorganism-invertebrate interactions (1) in the nitrogen cycle of biofilms and thus functions related to their contribution to the "self-purification" process in streams, and (2) in resilient capacity of the hyporheic ecosystem to chemical perturbations
20
Johnson, Vivienne R. "A study of marine benthic algae along a natural carbon dioxide gradient." Thesis, University of Plymouth, 2012. http://hdl.handle.net/10026.1/1230.
Full textAbstract:
Increasing atmospheric CO2 is causing unprecedented changes in seawater chemistry, yet the uncertainty of the ecological response to these projected changes, termed ‘ocean acidification’, remains considerable at present. To predict the effects of these changes, we need to improve our understanding of the responses of marine primary producers since these drive biogeochemical cycles and determine the structure and function of benthic habitats. The majority of experiments on the effects of ocean acidification on photoautrophs to date have mainly focused on oceanic microalgae, leaving benthic assemblages largely overlooked. Carbon dioxide vents are providing a means for examining and predicting the impacts of ocean acidification on marine ecosystems. In this thesis a temperate CO2 volcanic vent gradient was used to investigate the responses of benthic microalgal assemblages (periphyton, epilithic, epipelic, epipsammic and endolithic) and macroalgae (a calcified phaeophyte, crustose coralline algae and turf algae) to increasing pCO2. The photosynthetic standing crop of microphytobenthic assemblages increased significantly with elevations in CO2 indicating that the productivity of shallow water habitats may be promoted over the course of this century. Some benthic diatoms appear to benefit in naturally CO2 enriched environments whilst benthic cyanobacteria in this study appear to be relatively insensitive to the levels of increase predicted for this century. Dramatic shifts in epilithic macroalgae assemblages were observed along the CO2 gradient and a calcified phaeophyte was revealed as an unexpected ecological winner under ocean acidification scenarios. These observations suggest that benthic algal assemblages have the potential to dramatically alter as CO2 levels continue to rise; this would have profound consequences for the structure and function of benthic ecosystems.
21
Neely, Merrie Beth. "Benthic Microalgae and Nutrient Flux in Florida Bay, USA." Scholar Commons, 2008. https://scholarcommons.usf.edu/etd/426.
Full textAbstract:
The objective of this study was to address the relationship between benthic microalgal communities and the phosphate nutrient dynamics of Florida Bay sediments and how they relate to benthic and water column primary production. In situ phosphate (P) flux between the sediment and the water column was measured in three regions of Florida Bay. Differences in the ratio of inorganic to organic phosphate flux were found between the three regions in relation to the amount of phosphate measured in the water column. Based upon the average sediment flux in my study, more than 1600 metric tons of P would be supplied by the sediment per year in Florida Bay.
Based upon my measurements, dissolved nutrient flux from the sediment can be an important contribution to pelagic phytoplankton blooms in Florida Bay, accounting for 6.5 - 41% of demand and TDN accounts for 100% of the N demand. My findings were similar to others for both benthic nutrient flux and benthic microalgal chlorophyll a concentration. Benthic microalgae in Florida Bay contribute 700 kg Chl a per day to the system.
Mesocosm experiments demonstrated that benthic microalgae and water column phytoplankton can respond differently to changes in nutrient availability. The dissolved nutrient in least supply in the water column does not necessarily correspond to the limiting nutrient for benthic microalgae.
³³P acted as a tracer between sediment and water column dissolved P pools. The presence of benthic microalgae enhanced the transport of ³³P to the water column as compared to simple Fickian diffusion. This was supported by the positive flux of dissolved P from the sediment to the water column pools in control treatments with a living benthic microalgal layer.
Primary production by benthic microalgae were measured using dissolved O2 evolution and PAM fluorometry. Primary production for BMA habitat in Florida Bay was between 400 and 800 tons of C per day, based upon O2 production and PAM fluorometry, respectively.
22
Savelli, Raphaël. "Study of microphytobenthos dynamics in temperate intertidal mudflats by using physical-biological coupled modelling and remote sensing data analysis." Thesis, La Rochelle, 2019. http://www.theses.fr/2019LAROS030.
Full textAbstract:
La production primaire (PP) élevée des vasières intertidales aux latitudes tempérées est principalement assurée par le microphytobenthos (MPB), qui soutient les réseaux trophiques benthiques et pélagiques. Dans cette thèse, nous utilisons un modèle couplé physique-biologie pour étudier la variabilité spatio-temporelle de la dynamique du MPB sur une vasière intertidale de la côte Atlantique française. Le modèle simule explicitement la biomasse du MPB et du brouteur Peringia ulvae. Les résultats fournissent des conclusions clés sur la dynamique du MPB. À l’hiver et au printemps, une lumière et une température de surface de la vase (TSV) optimales pour la croissance du MPB donnent lieu à une efflorescence printanière du MPB. La lumière est le facteur le plus limitant annuellement. Cependant, la TSV limite la croissance du MPB 40 % du temps en été. La photoinhibition pourrait se superposer à la thermoinhibition au printemps et en été. Le broutage et la remise en suspension (RES) du MPB façonnent également la dynamique du MPB. La bioturbation par P. ulvae contribue à une RES chronique du MPB du sédiment vers la colonne d’eau au printemps et en été. Les vagues contribuent à la RES du MPB par le biais d’événements de RES massive en hiver, au printemps et en automne. 50 % de la PP annuelle du MPB est exporté vers la colonne d’eau par le biais de RES chroniques et massives. Nous avons également développé une méthode qui combine les données de télédétection et les résultats du modèle couplé physique-biologique en un algorithme capable de prédire la PP à partir de données satellitales. En plus d’apporter de nouvelles perspectives sur la dynamique du MPB, ce travail propose de nouveaux outils numériques pour surveiller et prédire la PP du MPB et son devenir dans les eaux côtières dans un contexte de changement climatiqueThe high primary production (PP) of intertidal mudflats at temperate latitudes is mostly supported by microphytobenthos (MPB), which support both benthic and pelagic food webs. In the present thesis, we use a physical-biological coupled model to investigate the spatial and temporal variability of MPB dynamics on a large temperate intertidal mudflat of the French Atlantic coast. The model explicitly simulates the MPB biomass and the grazer (Peringia ulvae) biomass and density. The outputs provide key findings on MPB dynamics. In winter-spring, optimal light and mud surface temperature (MST) conditions for MPB growth lead to a MPB spring bloom. Light is the most limiting driver over the year. However, a high MST limits the MPB growth 40% of the time during summer. The photoinhibition of MPB photosynthesis can potentially superimpose on thermoinhibition in spring-summer. Grazing and resuspension of MPB biomass also shape the dynamics of the MPB biomass. Bioturbation by P. ulvae contributes to a chronic export of MPB biomass from the sediment to the water column in spring-summer. Waves contribute to the MPB resuspension through massive resuspension events in winter, spring and fall. 50% of the annual MPB PP is exported to the water column through chronic and massive resuspension events. We also developed a new method that combine remote sensing data with outputs of the physical-biological coupled model into a single algorithm that can predict PP from satellite data. In addition to bring new insights on the MPB dynamics, this work proposes new numerical tools to monitor and predict MPB PP and its fate in coastal waters in a context of climate change
23
Hanlon, A. R. M. "The effect of simazine on chlorophyll a fluorescence in axenic diatom monocultures and in estuarine microphytobenthic biofilms." Thesis, University of Essex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390991.
Full text
24
Chennu, Arjun [Verfasser], Ľuboš Akademischer Betreuer] Polerecký, Antje [Akademischer Betreuer] [Boetius, and Kai-Uwe [Akademischer Betreuer] Hinrichs. "Mapping the microscale variability of microphytobenthos: Development of a hyperspectral imaging method / Arjun Chennu. Gutachter: Antje Boetius ; Kai-Uwe Hinrichs. Betreuer: Lubos Polerecky." Bremen : Staats- und Universitätsbibliothek Bremen, 2014. http://d-nb.info/1072157284/34.
Full text
25
CARIOU-LE, GALL VALERIE. "Repartition spatio-temporelle du microphytobenthos dans un sediment vaseux intertidal du bassin de marennes-oleron et etude experimentale de sa remise en suspension." Paris 6, 1995. http://www.theses.fr/1995PA066279.
Full textAbstract:
L'importance et la repartition verticale du microphytobenthos sur une vasiere intertidale du bassin de marennes-oleron ont ete suivies au cours d'un cycle annuel par des analyses pigmentaires en c. L. H. P. Celles-ci ont revele la presence quasi exclusive de diatomees benthiques et le manque de materiel vegetal allochtone. Le biovolume des 6 especes principales explique a lui seul les variations saisonnieres des concentrations pigmentaires tandis que dans le plan vertical, les teneurs elevees mesurees jusqu'a 5 cm de profondeur ne correspondent pas a la presence de diatomees vivantes ; l'importance relative des differents pigments serait un indice de leur stabilite. Sur l'ensemble du suivi, les niveaux assez faibles de la biomasse algale suggerent une disparition importante des microphytes et l'abondance de certains pheopigments est un indice de l'intensite du broutage exerce par les invertebres benthiques ; l'accroissement de cette activite suit avec un leger decalage celui de la biomasse microalgale. Le microphytobenthos peut aussi alimenter les reseaux trophiques pelagiques par remise en suspension a maree haute. Ainsi, des experiences realisees en canal hydrodynamique sur des vases non consolidees soumises a la simulation d'un courant de maree ont montre que les sediments fluides sont facilement erodes. La cinetique du phenomene est influencee par la teneur en eau de la vase, d'une part, et par la bioturbation, d'autre part, les effets des facteurs physique et biologique pouvant etre combines. Le mollusque gasteropode h. Ulvae qui a servi de modele induit en particulier une remise en suspension precoce et amplifie le phenomene
26
Haubois, Anne-Gaëlle. "Dynamique des transferts trophiques entre le microphytobenthos et le gastéropode déposivore Hydrobia ulvae (Pennant) sur une vasière intertidale de la Baie de Marennes-Oléron." La Rochelle, 2003. http://www.theses.fr/2003LAROS108.
Full textAbstract:
Dans l'objectif d'analyser la dynamique du flux trophique entre le microphytobenthos et le gastéropode Hydrobia ulvae nous avons caractérisé la dynamique et la structure des compartiments étudiés, puis quantifié expérimentalement l'effet de ces facteurs, ainsi que celui des principales variables environnementales, sur le taux d'ingestion de H. Ulvae. La biomasse microphytobenthique oscille entre 40 et 150 mg Chl a m-2 à l'échelle saisonnière. La communauté microalgale se caractérise par la dominance de petites espèces. L'étude de la dynamique de population de H. Ulvae a montré l'influence de mouvements d'individus sur la structure locale de la population. Le taux d'ingestion de H. Ulvae varie principalement sous l'influence de la concentration en Chl a et de la taille des individus. La réponse des juvéniles et des adultes aux variations de Chl a se caractérise par une augmentation puissance du taux d'ingestion. L'ensemble de ces données a permis une estimation du flux trophiqueThe goal of my Ph. D. Was to characterize the spatio-temporal variation of the trophic transfer between microphytobenthos and the gastropod Hydrobia ulvae. I therefore investigated structure and dynamics of the two compartments and quantified experimentally the effect of demographic and environmental variables on the individual ingestion rate of H. Ulvae. Microphytobenthic biomass varied between 40 and 150 mg Chl a. M-2 and the diatom assemblage was dominated by small-sized species. The study of H. Ulvae population dynamics showed that the population structure is strongly influenced by large-scale movements of individuals. Individual ingestion rate of H. Ulvae is mainly controlled by the chlorophyll a concentration in the sediment and individual size. The functional response of H. Ulvae, juveniles and adults over a wide range of Chl a concentration is characterized by an increase of the ingestion rate according to a power law. Finally, all results were used to estimate the trophic flux
27
Guarini, Jean-Marc. "Modelisation de la dynamique du microphytobenthos des vasieres intertidales du bassin de marennes-oleron. Effets des synchroniseurs physiques sur la regulation de la production." Paris 6, 1998. http://www.theses.fr/1998PA066150.
Full textAbstract:
L'objectif de l'etude est de quantifier la dynamique spatio-temporelle de la biomasse microphytobenthique des vasieres intertidales de marennes-oleron. Un modele dynamique local a ete formule dans ce but ; il incorpore les processus de production, de migration active des microalgues epipeliques et de pertes de biomasse par mortalites et par remise en suspension dans la colonne d'eau. La spatialisation est conditionnee par un modele hydrodynamique qui calcule la hauteur d'eau en tout point. L'environnement photique du microphytobenthos est decrit de facon discrete par une couche s de diatomees en surface du sediment et une couche f representant le centimetre superficiel de la vase. La migration verticale active des cellules definit les echanges entre ces deux couches, orientes du fond vers la surface en periode d'exondation diurne et de la surface vers le fond en periodes d'exondation nocturne et de submersion. A cause de cette difference de comportement migratoire, deux sous-systemes d'equations differentielles ont ete formules. Pendant la periode d'exondation diurne, seules les algues en surface peuvent photosynthetiser, en beneficiant de la totalite de la lumiere incidente ; le nombre de places en surface est limite si bien que les echanges du fond vers la surface sont densite-dependants. Les processus de production ont ete etudies experimentalement ; en particulier, le controle a court-terme de la capacite photosynthetique par la temperature a ete mis en equation. Par la suite, un modele decrivant la dynamique de la temperature de surface de la vase a permis de caracteriser le forcage des potentialites de production a l'echelle de l'ecosysteme et a mis en evidence un phenomene de thermo-inhibition qui se generalise en ete. Les processus decrivant les pertes de biomasses sont consideres comme globaux et sont des fonctions lineaires de la biomasse microphytobenthique. Il a ete montre qu'un tel systeme, commutant rapidement entre les deux etats (exondation diurne et exondation nocturne+submersion), atteignait un equilibre cyclique, valide localement par des observations. Le modele peut en outre expliquer la dynamique saisonniere, particulierement la baisse locale de biomasse en ete. Cependant, les processus qui decrivent les pertes de biomasse ne sont pas assez bien definis pour permettre de representer correctement les structures spatiales observees. Des perspectives sont proposees pour y remedier, qui necessitent de nouvelles experimentations ; le modele existant peut alors servir de base pour tester les hypotheses du fonctionnement du systeme.
28
Redzuan, Nurul Shahida. "Microphytobenthos (MPB) biomass variability and sediment-water column exchanges on an intertidal flat : influence of weather-related abiotic factors across neap-spring-neap tidal cycles." Thesis, University of Essex, 2017. http://repository.essex.ac.uk/19959/.
Full textAbstract:
The spatio-temporal distribution of microphytobenthos (MPB) on the sediment surfaces during emersions and suspended in water column during immersions was investigated on transects across Fingringhoe Tidal Flat in Colne estuary, on three zones: the mud flat, the transition zone and the salt marsh. The results of this thesis suggest that MPB distribution on intertidal flat was controlled by a set of complex interaction between the MPB with both biotic and abiotic factors. How much MPB are there on the sediment surfaces determines the availability of MPB biomass after immersion period and in the water column during immersion. ‘Sum of sun hours’ and ‘sum of rainfall’ directly affected the MPB biomass on sediment surfaces, and consequently, indirectly affected the MPB that associated with suspended sediment in the water column during immersions. Tidal range did not have significant effect on MPB biomass on sediment surfaces, however was significantly negatively effected the suspended MPB on the mud flat and the transition zone. The Chl a on the salt marsh however was significantly positively correlated with the tidal range. Data of net settlement rate of suspended sediment per hour during immersions displayed positive relationship with MPB biomass availability after immersion. The sediment settlement on the intertidal flat was negatively correlated with mean wind speed and tidal range. Neap-spring-neap tidal cycles were found to nfluence MPB species composition across the tidal flat. Spring tide that was characterized by high water current and high tidal range (4.3 – 5.6 m) showed to increase the occurrence of centric diatom such as species from genus Coscinodiscus, genus Actinoptychus and Odontella on both mud flat and transition zone. Also, the spring tide was responsible to source the salt marsh with species that commonly recorded on the mud flat and transition zone such as Pleurosigma angulatum and species from genus Gyrosigma.
29
Sevilgen, Duygu Sevgi [Verfasser], Thomas [Akademischer Betreuer] Brey, and Kai [Akademischer Betreuer] Bischof. "Microphytobenthos in cold-water sublitoral systems : their ecological role and response to changing environmental conditions / Duygu Sevgi Sevilgen. Gutachter: Thomas Brey ; Kai Bischof. Betreuer: Thomas Brey." Bremen : Staats- und Universitätsbibliothek Bremen, 2014. http://d-nb.info/1072225670/34.
Full text
30
Duggan, Melissa. "Effect of River Flow on Downstream Productivity in a Tropical Estuary." Thesis, Griffith University, 2012. http://hdl.handle.net/10072/366499.
Full textAbstract:
This thesis provides significant insight into the effect of seasonal patterns of flooding on estuarine function in the wet-dry tropics by exploring the impact of seasonal freshwater flow on benthic biota in the wet-dry tropical Norman River estuary of northern Australia. This thesis also describes the construction of a model designed to predict the potential impact of freshwater flow regulation on key estuarine biota. Flow regimes in the wet-dry tropics are characterised by seasonal patterns of summer wet season floods and low or no freshwater flow for the rest of the year. Few studies exist on wet-dry tropical estuaries, and none have sampled the estuary before, during and after wet season floods of different magnitude. Research within this thesis has increased the understanding of estuarine function in the wet-dry tropics, and the short and long term impacts of the magnitude of wet season flooding on benthic biota (meiofauna and microphytobenthos) was identified. These findings were combined with information on commercially important banana prawns (Penaeus merguiensis) in the Norman River estuary to construct a Bayesian Network (BN) model. The model explored the drivers of change in the Norman River estuary under currently natural patterns of flow, and the likely impact of future water resource development on banana prawns and their key food source, meiofauna and MPB (microphytobenthos).Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text
31
Barnett, Alexandre. "Régulation de l'activité photosynthétique du microphytobenthos et conséquence sur la dynamique temporelle de la production primaire dans les vasières intertidales de la côte atlantique de l'Europe de l'Ouest." Thesis, La Rochelle, 2013. http://www.theses.fr/2013LAROS412/document.
Full textAbstract:
Le microphytobenthos (MPB) des latitudes tempérées est dominé par les diatomées. Deux grands groupes se distinguent, les épipéliques (mobiles) des sédiments vaseux, et les épipsammiques (fixées) des sédiments sablo-vaseux. Afin de mieux comprendre la production des vasières, le MPB a été étudié par des approches du niveau physiologique au niveau écologique. Dans un premier temps, l’étude s’est focalisée sur des expérimentations en laboratoire. La réponse des différents groupes à la lumière a montré que la forme de vie et la mobilité sont en lien étroit avec la capacité de photoprotection physiologique. Ainsi, les diatomées non-mobiles présentent une meilleure photoprotection physiologique que les diatomées mobiles qui peuvent fuir les excès de lumière. Dans une deuxième partie, le travail s’est effectué sur des échantillons ramenés en laboratoire. Des profils de migrations ont été réalisés par mesure continue de la fluorescence. Il a été établi que le MPB présente un rythme de migration interne pouvant être modulé par la lumière. De plus la qualité de la lumière modifie les profils de migration. Il est communément admis que les phases de division cellulaire se dérouleraient en profondeur. La cytométrie en flux permet de vérifier cette hypothèse. Finalement les mesures effectuées en laboratoire ont été comparées à des mesures effectuées directement sur le terrain à l’échelle de la communauté. Il a ainsi pu être vérifié que la photoprotection sous lumière fluctuante est fonction de la population. Pour les populations épipéliques, la photoprotection physiologique ne varie pas au cours des fluctuations lumineuses, laissant supposer que la migration module ces fluctuations. Les populations épipsammiques, quant à elles, modifient leur réponse physiologique en fonction des fluctuations lumineusesMicrophytobentos (MPB) from temperate latitude is mainly composed of diatoms. Those microorganisms can be separated in two groups: the epipelic one from muddy sediments (composed of mobile diatoms) and the epipsammic one from sandy-muddy sediments (composed of diatoms living attached to their substrate). In order to investigate mudflats’ primary production, the MPB compartment was studied through diverse approaches from the physiological level to the ecological one. In the first place, laboratory experiments (in vitro experiments), focusing on light reaction of epipelic and epipsammic diatoms, showed that their life form and their mobility were strongly connected to their physiological photoprotection ability. Thereby, the motionless diatoms were characterized by higher physiological photoprotection abilities than the mobile ones, which could avoid excess of light. In the second place, the fluorescence of collected samples (in vivo experiments) was measured to acquire diatoms’ migration profiles. The results pointed out an internal and light-regulated migration pattern of the MPB and furthermore highlighted the effect of light quality on migration profiles. Besides, the commonly accepted hypothesis of deep cell division phases was tested and confirmed through flow cytometry experiments. Eventually, laboratory measurements were compared to in situ ones realized at the scale of the whole community. These comparisons revealed that diatoms photoprotection in fluctuating light depended on the targeted populations. Epipelic organisms were indeed characterized by an unvarying photoprotection, diatoms migration regulating alone the effect of light fluctuations. On the contrary, motionless epipsammic populations required a light-regulated photoprotection
32
Nzigou, Aimé Roger. "Production primaire et fonctionnement écologique en milieu estuarien turbide : cas de l’estuaire de la Gironde (France)." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14674/document.
Full textAbstract:
La compréhension des processus écologiques affectant la matière transitant ou produite dans les estuaires nécessite une bonne connaissance des facteurs qui contrôlent le développement des différents groupes biologiques et leurs relations trophiques dans le milieu.Les milieux estuariens macrotidaux sont le plus souvent caractérisés par des fortes turbidités qui limitent généralement la production primaire locale. Ils présentent cependant une forte productionsecondaire et des concentrations en chlorophylle non négligeables dans la colonne d’eau. L’une des problématiques demeure donc l’origine de cette production primaire dans les eaux turbides de ces milieux. Cette thèse s’inscrit dans cette logique ; dans la continuité des travaux réalisés précédemment. Elle vise à analyser l’importance et le rôle de la production primaire dans la production globale de l’estuaire de la Gironde. Le présent manuscrit résume ainsi l’ensemble des travaux réalisés et lesrésultats obtenus sur les principaux groupes de producteurs primaires (phytoplancton et microphyto-benthos) présents le long du continuum fluvio-estuarien de la Gironde. Les principales questions qui sont développées dans ce travail structurent ce rapport en trois axes de recherche. Le premier axe permet, au moyen d’une modélisation 1D de transport et réaction, de simuler,dans l’espace et le temps, la dynamique de la chlorophylle-a et des sels nutritifs, témoins d’uneproduction primaire dans le milieu. Les résultats indiquent que la dynamique de la chlorophylle-adans la Gironde reste fortement dépendante des débits et des temps de résidence très courts des massesd’eau, renforçant ainsi une origine allochtone du phytoplancton. Parmi les sources potentielles deproduction d’origine allochtone présents dans la colonne d’eau, les microalgues benthiques jouent unrôle majeur puisqu’elles peuvent être remises en suspension au cours de chaque marée. L’analyse dece compartiment et de sa production a permis dans un second axe de travail, de montrer que les zonesintertidales situées en aval de l’estuaire sont les plus productives et sont majoritairement autotrophes.Elles produiraient relativement plus de matière que les zones situées en amont qui elle, sont fortementinfluencées par les débits des fleuves.Finalement dans le troisième axe, les différentes voies de transfert de la matière organique au seindu réseau trophique, où les copépodes occupent une place prépondérante, sont analysées au moyendu traçage par les isotopes stables de carbone et de l’azote (13C et 15N)Abstract
33
Pniewski, Filip Franciszek. "Capacité photosynthétique du microphytobenthos des vasières intertidales de la Baie de l'Aiguillon (Côte atlantique, France) et des lagunes non-tidales de faible profondeur de la Baie de Puck (Mer Baltique, Pologne)." Thesis, La Rochelle, 2010. http://www.theses.fr/2010LAROS300.
Full textAbstract:
Dans les écosystèmes littoraux, les communautés microphytobenthiques sont soumises à des conditions environnementales qui peuvent être extrêmes en particulier en ce qui concerne l'intensité lumineuse. Les mécanismes de protection mis en place dépendent étroitement du type d'habitat où se développent ces communautés et cette thèse a pour objectifs d'analyser les caractéristiques de l'activité photosynthétique et les mécanismes de protection développés par des assemblages microphytobenthiques dans deux écosystèmes littoraux très différents : les vasières intertidales atlantiques de la Baie de L'Aiguillon (France) et la lagune côtière non tidale de Puck Bay dans la Mer Baltique (Władysławowo, Pologne). Pour réaliser ces objectifs, trois études ont été réalisées : (1) la description des communautés microphytobenthiques, (2) la caractérisation de leur activité photosynthétique et (3) l'analyse des mécanismes de photoinhibition et de photoprotection.La structure taxonomique du microphytobenthos a été décrite en se basant sur des observations en microscopie optique et sur la mesure des caractéristiques des pigments photosynthétiques par chromatographie liquide à haute performance (HPLC). L'activité photosynthétique a été étudiée par des méthodes de microrespirométrie volumétrique et de spectrofluorométrie de la chlorophylle a. Les mécanismes de photoinhibition et de photoprotection ont été étudiés par fluorométrie en modulation d'amplitude pulsée (PAM).Les résultats obtenus nous ont permis de montrer que :1) Les communautés atlantiques sont fortement dominées par des diatomées épipéliques, alors que le microphytobenthos de la Mer Baltique est plus diversifié et comporte, outre des diatomées, une large part de cyanobactéries,2) Les microphytobenthos atlantique est bien acclimaté à des valeurs d'intensités lumineuses plutôt faibles, alors que les communautés de la Mer Baltique ont encore une bonne activité photosynthétique à de fortes irradiances,3) Les diatomées atlantiques présentent une plus forte photoinhibition que les microalgues de la Baltique,4) L'activité photosynthétique des communautés microphytobenthiques non perturbées montre un des rythmes circadien et tidal, qui semblent être contrôlés par des facteurs endogènes, qui mettent en jeu des adaptations comportementales comme la migration verticale pour les diatomées atlantiques,5) En ce qui concerne le microphytobenthos de la Mer Baltique, qui n'a pas de capacité migratoire, la photoprotection est assurée en premier lieu par la mise en jeu de processus physiologiques. Nous avons pu montrer la très grande flexibilité du photsystème PSII qui est capable de suivre très rapidement les changements à court terme de lumière ambianteThe scope of this thesis includes the characteristics and comparison of photosynthetic activity and photoprotection mechanisms of microphytobenthos assemblages inhabiting the Atlantic intertidal mudflats of Aiguillon Bay (Esnandes, France) and the littoral zone of the Baltic Sea in non-tidal Puck Bay (Władysławowo, Poland). In order to accomplish the main aims of the work the following tasks were carried out: (1) characterization of microphytobenthic assemblages; (2) characterization of their photosynthetic activity and (3) description of photoinhibition and photoprotective mechanisms. The structure of microphytobenthos was described based on observation of the material in light microscope (LM) and through the characteristics of photosynthetic pigments using high performance liquid chromatography (HPLC). Photosynthetic activity was described using various methods including classical (volumetric micro-respirometer) and modern (chlorophyll a fluorescence) ones. In addition, the measurements of variable fluorescence were also used to study photoinhibition and photoprotective mechanisms. Based on the obtained results it was stated that:1.) the Atlantic assemblages were strongly dominated by epipelic diatoms, while the Baltic microphytobenthos was more diverse and cyanobacteria, next to diatoms, were also very important component,2.) it was shown that the Atlantic microphytobenthos was well acclimated to rather low light intensities, while the Baltic assemblages showed good utilization of higher irradiance,3.) the Atlantic diatoms were more susceptible to photoinhibition than the Baltic microalgae,4.) the photosynthetic activity described for the undisturbed microphytobenthos communities revealed circadian and circatidal rhythms, which seemed to be controlled by endogenous factors, supporting diatoms’ behavioural adaptations i.e., vertical migration,5.) in case of the Baltic microphytobenthos, the lack of the ability to move caused their physiological processes the first line of defence against excess irradiances. The analysis revealed extreme flexibility of PSII which was able to follow rapidly the short-term changes in ambient light
34
Bertolli, Lucielle Merlym. "Estudo da comunidade de diatomáceas (BACILLARIOPHYTA) epifíticas em marismas da costa do sul do Brasil." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/158308.
Full textAbstract:
Diatomáceas são importantes constituintes do epifíton em ambientes costeiros. Estratégias de fixação conferem a estas algas vantagem adaptativa, no entanto, as mesmas estão sujeitas às variações ambientais, podendo responder com alterações da composição e estrutura da comunidade. Embora a relação entre epifíton e substrato seja pouco compreendida, a arquitetura do substrato parece influenciar na comunidade aderida. A composição, estrutura e variação sazonal de diatomáceas epifíticas foram avaliadas em ambientes de marismas no estuário da Lagoa dos Patos, sul do Brasil. Três sítios foram amostrados, Saco do Silveira, Ilha da Pólvora e São José do Norte, distantes 36, 18 e 9 km do oceano Atlântico, respectivamente. O epifíton aderido à Spartina alterniflora Loisel., Spartina densiflora densiflora Brogn., Scirpus maritimus L. e Juncus kraussii Hochst. foi removido dos substratos com lâmina metálica, oxidado e montado em lâminas permanentes para a análise das diatomáceas. Ao total cento e vinte e sete táxons foram encontrados, destacaram-se pelo maior número de espécies os gêneros Navicula Bory, Nitzschia Hassall e Tryblionella W. Smith. A sazonalidade, espacialidade, salinidade e tipo de substrato tiveram influência na composição e estrutura da comunidade. A maior distância da desembocadura do estuário proporcionou uma maior influência de águas continentais no sítio Saco do Silveira, resultando na formação de uma comunidade caracterizada pela presença de táxons dulciaquícolas. O período de inverno se caracterizou por maiores valores dos atributos da comunidade (riqueza, diversidade e equitabilidade). A maior complexidade da superfície de Scirpus maritimus proporcionou a formação de uma comunidade epifítica mais rica. A investigação taxonômica de Nitzschia e Tryblionella foi aprofundada, analisando-se também o microfitobentos da região. A espécie Nitzschia papillosa Bertolli et al. foi registrada pela primeira vez para a ciência, ocorrendo no epifíton e microfitobentos dos sítios Ilha da Pólvora e São José do Norte. A espécie possui formato linear-lanceolado, ápices cuneados e fíbulas irregularmente distribuídas como várias espécies do gênero, sua característica diagnóstica é a presença de excrecências de sílica arredondadas a quadradas situadas na costa transapical interna das valvas. O estudo do gênero Tryblionella revelou a presença de 11 espécies, duas foram registradas pela primeira vez para o Rio Grande do Sul e uma para o sul do Brasil. Além disso, duas espécies novas para a ciência são propostas, Tryblionella Bertolli et Torgan, espécie semelhante a T. debilis Arnott ex O’Meara em microscopia óptica, mas que apresenta costelas transapicais assimétricas em microscopia eletrônica, e Bertolli et al., espécie que apresenta um padrão de ornamentação na face valvar semelhante à trama de uma renda. As espécies de Tryblionella e N. papillosa ocorreram concomitantemente no epifíton e no microfitobentos, evidenciando a interação entre as duas comunidades, promovida pela dinâmica do ambiente.Diatoms are an important component of the epiphyton in coastal environments. The strategies of attachment provide adaptive advantages to these algae; however, they are susceptible to the environmental fluctuations, responding to them with changes in the community composition and structure. Although the relationship between epiphyton and substrate is poorly understood, the architecture of the substrate seems to influence the attached community. The composition, structure and seasonal variations of the epiphytic diatoms were evaluated in Patos Lagoon salt marshes. Three sampling sites were defined, Saco do Silveira, Ilha da Pólvora and São José do Norte, distant 36, 18 and 9 km from the Atlantic Ocean, respectively. The epiphyton attached to Spartina alterniflora Loisel., Spartina densiflora densiflora Brogn., Scirpus maritimus L. e Juncus kraussii Hochst. was scraped with metal blade, oxidized and mounted on permanent slides for the analysis of the diatoms. A total of a hundred and twenty seven taxa were found. The genus Navicula Bory, Nitzschia Hassall e Tryblionella W. Smith showed the highest number of species. The seasonality, spatiality, salinity and substrate influenced the composition and structures of the community. The higher distance of the estuary mouth provided a higher influence of continental waters in the site Saco do Silveira, resulting in a community characterized by freshwater taxa. The winter was characterized by higher values of the community attributes (richness, diversity and evenness). The more complex structure of S. maritimus surface provided the establishment of a richer community. The taxonomic investigation of Nitzschia and Tryblionella was more detailed, including the analysis of the microphytobenthos of the sites. The species Nitzschia papillosa Bertolli et al. was registered for the first time to science in Ilha da Pólvora and São José do Norte. The species has linear-lanceolate outline, cuneate apices and fibulae irregularly distributed, as many other species of the genus. Its main feature is the presence of rounded to squarer silica excrescences, situated on the transapical costae in the internal valve view. The study of the genus Tryblionella showed 11 species, two of them were registered for the first time in Rio Grande do Sul State and one in Southern Brazil. Besides that, two species new to science were proposed, Tryblionella Bertolli et Torgan, which is similar to T. debilis Arnott ex O’Meara in light microscopy, but present asymmetrical transapical ribs in scanning electron microscopy, and T. Bertolli et al. which presents an ornamentation pattern similar to a lace texture in the valve face. The species of Tryblionella and N. papillosa occurred concomitantly in the epiphyton and microphytobenthos, evidencing the interaction between both communities, promoted by the environment dynamics.
35
Santos, Paulo J. P. dos. "Contribution à l'écologie du méiobenthos et du microphytobenthos dans la zone oligo-mesohaline de l'estuaire de la Gironde et dynamique de population et production secondaire du copepode harpacticoi͏̈de Nannopus palustris Brady, 1880." Bordeaux 1, 1995. http://www.theses.fr/1995BOR11409.
Full textAbstract:
Le microphytobenthos et la meiofaune ont été étudies dans la zone oligo-mejohaline de l'estuaire de la gironde. La distribution spatiale et la dynamique de la biomasse du microphytobenthos ont été analysées, et une estimation de la production primaire est presentée. La variabilite saisonnière de l'abondance et de la composition de la meiofaune ont été decrites et mises en relation avec les facteurs environnementaux. L'influence de la distribution en agregats du microphytobenthos sur la répartition du meiobenthos a été étudiée. La production secondaire et dynamique de la population du copepode nannopus palustris a été le sujet d'une étude spécifique.
36
Santos, Paulo J. P. dos. "Contribution à l'écologie du méiobenthos et du microphytobenthos dans la zone oligo-mesohaline de l'estuaire de la Gironde et dynamique de population et production secondaire du copepode harpacticoi͏̈de Nannopus palustris Brady, 1880." Bordeaux 1, 1995. http://www.theses.fr/1995BOR10687.
Full textAbstract:
Le microphytobenthos et la meiofaune ont été étudies dans la zone oligo-mejohaline de l'estuaire de la gironde. La distribution spatiale et la dynamique de la biomasse du microphytobenthos ont été analysées, et une estimation de la production primaire est presentée. La variabilite saisonnière de l'abondance et de la composition de la meiofaune ont été decrites et mises en relation avec les facteurs environnementaux. L'influence de la distribution en agregats du microphytobenthos sur la répartition du meiobenthos a été étudiée. La production secondaire et dynamique de la population du copepode nannopus palustris a été le sujet d'une étude spécifique.
37
Vanhuysse, Charles. "Impacts de l'ostréiculture à mésoéchelle sur le microphytobenthos et ses performances photosynthétiques, la macrofaune benthique et rôle de l'érosion estuarienne dans les mortalités de naissains d'huitres Crassostrea gigas liées à OsHV-1 μ Var Drivers of epipelic mictophytobenthic photobiology and groth in oyster farm Benthic macrofaunal changes in oyster parks during an OsHV-1 µVar oyster spat mortality outbreak Environmental dynamics of the Ostreid herpes virus (OsHV-1 µVar) in oyster spats and microphytobenthic biofilms during an in situ mortality outbreak In situ resuspension of benthic sediments and biofilm components during an OsHV-1 µVar Crassostrea gigas oyster spat mortality episode." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC262.
Full textAbstract:
Depuis 2008, la mortalité des naissains d'huîtres Pacifique Crassostrea gigas est principalement liée au virus de l’ostreid herpesvirus 1 µvariant (OsHV-1 µVar). Les paramètres environnementaux favorisant la persistance et la diffusion du virus pourraient jouer sur sa dynamique de propagation. Les objectifs de cette thèse étaient d’étudier in situ les interactions entre les naissains d’huîtres et leur environnement benthique lors d’un épisode de surmortalité. La photobiologie du microphytobenthos sous les tables semblait en meilleur état comparé à celle observée dans les allées pouvant favoriser la résilience virale. Les tables à huîtres atténuaient la lumière, la température et la dessication évitant ainsi une thermo et photoinhibition du microphytobenthos. Les indices de la qualité environnementale de l’habitat benthique basés sur la communauté macrozoobenthique ont traduit une dégradation du milieu suite aux apports de matière organique induits par les mortalités de naissains d’huîtres puis des échouages des macroalgues. Une quantité importante d’OsHV-1 était retrouvée à la surface du biofilm avant les mortalités. Sa remise en suspension était préférentiellement associée aux particules microphytobenthiques avec de faibles courantsSince 2008, the mortality of Pacific oyster spat Crassostrea gigas has mainly been linked to the Ostreid herpesvirus 1 μvariant (OsHV-1 μVar). Environmental parameters favoring the persistence and spread of the virus could affect its propagation dynamics. The objectives of this thesis were to study in situ the interactions between oyster spat and their benthic environment during an episode of mortality. The photobiology of the microphytobenthos beneath the tables seemed to be in a better state compared to that observed in aisles that could promote viral resilience. The oyster tables attenuated light, temperature and desiccation, thus avoiding thermo and photoinhibition of the microphytobenthos. The benthic habitat environmental quality indices based on the macrozoobenthic community showed a degradation of the environment following the influx of organic matter induced by oyster spat mortalities and strandings of the macroalgae. A significant amount of OsHV-1 was found on the surface of the biofilm before the mortalities. Resuspension was preferentially associated with microphytobenthic particles with small currents
38
Heijden, Luuk van der. "Determination of the food sources and of the role of meiofauna in soft-bottom intertidal habitats of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany : importance of the microphytobenthos-meiofauna pathway, highlighted by community structure, trophic markers and linear inverse food web models." Thesis, La Rochelle, 2018. http://www.theses.fr/2018LAROS030/document.
Full textAbstract:
La méiofaune joue un rôle important dans le fonctionnement des habitats benthiques à substrat meuble (ex. flux de matière) en relation avec sa production élevée, sa position trophique intermédiaire et les importants transferts d’énergie vers les niveaux trophiques supérieurs qui y sont lié. Les relations trophiques et les flux de matière organique liés à la méiofaune restent néanmoins mal connus ou peu pris en compte. Afin de mieux appréhender le rôle de la méiofaune, la structure des communautés et les relations trophiques entre les sources de nourriture et ces consommateurs ont été déterminées dans cinq habitats à substrat meuble (i.e., vasière nue, herbier, zone à sables) de la baie de Marennes-Oléron, France, et de la baie de Sylt-Rømø, Allemagne, en tenant compte des variations temporelles. Le peuplement de méiofaune s’est trouvé être dominé par les nématodes et les copépodes benthiques. Les biomasses de microphytobenthos et de matière organique du sédiment sont apparues comme étant deux facteurs structurants pour les communautés. L’utilisation combinée de différents traceurs de la matière (i.e., isotopes stables, acides gras) a démontré que le microphytobenthos et les bactéries étaient les ressources trophiques majeures de la méiofaune dans les cinq habitats étudiés. Les mesures réalisées sur la structure des communautés et les données issues des traceurs de la matière ont été implémentées dans des modèles de réseaux trophiques. Dans tous les habitats, ces modèles ont mis en évidence que le flux de carbone dominant était issu du microphytobenthos, ceci démontrant les très faibles changements de comportements alimentaires malgré les importantes différences de sources trophiques en termes de disponibilité et de production des sources de nourriture entre ces différents habitats. Tous les groupes trophiques de nématodes, à l’exception des déposivores sélectifs, étaient particulièrement sélectifs et s’alimentaient majoritairement à partir de microphytobenthos, ceci étant à l’origine d’une forte production et d’un court temps de renouvellement de la méiofaune. En conclusion, cette thèse démontre le rôle important de la méiofaune dans les habitats à substrat meuble ainsi que l’importance de la relation trophique entre le microphytobenthos et la méiofaune dans le fonctionnement de ces réseaux trophiquesMeiofauna play an important role in ecosystem processes in soft-bottom benthic habitats, e.g. food web dynamics, related to their highproduction, their intermediate trophic position and the energy they transfer towards higher trophic levels. The trophic linkages and flows of organic matter related to the meiofauna remain poorly known or taken into account. To better assess the role of meiofauna, the community structure and trophic relationships between food sources and meiofauna were determined in five intertidal soft-bottom habitats (i.e., mudflat, seagrass bed, sandflat) of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany, taking temporal variations into account. Meiofauna communities were dominated by nematodes and benthic copepods. Biomass of microphytobenthos and of sediment organic matter were two of the major drivers of community structure. The combination of trophic markers (i.e., stable isotopes, fatty acids) demonstrated that microphytobenthos and bacteria were the major food sources of meiofauna in the five habitats. Information from community structure assessments and trophic marker analyses were implemented in food web models. In all habitats, these models demonstrated that the main flow of carbon to meiofauna originated from microphytobenthos, highlighting negligible changes in meiofauna feeding behavior besides the large differences in availability and productivity of food sources between these habitats. All trophic groups of nematodes, except for selective deposit feeding nematodes, were highly selective and mainly fed on microphytobenthos, resulting in a high production and a short turn-over time of meiofauna. In conclusion, this thesis demonstrated the important role of meiofauna in soft-bottom habitats as well as the importance of the trophic pathway from microphytobenthos to meiofauna in the functioning of these food webs
39
Oakes, Joanne. "Microalgae and Mangroves as Carbon Sources for Estuarine Invertebrates: Evidence from Stable Isotope Enrichment Experiments." Thesis, Griffith University, 2007. http://hdl.handle.net/10072/365499.
Full textAbstract:
The importance of different sources of carbon (energy) supporting secondary productivity in estuaries and coastal waters is still rather uncertain, despite decades of research on this topic. One of the major uncertainties is the relative importance of carbon from macrophyte detritus and microalgae, particularly diatoms and cyanobacteria within sediments (microphytobenthos, MPB). Existing methods have been unable to determine their relative contributions to consumer nutrition. This thesis addresses some of the limitations of existing methods, and then uses an innovative combination of techniques to determine the relative contributions of detritus and MPB to the nutrition of consumers within a mangrove forest in southeast Queensland, Australia. To ensure wide applicability, techniques were developed for both mud and sand, encompassing the range of sediments encountered in estuaries and protected coastal waters. Stable isotope analysis is commonly used to resolve food web issues. Difficulty extracting MPB from sediment to obtain a pure carbon isotopic signature (δ13C), however, has hampered efforts to determine the importance of MPB as a carbon source for consumers. I showed that compound-specific isotope analysis of phytol, part of the chlorophyll molecule, can be used to estimate MPB δ13C with enough precision for most food web studies: within 1-1.8‰ of actual values (95% CI) at normal levels of replication (n = 5 or 10). Although the majority of phytol in sediments is produced in situ by MPB, part of the phytol pool is derived from detritus (e.g. 33% for mud, 17% for sand in the current study). In some situations, this could lead to errors in estimating MPBδ13C, realistically by about 1‰ (in sand) or 2‰ (in mud), but an adjustment can be made where necessary. Compound-specific isotope analysis of phytol (the phytol method) can therefore be confidently used to estimate MPB δ13C values in estuarine environments. Where δ13C values of detritus and MPB are similar, natural abundance stable isotopes are unable to resolve their contribution to consumer nutrition. Enrichment of producers with the heavy 13C isotope generates distinct δ13C values that can be traced into consumers. Studies aiming to enrich MPB using 13C-enriched sodium bicarbonate have, however, observed simultaneous enrichment of bacteria. This may simply be due to use of MPB-derived carbon by bacteria, but if bacteria acquire the label directly, enrichment of consumers would indicate use of bacteria, rather than MPB, as a primary carbon source. Application of 13C-enriched bicarbonate resulted in enrichment of MPB in both mud and sand and subsequent secondary enrichment of bacteria. Direct bacterial uptake was trivial in comparison to MPB uptake. Any labelling of animals in subsequent enrichment experiments could therefore be attributed to use of MPB as a primary carbon source. I used a combination of the phytol method, stable isotope enrichment, and compartment modelling within a mangrove forest to examine use of detritus and MPB as carbon sources for common consumers; crabs (Australoplax tridentata and Parasesarma erythrodactyla) and foraminifera (Ammonia beccarii and Trochammina inflata). Compartment modelling quantified the extent of use through comparison of producer and consumer enrichment over time. The main carbon source for T. inflata was unable to be established, but all other species acquired virtually all of their carbon locally (within a 1 m radius), from MPB and/or mangrove detritus. The majority of carbon for A. tridentata was derived from MPB (99%), whereas P. erythrodactyla and A. beccarii predominantly utilised mangrove detritus (88 and 84%, respectively). For the latter two species, the remainder of carbon was derived from MPB. The different strategies in carbon utilisation by the crab species indicate feeding selectivity that may be a strategy to avoid interspecific competition for food resources. The high abundance of benthic invertebrates and their rapid assimilation of local carbon sources highlight their potential importance in influencing carbon cycling and productivity in estuaries. Consumption of benthic invertebrates by more mobile, higher consumers may also allow for transport of locally-produced carbon to adjacent waters via trophic relay. The methods demonstrated in this thesis have potential application in resolving food web issues in a variety of habitats. Further application of these techniques at a variety of temporal and spatial scales would help to develop a broader understanding of the importance of macrophyte detritus and MPB, and establish general patterns in utilisation of carbon sources in estuarine systems.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment
Faculty of Environmental Sciences
Full Text
40
Andersson, Eva. "Benthic-Pelagic Microbial Interactions and Carbon Cycling in Clearwater Lakes." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5798.
Full text
41
Almeida, Cristiano de Salles. "Distribuição espacial da biomassa microfitobentônica no perfil batimétrico da região de Ubatuba, SP." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/21/21134/tde-10022015-113340/.
Full textAbstract:
O microfitobentos é constituído principalmente por diatomáceas, além de fitoflagelados e cianobactérias, distribuindo-se de forma heterogênea no sedimento exposto à luminosidade. O objetivo deste estudo foi avaliar a distribuição espacial da biomassa microfitobentônica no perfil batimétrico da região de Ubatuba, SP. As amostras foram coletadas no verão de 2013, em três transectos (Flamengo, Fortaleza e Mar Virado), com seis pontos cada, coletadas entre as isóbatas de 5 e 30 m. A biomassa foi expressa como clorofila a. Clorofila a e feopigmentos foram extraídos com acetona e medidos em espectrofotômetro. Os valores médios dos pigmentos foram de 18,5 ± 11,4 mg.m-2 para clorofila a e de 28,4 ± 16,2 mg.m-2 para feopigmentos no transecto do Flamengo; de 11,9 ± 10,2 mg.m-2 para clorofila a e de 18,8 ± 15,2 mg.m-2 para feopigmentos no transecto do Mar Virado; e de 11,8 ± 11,3 mg.m-2 para clorofila a e de 13,7 ± 13,6 mg.m-2 para feopigmentos no transecto da Fortaleza. Estes valores foram maiores nas regiões mais rasas. A distribuição da biomassa foi associada positivamente com intensidade de luz, silte, argila, matéria orgânica e carbono orgânico total, enquanto foi correlacionada negativamente com profundidade, areia e grânulos.Marine microphytobenthos community is composed mainly by diatoms and also phytoflagellates and cyanobacteria, which cover the marine sediments submitted to light. This study aims to survey the spatial distribution of bathymetric profile microphytobenthic biomass in Ubatuba region, SP. The samples were collected in the summer (March, 2013), at three transects: Flamengo, Fortaleza and Mar Virado, with 6 points each, between the isobaths of 5 and 30 meters. The biomass was expressed as chlorophyll a. Chlorophyll a and phaeopigments were extracted with acetone and measured at spectrophotometer. The biomass averages values were: chlorophyll a 18,5 ± 11,4 mg.m-2 and phaeopigments 28,4 ± 16,2 mg.m-2 for Flamengo transect; chlorophyll a 11,9 ± 10,2 mg.m-2 and phaeopigments 18,8 ± 15,2 mg.m-2 for Mar Virado transect; and chlorophyll a 11,8 ± 11,3 mg.m-2 and phaeopigments 13,7 ± 13,6 mg.m-2 for Fortaleza transect. Chlorophyll a and phaeopigments averages values were higher in the shallow regions. The biomass distribution was positively associated to light intensity, silt, clay, total organic carbon and organic matter. Negative correlations were found for depth and coarse grains.
42
Heijden, Luuk van der [Verfasser]. "Determination of the food sources and of the role of meiofauna in soft-bottom intertidal habitats of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany. Importance of the microphytobenthos-meiofauna pathway, highlighted by community structure, trophic markers and linear inverse food web models. / Luuk van der Heijden." Kiel : Universitätsbibliothek Kiel, 2019. http://d-nb.info/1191179826/34.
Full text
43
Polsenaere, Pierre. "Echanges de CO2 atmosphérique dans la lagune d’Arcachon et relations avec le métabolisme intertidal." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14253/document.
Full textAbstract:
Les zones côtières ne sont prises en compte dans les budgets globaux de CO2 atmosphérique que depuis peu. Il s’avère que bien qu’elles ne représentent globalement que de faibles superficies, les flux de carbone et de nutriments y sont très significatifs à l’échelle globale. On sait peu de chose sur le comportement des écosystèmes lagunaires vis-à-vis du CO2 et, encore moins des zones intertidales où les échanges avec l’atmosphère ont lieu alternativement avec l’eau et le sédiment. Les objectifs de cette étude ont été d’une part, d’établir le bilan de carbone échangé entre la lagune d’Arcachon, l’atmosphère et le milieu terrestre, et d’autre part de mettre en relation ces flux avec la production nette de l’écosystème (NEP) afin de mieux caractériser le statut métabolique de celle-ci ainsi que les facteurs environnementaux clés. Pour cela, nous avons mis en place pour la première fois et à différentes saisons et stations, des mesures directes de flux de CO2 par Eddy Corrélation, une méthode fonctionnant en continu pendant l’immersion et l’émersion. En parallèle, les apports de carbone terrestre sous ses différentes formes ont été quantifiés par un suivi annuel sur 9 rivières alimentant la lagune. L’export total de carbone par le bassin versant à travers les eaux de surface des rivières est estimé à 116 t C km-2 an-1 dont 39% est exporté à la lagune sous forme organique dissoute (DOC) du fait de la prédominance de podzols dans le bassin versant. La forte minéralisation de la matière organique terrestre dans les sols et eaux souterraines sursature largement les eaux en CO2 et l’export sous forme de carbone inorganique dissoute (DIC) représente environ 21%. La formulation d’un modèle mathématique, le « StreamCO2-DEGAS », basé sur les mesures de pCO2, de concentrations et de compositions isotopiques en DIC a permis de montrer que 43% de l’export total de carbone était dégazé sous forme de CO2 depuis les rivières vers l’atmosphère, réduisant alors le flux net entrant dans la lagune à 66 t C km-2 an-1. Concernant la mesure de flux verticaux, l’analyse cospectrale ainsi que les résultats obtenus en adéquation avec les contrôles physiques et biologiques aux différentes échelles tidale, diurne et saisonnières, ont permis de valider la méthode de l’Eddy Covariance en zone intertidale. Sur l’ensemble de la période de mesures, les flux de CO2 étaient faibles, variant entre -13 et 19 µmol m-2 s-1. Des puits de CO2 atmosphérique à marée basse le jour ont été systématiquement observés. Au contraire, pendant l’immersion et à marée basse la nuit, des flux positifs ou négatifs ou proche de zéro ont été observés suivant la saison et la station étudiées. L’analyse concomitante des flux de CO2 et des images satellites du platier à marée basse le jour a clairement permis de discriminer l’importance relative des deux cycles métaboliques distincts des principaux producteurs primaires avec (1) les herbiers de Zostera noltii à cycle annuel long, dominant la NEP en été et en automne à la station la plus centrale et (2) les communautés microphytobenthiques, dominant la production primaire brute (PPB) au printemps à la même station et en automne au fond du bassin. Un recyclage rapide de cette production durant l’immersion et l’émersion a aussi clairement été mis évidence. Au vue des différents résultats, la technique d’Eddy Covariance utilisée en zone intertidale laisse envisager d’intéressantes perspectives en termes de connaissances sur les budgets de carbone et les processus écologiques et biogéochimiques dans la zone côtièreThe coastal zone is only taken into account since recently in global carbon budgeting efforts. Although covering globally modest surface areas, carbon and nutrient fluxes in the coastal zone appear significant at the global scale. However, little is known about the CO2 behaviour in lagoons and even less in intertidal zones where exchanges with the atmosphere occur alternatively with the water and the sediment. The purposes of this work are, on one hand, to establish the carbon budget between the Arcachon lagoon, the atmosphere and the terrestrial watershed and on the other hand, to link these fluxes with the net ecosystem production (NEP) and better characterize its metabolic status along with the relevant environmental factors. For the first time, CO2 flux measurements by Eddy Correlation have been carried out at different seasons and stations in the tidal flat. In parallel, the total terrestrial carbon export from river waters has been quantified throughout a complete hydrological cycle in nine watercourses flowing into the lagoon. The total carbon export from the watershed through surface river waters is estimated at 116 t C km-2 yr-1 on which 39% is exported to the lagoon as dissolved organic carbon (DOC) owing to the predominance of podzols in the watershed. Intense organic matter mineralization in soils and groundwaters largely over-saturate river waters in CO2 on which export accounts for 21% as dissolved inorganic carbon (DIC). The mathematical “StreamCO2-DEGAS” model formulation based on water pCO2, DIC concentrations and isotopic composition measurements permits to show that 43% of the total carbon export was degassed as CO2 from the riverine surface waters to the atmosphere, lowering then this latter to 66 t C km-2 yr-1. With respect to the CO2 flux measurements in the lagoon, cospectral analysis and the well accordance of results with physical and biological controls at the tidal, diurnal and seasonal time scales permit to validate the Eddy Correlation technique over tidal coastal zone. CO2 fluxes with the atmosphere, during each period, were generally weak and ranged between -13 and 19 µmol m-2 s-1. Low tide and daytime conditions were always characterized by an uptake of atmospheric CO2. In contrast, during the immersion and during low tide at night, CO2 fluxes where either positive or negative, or close to zero, depending on the season and the site. The concomitant analysis of CO2 fluxes with satellite images of the lagoon at low tide during the day clearly discriminate the relative importance of the two distinct metabolic carbon cycling involving the main primary producers, i.e. (1) the Zostera noltii seagrass meadow predominance on the NEP in autumn and summer in the more central station, with an annual cycling and (2) the microphytobenthos community predominance on the gross primary production (GPP) in spring at the same station and in autumn in the inner part of the bay where a rapid carbon cycling during the immersion and the emersion was clearly highlighted. The different results obtained with the Eddy Correlation technique over tidal flats opens interesting perspectives on the knowledge of the carbon budget and the biogeochemical and ecological processes within the coastal zone
44
Pivato, Mattia. "Water and Sediment Temperature Dynamics in Shallow Tidal Environments." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427269.
Full textAbstract:
The purpose of the present study is to investigate the water and sediment temperature dynamics in shallow coastal environments. Indeed, water and sediment temperature dynamics are a first order control of many physical and biological processes in aquatic ecosystem, driving the short and long term evolution of the ecosystem.
Given the scarcity of studies and data from the literature that investigate in particular the heat fluxes at the sediment-water interface (SWI), we conceived and performed an ad hoc, one-year-long field campaign was performed in the Venice lagoon to collect water and sediment temperature data. The collected data show that, in our study site, temperature is uniform within the water column, and enabled us to estimate the net heat flux at the sediment-water interface. Based on these results we developed a "point" model for describing the temperature dynamics of the sediment-water continuum in shallow tidal environments. Modeling the flux at the SWI as the sum of a conductive component and of the solar radiation reaching the bottom, we found the latter being negligible. Our analysis further revealed that, in general, horizontal advection driven by tidal currents is an important process also at our study site despite we placed it quite close to a divide. For applying the "point" model we therefore selected, in our data set, only periods when advection is negligible, that correspond to periods characterized by neap tide and small temperature difference between sea and lagoon. The results we obtained following our numerical approach are quite satisfactory showing the capability of the model of reproducing, in the selected conditions, the temperature dynamics both in the water column and within the sediments. Both the analysis of the data and model results show that the heat exchange between water and sediment is crucial for describing sediment temperature but plays a minor role on the water temperature. This observation suggests that, as a first approximation, the water temperature dynamics can be modeled neglecting the heat exchange between water and sediments.
Using the developed numerical model we further investigated the effect of different turbidity conditions of the water column on the water and sediment temperature and on the photosynthetic capacity of the microphytobenthos (MPB), i.e. communities of microalgae commonly present in coastal environments and colonizing the uppermost layer of bed sediments. We found that the water temperature dynamics is poorly affected by the different conditions investigated, while the sediment temperature variation is significant, especially for very shallow water depth (i.e. ≤0.5 m). Considering the average annual budget, the photosynthetic rate of the MPB is found to be better promoted by clear water conditions, being the light availability the major limiting factor for the photosynthetic process. These results suggest the possibility of investigating a positive feedback between water column turbidity and the MPB proliferation, driven by its photosynthetic capacity. In fact, the abundance of MPB provides a bio-stabilization of the sediment bottom, creating a biofilm that limits sediment resuspension and thus reduces the water column turbidity.Lo scopo della presente ricerca è di studiare la dinamica della temperatura dell'acqua e dei sedimenti in ambienti costieri poco profondi. La temperatura dell'acqua e dei sedimenti è certamente uno dei fattori più importanti per numerosi processi fisici e biologici che determinano l'evoluzione a breve e lungo termine degli ambienti acquatici. In letteratura si trovano pochi dati e pochi lavori che analizzano nello specifico i flussi di calore all’interfaccia sedimenti-acqua (SWI). Abbiamo quindi pianificato e realizzato una campagna di misura ad hoc della durata di un anno in laguna di Venezia al fine di raccogliere dati di temperatura dell’acqua e del fondale. L'analisi dei dati ha mostrato che, nel sito da noi considerato, la temperatura si può assumere distribuita uniformemente nella colonna d'acqua. I dati sono stati quindi utilizzati per stimare il flusso di energia all'interfaccia tra acqua e fondale. Sulla base di questi risultati, abbiamo sviluppato un modello ``puntuale'' per descrivere la dinamica del profilo verticale di temperatura nel continuo acqua-sedimento in ambienti a marea caratterizzati da bassi fondali. Modellando il flusso di energia al fondo come la somma di una componente conduttiva e della radiazione solare residua al fondo, si è osservato che la seconda risulta essere trascurabile. I risultati ottenuti mostrano inoltre che il trasporto orizzontale di calore legato alle correnti di marea, e pertanto l'applicabilità del modello ``puntuale'', è limitata ai periodi caratterizzati da condizioni tali da limitare l'avvezione (i.e. marea di quadratura e/o poca differenza tra la temperatura dell'acqua in mare e all'interno della laguna). I risultati forniti dal modello per periodi caratterizzati da avvezione trascurabile sono soddisfacenti. Sia l’analisi dei dati che i risultati forniti dal modello mostrano che lo scambio di calore tra acqua e fondale è di cruciale importanza per descrivere la temperatura dei sedimenti, mentre risulta trascurabile per la dinamica della temperatura dell’acqua. Questo suggerisce che, in prima approssimazione, la dinamica della temperatura della colonna d’acqua può essere modellata trascurando lo scambio di calore tra acqua e sedimenti. L'applicazione del modello ad una condizione sintetica ha quindi permesso di analizzare l'effetto di diverse condizioni di torbidità della colonna d'acqua sulla dinamica della temperatura della colonna d'acqua stessa e dei sedimenti al fondo, e quindi sulla capacità fotsintetica del microfitobentos, i.e. comunità di micro-alghe tipicamente presenti in ambienti costieri. I risultati mostrano che la dinamica della temperatura dell'acqua risente poco delle diverse condizioni di torbidità, mentre la temperatura dei sedimenti al fondo varia in modo significativo, soprattutto per fondali particolarmente bassi (i.e. ≤ 0.5 m). La capacità fotosintetica del microfitobentos, considerando l'andamento medio a scala annuale, risulta favorita dal condizioni acqua limpida, in quanto la disponibilità di luce al fondo risulta essere il principale fattore limitante per la fotosintesi. I risultati suggeriscono quindi la possibilità di indagare l'esistenza di un possibile feedback positivo tra torbidità della colonna d'acqua e proliferazione del microfitobentos, chiaramente legata alla sua capacità fotosintetica. Il microfitobentos infatti produce un biofilm che, se presente in quantità rilevanti, ha un effetto di bio-stabilizzazione del fondale che limita l'erosione e la risospensione dei sedimenti, e quindi una potenziale riduzione della torbidità dell'acqua.
45
De, Crignis Margot. "Déterminisme de la production bactérienne dans les vasières intertidales du Bassin de Marennes-Oléron : rôle des exopolysaccharides." Phd thesis, Université de La Rochelle, 2010. http://tel.archives-ouvertes.fr/tel-00605659.
Full textAbstract:
Les vasières intertidales sont le siège d'une forte production primaire sous la forme d'un biofilmmicrophytobenthique qui se développe en surface à marée basse. Ce biofilm se compose principalement de diatomées et de bactéries hétérotrophes. Ces deux composantes sécrètent des substances polymériques extracellulaires (EPS) qui jouent différents rôles dans le biofilm. Le travail présenté s'est basé sur différentes échelles d'observation (in situ à 2 saisons, mésocosme en laboratoire, et échelle fine du biofilm en microscopie confocale) et a permis de mettre en évidence les interactions des diatomées et des bactéries à différents moments de la marée et du nycthémère. L'utilisation d'une nouvelle méthode d'extraction des EPS a permis d'éclaircir leur rôle en évitant les contaminations par les substances internes provoquées par les méthodes classiques. Les EPS colloïdales particulièrement riches en glucose s'associent au déplacement des diatomées, notamment lors d'un stress (sursalure, carence en nutriments) et sont préférentiellement consommées par les bactéries, après leur dégradation par les enzymes ou leur hydrolyse dans l'eau interstitielle. Les EPS liées au frustule, et plus particulièrement les sucres, inhiberaient le développement bactérien à proximité de la cellule algale. Elles sont surtout sécrétées lors de la mise en place du biofilm et pour protéger la cellule quand les conditions sont osmotiquement défavorables et leur richesse en protéine leur confère un potentiel intéressant pour les bactéries qui peuvent les utiliser comme substrat azoté en cas de carence. D'autres substances ont été plutôt sécrétées parles bactéries telles que les N-acétylglucosamines et les protéines colloïdales de bas poids moléculaire,certainement des enzymes bactériennes, ainsi que le glucose qui semble être associé au EPS colloïdaux des diatomées mais aussi aux EPS bactériens selon l'analyse en microscopie confocale en utilisant des lectines comme marqueurs d'EPS.
46
Jordan, Leonie Jane. "The survival strategies of microphytobenthos : behaviour and physiology." Thesis, 2009. https://eprints.utas.edu.au/20704/1/whole_JordanLeonieJane2009_thesis.pdf.
Full textAbstract:
Microphytobenthos (MPB) need photoadaptive strategies to survive the highly
dynamic light environment in which they reside. They are able to adjust their
photosynthetic activity by physiological regulation or behaviourally by migrating
vertically through the sediment. This study investigates the effects of the time of day on
the vertical migration of benthic diatoms at two sites near Hobart, Tasmania using a pulse
amplitude modulation fluorometer (Water PAM; Walz, Effeltrich) to measure chlorophyll
fluorescence. Chlorophyll a content and maximum quantum yield (Fv/Fm) were used to
examine the profiles of microalgal biomass and photosynthetic properties within
sediment cores, both diurnally and over a 12 month experimental period. The results
show a seasonal pattern of chlorophyll a biofilm development, with maximum values
attained in summer at Pipe Clay Lagoon and in spring at Browns River. A greater amount
of biomass was observed in the muddier sediment at Browns River with a sharper peak of
chlorophyll a compared to the gradual incline then decline at Pipe Clay Lagoon. Fv/Fm
values changed throughout the day with the cells more quenched at midday than sunrise
while experiencing the highest illumination.
Xanthophylls can provide photoprotection to MPB cells by cycling between
epoxide and de-epoxide forms to dissipate excess light energy as heat. The second part of
the study examined the xanthophyll cycle in microphytobenthos on tidally exposed
sediment at Browns River. The goal of this work was to examine whether
microphytobenthos at Browns River used the xanthophyll cycle as a physiological
defence against photoinhibition during a natural light-dark cycle (day-night). A High
Pressure Liquid Chromatography (HPLC) system was used as a pigment separation
technique followed by pigment detection using a photodiode array and quantification
against pure pigment standards. A pulse amplitude modulated (PAM) fluorometer was
used to determine the chlorophyll fluorescence and assess photosynthetic performance in
terms of maximum PSII quantum yield (Fv/F,,,), non-photochemical quenching and Ek in
the field. Changes in PAM fluorescence and xanthophyll: chlorophyll a ratios suggests
that MPB were under physiological stress at noon. The results indicate that the MPB cells
exposed to light at the surface migrated deeper into the •sediments to replenish the epoxide form of their xanthophylls. Overall the result suggests that MPBs utilise both
behavioural and physiological strategies to survive in the dynamic intertidal environment.
This research highlights the importance of the photoadaptive strategies of MPB in
a changing light environment with particular reference to the need for more than one
strategy. This research on MPB ecology helps to form a more accurate picture on survival
strategies while it underlines the fact that previous research has shown inconsistencies.
Further research is needed in this area, particularly in the southern hemisphere, to lessen
these inconsistencies and build on current knowledge.
47
Ruivo, Michael Philippe Marquês 1986. "Characterization by HPLC of phytoplankton and microphytobenthos photosynthetic pigments." Master's thesis, 2010. http://hdl.handle.net/10451/2415.
Full textAbstract:
Tese de mestrado. Biologia (Ecologia Marinha). Universidade de Lisboa, Faculdade de Ciências, 2010As zonas costeiras são regiões de enorme produtividade, demonstrando elevada diversidade de organismos de fitoplâncton e de microfitobentos. A biomassa e produção destes organismos autotróficos são afectadas, entre outros factores, pela disponibilidade de luz e nutrientes. As clorofilas, carotenóides e ficobilinas são os principais tipos de pigmentos fotossintéticos, sendo essenciais à fotossíntese. A cromatografia líquida de alta precisão (HPLC) é uma técnica que permite a análise qualitativa e quantitativa dos vários pigmentos fotossintéticos, disponibilizando informações acerca de biomassa, composição e estado fisiológico das comunidades de fitoplâncton e de microfitobentos. Capítulo 2 Neste capítulo estudaram-se os efeitos das fases de crescimento, exponencial e estacionária, e da irradiância nas concentrações e razões pigmentares em espécies fitoplanctónicas. No estudo do efeito da fase de crescimento foram utilizadas sete espécies, entre elas dois dinoflagelados, Amphidinium carterae e Gymnodinium catenatum, uma clorofícea, Dunaliella salina, uma prasinofícea, Tetraselmis suecica, duas diatomáceas, Cylindrotheca closterium e Phaeodactylum tricornutum, e uma criptofícea, Rhodomonas sp. Após realização das curvas de crescimento, amostraram-se três réplicas em fase exponencial e três réplicas em fase estacionária. No estudo do efeito da irradiância nas concentrações e razões pigmentares usaram-se 3 espécies, A. carterae, C. closterium e T. suecica, submetidas a três níveis de irradiância (Luz Baixa, LL = 10 μmol fotões m-2 s-1; Luz Média, ML, 100 μmol fotões m-2 s-1; Luz Alta, HL, 400 μmol fotões m-2 s-1). Amostraram-se três réplicas em fase exponencial para cada nível de irradiância. A análise e caracterização pigmentar das várias espécies foi efectuada por HPLC. A comparação entre as fases de crescimento exponencial e estacionária demonstrou a existência de diferenças significativas tanto nas concentrações como nas razões pigmentares. As concentrações de pigmentos fotossintéticos por célula (e.g. clorofila a, clorofila b, fucoxantina e neoxantina) foram superiores durante a fase de crescimento exponencial. Tais resultados podem ser consequência da limitação de nutrientes e/ou da idade celular durante a fase estacionária. Por sua vez, obtiveram-se, consistentemente, maiores concentrações de anteraxantina, diatoxantina e zeaxantina durante a fase estacionária, demonstrando que pigmentos tipicamente com função fotoprotectora tendem a aumentar a sua concentração quando as células entram nesta fase, provavelmente devido ao seu envolvimento na prevenção foto-oxidativa das células. Os ratios pigmento/clorofila a, (exceptuando a violaxantina e o β-Caroteno), violaxantina + anteraxantina + zeaxantina (VAZ)/clorofila a e diadinoxantina + diatoxantina (DD + DT)/clorofila a e os índices de de-epoxidação (DPS) foram sistematicamente superiores durante a fase estacionária. Verificaram-se diferenças inter-específicas para espécies pertencentes ao mesmo grupo taxonómico. Em C. closterium a razão fucoxantina/clorofila a não variou significativamente enquanto em P. tricornutum esta razão foi aproximadamente o dobro na fase estacionária. Nos dinoflagelados, a razão peridinina/clorofila a aumentou menos de 25% entre as fases exponencial e estacionária, todavia essas diferenças só foram significativas em A. carterae. O efeito da irradiância foi significativo nas concentrações dos pigmentos de colheita de luz (LHP) e pigmentos fotoprotectores (PP). As maiores concentrações de LHP ocorreram em LL, intermediárias em ML e finalmente mais baixas em HL. Esta diminuição na concentração de LHP com o aumento da intensidade luminosa é devido à fotoaclimatação das células regulada pelo tamanho das antenas fotossintéticas. Pelo contrário, os PP apresentaram maiores concentrações em HL e menores em LL. A de-epoxidação de violaxantina em anteraxantina e zeaxantina e de diadinoxantina em diatoxantina (ciclo das xantofilas), regula o excesso de energia, consequência do aumento da irradiância, através da dissipação de calor, permitindo a protecção do aparelho fotossintético. Genericamente, as razões de pigmentos com função fotossintética, e embebidos nos complexos de colheita de luz, foram constantes nas diferentes irradiâncias, pois tendem a co-variar com a clorofila a. No entanto, as razões de pigmentos com função protectora foram superiores em HL (e.g. luteína e zeaxantina). No capítulo considerado demonstrou-se o efeito significativo da fase de crescimento e da luz nas razões pigmento/clorofila a. Assim sendo, estas variáveis devem ser consideradas na aplicação dos pigmentos fotossintéticos como indicadores quimiotaxonómicos para o estudo de comunidades fitoplanctónicas. Capítulo 3 Os objectivos deste estudo foram direccionados para a comparação da fotoprotecção fisiológica (utilização dos ciclo das xantofilas como forma de dissipação do excesso de energia no aparelho fotossintético) e comportamental (capacidade de migração vertical que permite às microalgas o controlo do nível de irradiância a que estão expostas) entre comunidades epipélicas e epipsâmicas de substrato vazoso e arenoso no estuário do Tejo. Amostraram-se dois locais: um tipicamente constituído por partículas de dimensões inferiores a 63 μm (denominado vasa), e outro com partículas de calibre entre 125 e 1000 μm (referido como areia). Assim sendo, aspectos como fluorescência, atenuação da luz, curvas rápidas de luz, análise e caracterização pigmentar e avaliação da capacidade migratória foram estudados recorrendo a técnicas de fluorescência de Pulso Modulado (PAM) e HPLC. Na comparação entre as comunidades epipélicas e epipsâmicas verificaram-se diferenças nos diversos parâmetros estudados. Na comunidade de substrato vazoso, denotou-se um efeito da profundidade nos perfis de clorofila a e uma diminuição da concentração de clorofila a ao longo do perfil. O coeficiente de atenuação da luz (k) foi elevado, com um decréscimo na disponibilidade da luz para 33%, 7% e 1% da luz incidente à superfície a profundidades de 200, 400 e 600 μm, respectivamente. Na comunidade de substrato arenoso, não se verificaram diferenças significativas nas concentrações de clorofila a, sendo estas constantes ao longo do perfil. O coeficiente de atenuação de luz foi inferior, comparativamente ao valor obtido no substrato vazoso, com 80%, 50% e 2% de disponibilidade de luz a profundidades, de 200 μm, 400 μm e 3000 μm, respectivamente. As diferenças de k e da concentração de clorofila a ao longo dos perfis de sedimento são devido ao tamanho das partículas, provocando assim, uma diferenciação na distribuição vertical das comunidades bênticas. O calibre das partículas de sedimento e k variam de forma inversamente proporcional. Em substrato vazoso, ocorreu uma diminuição de clorofila a à superfície (0-200 μm) no controlo sob luz alta (Cont HL) quando comparado com luz baixa (LL) e sedimentos tratados com um inibidor de motilidade (Lat A HL). Em simultâneo, observou-se um aumento da percentagem relativa de clorofila a na camada de 200-400 μm. Tal situação, não se verificou em Lat A HL devido à presença do inibidor de motilidade, prevenindo a migração. Estes resultados indicam que as diatomácias epipélicas da vasa submetidas a luz forte migram em profundidade – fotoprotecção comportamental – e corrobora a função de Lat A como um inibidor altamente específico de motilidade em diatomácias. Ambas comunidades estudadas activaram mecanismos fisiológicos de fotoprotecção quando sujeitas a luz forte. No substrato vazoso o índice DPS foi superior em Lat A HL quando comparado com LL (estrato 0-200 μm), mas sem diferenças significativas entre Lat A HL e Cont HL. No substrato arenoso o índice DPS foi inferior para LL, intermédio para Cont HL e superior em Lat A HL. Estes resultados indicam diferenças significativas com Cont HL. A interpretação destes resultados sugere que as comunidades pertencentes aos substratos vazoso e arenoso recorrem ao ciclo das xantofilas como mecanismo de fotoprotecção, independentemente da sua capacidade migratória. Na avaliação da influência dos diferentes tratamentos nos vários parâmetros das curvas rápidas de resposta-luz (taxa máxima relativa de transporte de electrões -rETRmax; declive inicial da taxa fotossintética não saturada - α; parâmetro de saturação de luz - Ek) denota-se um efeito significativo dos vários tratamentos, para ambos substratos em rETRmax, α e Ek. A excepção ocorre no substrato arenoso para Ek, onde não existem diferenças significativas. Porém, no substrato vazoso, os valores de rETRmax, α e Ek foram significativamente mais baixos em Lat A HL que em Cont HL enquanto essas diferenças não foram significativas no substrato arenoso. Estes resultados são consequência das diferentes condições de luz na matriz sedimentar dos substratos estudados, e provavelmente devido a diferenças na composição taxonómica. Este trabalho demonstra as diferentes respostas das células às variações de luz no sedimento: i) através de fotoprotecção fisiológica (ciclo das xantofilas) e/ou ii) movimento vertical descendente ao longo do perfil de sedimento, denominado fotoprotecção comportamental. As comunidades epipélicas, por apresentarem capacidade migratória, utilizam tanto a fotoprotecção fisiológica como comportamental, enquanto as comunidades epipsâmicas, sem capacidade migratória, valem-se apenas de fotoprotecção fisiológica.
Phytoplankton and microphytobenthos communities influence coastal systems productivity and are affected, among other factors, by light and nutrients availability. Growth phase and light variation effect on phytoplankton pigment concentrations and physiological vs. behavioral photo-protection of epipelic and epipsamic microphytobenthos communities were studied using High Performance Liquid Chromatography. Growth phase and light variation showed a significant effect on phytoplankton light harvesting (LHP) and photo-protective (PP) pigments. LHP concentrations were lower during stationary growth phase presumably by nutrient limitation and cellular age whereas photo-protective pigments increased. An increment of pigment ratios from exponential to stationary phase was consequence of the pronounced decrease in chlorophyll a cellular content comparatively with other pigments. Light increase lead to a decrease on photosynthetic pigment concentrations due to cellular photoacclimation, while the photo-protective pigment concentrations increase, allowing the dissipation of excess energy. This study shows that growth phase and light intensity have significant effects on pigment/Chl a ratios, including many marker pigments, and this should be taken into account in the application of chemotaxonomical approaches to phytoplankton natural communities. Microphytobenthos biomass vertical distribution in intertidal mud and sandflats of the Tagus estuary was considerably different depending on the type of sediment. In the mud, a steep decrease in biomass accumulation from the surface down to 1 mm was observed, whereas in the sand Chl a concentrations were relatively stable throughout the profile. Epipelic and epipsamic communities showed different photo-regulaton strategies: both communities photo-regulated using physiological photo-protection while the epipelic community of muddy sediments used physiological and behavioral photoprotection.
48
Vieira, Sónia Catarina Reis 1978. "Photosynthetic metabolism in microphytobenthos : modulation by temperature and dissolved inorganic carbon." Doctoral thesis, 2016. http://hdl.handle.net/10451/30278.
Full textAbstract:
Tese de doutoramento, Biologia (Ecofisiologia), Universidade de Lisboa, Faculdade de Ciências, 2017Main primary producers of estuarine systems include benthic microalgae, predominantly diatoms, and cyanobacteria that colonize subtidal and intertidal zones, commonly referred to as microphytobenthos (MPB). MPB communities account for about 50% of the primary productivity of estuarine systems (e.g. MacIntyre et al., 1996; Barranguet et al., 1998; Underwood and Kromkamp, 1999; Serôdio and Catarino, 2000). This is highly relevant considering that estuarine systems are among the most productive ecosystems in the biosphere (Constanza et al., 1997). Despite the extreme variability of environmental parameters (irradiance, temperature and salinity) that characterizes the estuarine habitat, these communities are able to display high photosynthetic rates. It is common to distinguish two types of MPB communities: epipelic communities (typical of muddy sediments) composed of motile species and epipsammic communities (typical of sandy sediments) composed largely by non-motile species attached to sand grains. Contrary to epipsammic, epipelic diatoms exhibit circadian and circatidal migratory rhythms (Palmer and Round, 1967; Palmer, 1973; Admiraal et al., 1982; Serôdio and Catarino, 2000). Being MPB critical for the function of estuarine and coastal ecosystems, understanding the impact of climate change on its structure and productivity is mandatory. In particular, the increase of temperature and inorganic carbon availability can markedly affect photosynthesis, diversity and productivity of estuarine MPB communities. However, studies of the impact of climate changes on MPB are still scarce, and in particular the effects of the interaction between increased temperature and inorganic carbon availability are, to a large extent, still unknown. Thus, in this project we studied the effects of temperature and dissolved inorganic carbon (DIC) availability in two MPB communities of the Tagus estuary, in central Portugal, applying new methods of remote sensing, namely laser induced fluorescence (LIF) and modulated imaging fluorescence (Imaging-PAM). The LIF methodology (chapter 2) was used to trace migratory rhythms of benthic epipelic microalgae typical of mud sediments. Indeed, it was confirmed that, during the diurnal low tide these microalgae migrate to the surface of sediment to drive photosynthesis and then migrate in depth before the arrival of the tide. Furthermore, epipelic diatoms show photophobic migration when exposed to high light levels, a process known as behavioral photoprotection. This technique proved to be adequate to the study of MPB communities, both for the determination of surface biomass and the study of migratory rhythms. The possibility of using LIF for middle-range remote sensing under natural light conditions opens good perspectives for its use in environmental monitoring of estuarine systems. In the last decades, conventional pulse amplitude modulated fluorescence (PAM) has been increasingly applied to estuarine MPB communities (Serôdio et al., 1997; Kromkamp et al., 1998; Paterson et al., 1998; Serôdio et al., 2001; Honeywill et al., 2002; Perkins et al., 2002; Serôdio, 2003; Stephens et al., 2003; Forster and Kromkamp, 2004; Murphy et al., 2004; Serôdio, 2004; Forster and Jesus, 2005; Murphy et al., 2005). Lower resolution imaging systems allow the mapping of fluorescence parameters over large areas, making it a unique technique to study the spatial heterogeneity of the photosynthetic activity across an autotrophic surface (Scholes and Rolfe, 1996; Hill et al., 2004. This can be particularly relevant in the study of MPB biofilms, characterized by a “patchy,” heterogeneous distribution and can provide useful information about the spatial distribution of biomass and productivity in sediments. Yet, important hardware differences exist between conventional and imaging systems and therefore a comparative study of the results obtained with these technologies in MPB was required (chapter 3). In fact, we observed significant differences between the results obtained with conventional and imaging systems, especially in what refers to the analysis of rapid fluorescence curves as a function of irradiance (RLCs, Rapid Light Curves). Lower values of α (initial slope of the rETR vs. E curve), ETRmax (maximum relative ETR), Ek (light saturation parameter) and Fv/Fm (maximum quantum efficiency of photosystem II of dark-adapted samples) were obtained using the Imaging- PAM system. The discrepancy between instruments was dependent on sample type, being more pronounced in mud than in sandy MPB sediments. The differences may be largely explained by the interplay between the different depth-integration of the fluorescence signal, dependent on the thickness of the photosynthetic layer, and the different attenuation coefficients of the light sources used by the two types of instrument. It is therefore important to take into account the specificity of each fluorescence system when interpreting and comparing chlorophyll fluorescence data of MPB communities, taking full advantage of the application of imaging fluorescence to the MPB communities, in particular in what refers to its unique ability to study the spatial heterogeneity of their photosynthetic activity. The in-depth understanding of the primary production processes of MPB is a prerequisite to assess the impacts of climate change on estuarine systems. Among the global change variables, increased temperature and atmospheric CO2 (and concomitantly dissolved inorganic carbon, DIC) are expected to have the most significant impact over the primary productivity in estuaries. Therefore, we studied their effect, as well as their interaction, on the photosynthesis of MPB biofilms. The short-term effect of increasing temperature in the photosynthetic activity of two communities of MPB (Alcochete and Trancão) was studied (chapter 4). The Trancão MPB community had higher photosynthetic electron transport capacity (higher ETRmax) being photoacclimated at higher irradiance (higher EK) and had lower energy conversion efficiency at limiting irradiance (lower α) .The differences in the species composition and size class may explain the results obtained for the two sites, since smaller cells are generally more metabolically active. However, for the both MPB communities photosynthetic capacity increased with temperature up to 35 °C and decreased with extreme temperature of 42 °C. Photosynthetic efficiencies at low irradiance (α) were not affected by the temperature in the 15-35 °C range, and decreased at 42 °C. These MPB estuarine communities were able to increase the photosynthetic capacity under exposure to short-term high temperatures sediments, similar to happens during the summer midday in the diurnal low tides. We also studied the effect of dissolved inorganic carbon availability (DIC) in photosynthesis, on the two intertidal MPB communities, taking as reference the model diatom species Phaeodactylum tricornutum, using fluorescence imaging (on intact MPB communities) and polarographic oxygen measurement (in cell suspensions) (chapter 5). The parameters of DIC acquisition kinetics (Vmax and Km (DIC)) estimated for MPB communities were higher ((Km (DIC) = 0.31 mM; Vmax = 7.78 nmol min-1 μg (Chl a)-1), than those obtained for Phaeodactylum tricornutum (Km (DIC) = 0.23 mM; Vmax = 4.64 nmol min-1 μg (Chl a)-1), showing that these communities have species with low affinity for DIC and high photosynthetic capacity. The net photosynthesis of MPB suspensions reached saturation at DIC concentrations of 1-1.5 mM, 17 lower than those found in the sediment top 5 mm interstitial water, suggesting that the photosynthesis of these communities is not limited by DIC availability. However, when NaHCO3 was added to intact MPB samples, an increase in the maximum photosynthetic electron transport rate (ETRmax) was observed. These results suggest that the local depletion of DIC in the photic layer of the sediment, where the microalgae accumulate during diurnal low tide, limits the photosynthetic activity of MPB, providing the first experimental evidence of DIC limitation of the productivity of intertidal MPB communities. The interactive effects of temperature and DIC in biomass, species composition and photosynthetic performance of MPB was studied using a microcosm ELSS ('experimental life support system') with tide regime (chapter 6). The longer term effect of increased temperature (24 ° C) had a negative effect on MPB biomass and photosynthetic performance under both simulated DIC conditions (pH = 7.4 and pH = 8.0). Furthermore, at elevated temperatures there was a change in the relative abundance of the major species of diatoms and an increase of cyanobacteria. The long term effect of increasing DIC ( pH = 7.4) under low temperature (18 °C) had a positive effect on biomass MPB, possibly due to decreased local depletion of dissolved inorganic carbon. No significant effects were found on the relative abundance of the major groups of microalgae. Our results suggest that the interactive effects of increased temperature and DIC availability of estuarine MPB communities can have a negative impact on the structure, diversity and productivity of these communities, eventually affecting the entire estuarine ecosystems. Therefore, a deepen understanding of the potential impacts of climate change in these complex ecosystems is required.
49
Iyer, Kogilam. "The dynamics of microphytobenthos in the Mdloti and Mhlanga estuaries, Kwazulu-Natal." Thesis, 2004. http://hdl.handle.net/10413/2370.
Full textAbstract:
Microphytobenthos (MPB) generally dominates total autotrophic biomass in temporarily open/closed estuaries (TOCEs) of South Africa. A comparative study of MPB biomass was undertaken in two KwaZulu-Natal TOCEs, the Mdloti and the Mhlanga. Both estuaries receive different volumes of treated sewage waters. The Mdloti receives 8 ML.d-1, while the Mhlanga receives 20 ML.d-1, resulting in a capping flow of 0.092 and 0.23 m3.s-1, respectively. Through these effluents, eutrophication is enhanced and periods of mouth opening are also increased and prolonged, particularly at the Mhlanga. The aim of this study was to investigate fluctuations in MPB biomass in the Mdloti and the Mhlanga systems, with emphasis on freshwater flow and the alternation of closed and open phases. Sediment samples for MPB biomass were collected on a monthly basis, between March 2002 and March 2003, in the lower (mouth), middle, and upper (head) reaches of the two estuaries. MPB biomass ranged from 1.33 to 391 mg chI a m-2 and from 1.7 to 313 mg chI a m-2 in the Mdloti and the Mhlanga, respectively. A I-way ANOVA revealed no significant differences in MPB chI a concentrations between the two estuaries for the entire data set (Fl, 76 =1.48, P > 0.05). At the Mdloti, MPB biomass varied considerably, with values ranging from 1.33 to 131 mg chI a m-2 during the open phase, and from 18 to 391 mg chI a m-2 during the closed phase. A Mann-Whitney U test confirmed the high significance of these differences between open and closed phases (U= 29, P < 0.001). At the Mhlanga, MPB biomass ranged from 7.0 to 313 mg chI a m-2 during the open phase, and from 1.7 to 267 mg chI a m-2 during the closed phase. Unlike what was observed at the Mdloti, the higher MPB values at the Mhlanga were not always associated with the closed mouth state. In relation to key physico-chemical and biological factors, grazing pressure exerted by the zooplankton community appeared to have played a major role in controlling MPB biomass. Zooplankton biomass was consistently and positively correlated to MPB biomass throughout the study period both at the Mdloti (r = 0040, P < 0.001) and at the Mhlanga (r = 0.33, p < 0.05). Unlike what was shown in previous studies, light attenuation was not significantly correlated with MPB biomass during the period ofthe study, either at the Mdloti or the Mhlanga. These results show that the opening and closing of the mouth play a key role on the MPB biomass of both estuaries. The Mdloti seems to function as a typical TOCE, with prolonged open and closed phases. The Mhlanga, on the other hand, lacks a prolonged closed phase. This, in turn, affects its entire trophic structure and functioning.Thesis (M.Sc.)-University of KwaZulu- Natal, 2004.
50
Lee, SH. "The photosynthetic response and extracellular carbohydrate production of tropical and temperate microphytobenthos." Thesis, 2019. https://eprints.utas.edu.au/31419/1/Lee_whole_thesis.pdf.
Full textAbstract:
Microphytobenthos (MPB) is a community of unicellular microorganisms that inhabit the photic zone of intertidal and subtidal areas of benthic zones. MPB contributes up to half of the total coastal primary productivity, as well as providing a major food source for many invertebrates, small fish and wading birds. Additionally, MPB plays an important role in stabilising the sediment by producing extracellular carbohydrates that form biofilms, which bind sediment particles together.
Intertidal zones experience extreme spatial and temporal fluctuations in both their physical, i.e. temperature, irradiances, and tidal position, and chemical, i.e. salinity and nutrient, conditions. MPB, therefore, needs to employ a variety of mechanisms to cope with these changes; these include behavioural changes, such as positioning themselves at the optimum position within the sediment, and physiological changes to their photosynthetic machinery. Extracellular polymeric substances (EPS) are one of the major components of the extracellular carbohydrates produced by MPB when they are undertaking these mechanisms. Much of this extracellular carbohydrate is produced for vertical migration but some is also produced as a product of photosynthetic overflow, when the MPB is experiencing photoinhibition.
This study focuses on the photosynthetic performance of MPB in different regions. As extracellular carbohydrate production and photosynthesis are often correlated, this relationship is examined in more detail here. A Pulse Amplitude Modulated (PAM) Fluorometer was used to measure the photosynthetic performance of the MPB, while several different approaches were used to investigate the extracellular carbohydrate production.
MPB species composition varies between regions and so the response mechanisms would also be expected to differ. The second chapter of this study focused on the investigation of the relationship between photosynthesis and extracellular carbohydrate production in a southern temperate region of greater Hobart area, Tasmania, at Penna Beach and Kings Beach, of different sediment grain size composition. The MPB was found to be well-adapted to its changing environment and did not experience photoinhibition during environment extremes, although its photosynthetic performance to change to cope with its changing environment. The performance varied between sampling sites and significant differences were found between biomass, photosynthetic performance, and extracellular carbohydrate production. Penna Beach was found to have significantly higher chlorophyll α (chl.α), extracellular carbohydrate concentrations and photosynthetic performance than Kings Beach. The analysed parameters also varied significantly seasonally, with both chl.α and extracellular carbohydrate concentrations higher during spring and summer, while photosynthesis was higher during winter. Monosaccharides concentrations were found to be higher than polysaccharide concentrations at both sampling sites. However, there was no seasonal variations in mono- and polysaccharide concentrations.
The photosynthetic performance and carbohydrate production of MPB in a tropical region, Penang, Malaysia, was examined in Chapter 3. The chl.α and extracellular carbohydrate concentrations varied between sampling sites, where they were mainly affected by sediment temperature, salinity, and irradiance. Nitrate was the only nutrient that had a significant impact on the chl.α concentration and none of the major nutrient had a significant effects on the total carbohydrates (TCHO), monosaccharides (MCHO), or polysaccharides (PCHO). PCHO concentrations were significantly higher than TCHO at all sampling sites. Measured variable fluorescence showed that the MPB were not experiencing optimal conditions at any site, consistently having low photosynthetic efficiency (F\(_v\)/F\(_m\)). Unlike chl.α and extracellular carbohydrate, the photosynthetic performance was not affected by sediment temperature, salinity or irradiance. Photosynthesis was mostly affected by nutrient levels.
The colloidal monosaccharide component of carbohydrate was not able to be measured by the techniques used in earlier chapters (Chapters 2 and 3). In Chapter 4, however, using HPLC, the composition of the monosaccharide component was further differentiated into the key sugars, i.e. glucose, galactose, mannose, arabinose, rhamnose, and xylose. Glucose, which can be produced as photosynthetic overflow at high irradiances and low nutrients, was the major sugar in all samples at both sites. Furthermore, the glucose production varied significantly between sampling sites, with glucose concentrations at Penna Beach much higher (>0.1 mg/mL) than those of Kings Beach (<0.05 mg/mL). Glucose concentrations also varied significantly between seasons, being highest during spring and lowest during winter at Penna Beach, but this was not observed at Kings Beach. Additionally, the chl.α normalised glucose concentration did not vary between sampling depths at either site.
Real-time production of glucose was determined in the fifth chapter of this study, using an innovative experimental approach that adopted glucose biosensors to measure real-time changes in the concentration. Results showed that in natural communities, glucose production increased under high light and nutrient deficient conditions, although the single species cultures had a more variable response. In a bacterial consumption experiment, glucose was rapidly consumed by bacteria in the dark. However, when the culture was treated with an antibiotic, consumption in the dark was minimal.
This study showed that MPB are able to rapidly adapt to changes in their environment. Extracellular carbohydrate, particularly glucose, was excreted mainly as a photosynthetic overflow product. Additionally, glucose biosensors have proven to be a reliable and innovative tool to measure the targeted sugar exudation in microphytobenthic biofilms and have considerable potential in future studies of MPB.