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1
Madikiza, Liwalam Onwabile. "The role of grazers and basal sustrate cover in the control of intertidal algal distribution". Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&.
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2
Graham, Sylvia Lynne. "Growth and grazing of microzooplankton in response to the harmful alga Heterosigma akashiwo in prey mixtures /". Online version, 2008. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=305&CISOBOX=1&REC=8.
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3
VENULEO, MARIANNA. "Algal responses to abiotic and biotic environmental changes". Doctoral thesis, Università Politecnica delle Marche, 2017. http://hdl.handle.net/11566/245503.
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L’eterogeneità delle risposte fisiologiche delle microalghe ai cambiamenti ambientali rappresenta uno dei fattori più importanti nel determinare le interazioni tra le specie in ambiente. La mia ricerca ha rivelato che specie differenti sono diversamente inclini a modificare la propria composizione cellulare in risposta ai cambiamenti ambientali. La scelta tra acclimatazione e omeostasi dipende anche dal tipo e dalla durata della perturbazione in esame. La maggior parte delle alghe considerate nel mio studio, per esempio, ha mostrato una risposta omeostatica ai cambiamenti nelle concentrazioni ambientali di CO2 e nella forma di azoto disponibile. Non è stato ritrovato nessun legame tra la strategia di risposta e la tassonomia delle alghe.
Particolare attenzione è stata rivolta a Chromera velia, parente prossima dei parassiti Apicomplexa e probabile simbionte di coralli dell’ordine Scleractinia. C. velia si è dimostrata perfettamente in grado di vivere ad alta CO2. Questa condizione ha stimolato la produzione di C organico da parte di C. velia, incrementato la sua efficienza di utilizzo dei nutrienti e ha determinato cambiamenti nei rapporti stechiometrici tra gli elementi. Si può ipotizzare, dunque, che l’elevata concentrazione di CO2 rinvenuta all’interno dei tessuti del corallo che circondano il simbionte possa facilitare la vita di quest’alga in simbiosi.
Infine, ho potuto dimostrare che le interazioni tra alghe e ambiente possono avere conseguenze nei rapporti tra alghe e loro predatori. I miei esperimenti hanno mostrato che i copepodi (ma non i rotiferi) possono discriminare tra alghe che sono identiche in ogni aspetto tranne che nella composizione cellulare. La storia nutrizionale delle alghe, dunque, essendo uno dei principali determinanti della loro composizione cellulare, risulta un elemento di grande importanza nelle relazioni tra alghe e predatori.Algae exhibit a large variety of physiological responses to the environmental changes. Such heterogeneity of responses, which is a major determinant of species interaction in natural algal assemblages, was the target of my research. My results show that different species are differently prone to change their cell composition in response to environmental changes, depending on the type and duration of the perturbation. When algae are exposed to changes in the N source and in the CO2 availability, for instance, homeostasis appears as a much more common strategy than usually believed. No link between the response modes and the taxonomy of the examined species was found. I paid special attention to Chromera velia, a photosynthetic relative of apicomplexan parasites that is likely involved in symbiotic associations with scleractinian corals. This alga seems perfectly capable of copying with very high CO2. Life at high CO2 stimulates the overall organic C production of C. velia, increases its nutrient use efficiency and changes the stoichiometric relationships among elements within the cell. The high CO2 concentrations that has been reported in the animal tissue surrounding the photosynthetic cells may therefore facilitate C. velia life in symbiosis. Finally, I have demonstrated that the interactions between algae and environment can affect the relationships between algae and their grazers. My experiments show that the copepods are able to discriminate among algae identical in all aspects but in cell composition, while the rotifers are not. Therefore, the nutritional history of algae, which has the potential to affect algal cell composition, appears as a major determinant of the relationships between algae and grazers.
4
Vost, L. M. "The influence of grazing by the sea urchin Echinus esculentus L. on subtidal algal communities". Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372713.
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5
Rosser, S. M. Jane Horner. "Phytoplankton ecology in the upper Swan River estuary, Western Australia: with special reference to nitrogen uptake and microheterotroph grazing". Thesis, Curtin University, 2004. http://hdl.handle.net/20.500.11937/1562.
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Phytoplankton succession and abundance in estuaries is known to be influenced by the relative strengths of various seasonally changing physical and chemical factors. Previous studies of Swan River Estuary phytoplankton biomass and composition have identified salinity, temperature, rainfall and nutrients as the most important controlling factors. These conclusions are generally based on analysis of data from river length transects and depth integrated day-time sampling. They describe influences ,affecting whole system phytoplankton abundance and succession. Many of the typical seasonal bloom that develop are ephemeral and only extend over relatively small areas. The focus of this study is a single site, Ron Courtney Island, considered typical of the upper estuary region. This region of the estuary was chosen as representative of the section of river most influenced by allochthonous nutrient input. It has been the region of most frequent and intense algal blooms over the past decade. The factors, physical, biological or physiological, that have the greatest influence on controlling phytoplankton biomass under various ambient conditions for this system are determined. While previous studies have recognised the importance of nitrogen to phytoplankton growth in the Swan River Estuary, they have focused on NO;, with only anecdotal reference to the importance of the alternative nitrogen source, NH4+. This is the first study to explore the influence of different nitrogen source fluxes on phytoplankton biomass in the upper Swan River Estuary. The roles of physiological adaptation to, and preferences for, 'new' (NO,), recycled (NH4+) and organic (urea) nitrogen sources in relation to ambient nutrient levels are explored.Specific uptake rates (v), normalised to chlorophyll a, for NO;, NH4+ and urea were 0.2 ± 0.04 - 1831.1 ± 779.19, 0.5 ± 0.26 - 1731.6 ± 346.67 and 3.0 ± 0.60 - 2241.2 ± 252.56 ng N μg Chla-1 respectively. Urea concentration (14.8 - 117.7 μg urea-N 1-1) remained relatively constant over the 12 month study period. Measured ambient specific uptake rates for urea represent between 27.5% and 40.4% of total N uptake over the annual period February 1998 -January 1999. Seasonal nitrate uptake over the same period constituted only 11.3% (±10.77%, n=12) to 24.4% (± 13.02%, n=12) with the highest percentage during winter, when nitrate levels are elevated. It is suggested that urea provides a nutrient intermediary over the spring - summer period during transition from autotrophic to heterotrophic dominated communities. Grazing ,and nitrogen recycling are intricately connected by simultaneously providing top-down biomass control and bottom-up nutrient supply. Zooplankton (> 44 μm) grazing has been shown to reduce up to 40% of phytoplankton standing stock at times. Microheterotrophs (<300 pm) can reduce phytoplankton biomass production by up to 100% (potential production grazed, 11.1% day' - 99.6 % day-1) over an annual cycle. This correlated to mean seasonal day-time grazing loss of 80.47 ± 3.5 ngN μg Chla-1 in surface waters and 20.17 ± 9.7 ngN μg Chla-1 at depth (4.5m). Night time grazing for surface and bottom depths resulted in similar nitrogen loss rates (13.03 ± 4.84 ngN μg Chla-1).Uptake rates for nitrate (r2 0.501) and urea (r2 0.512), doing with temperature (r2 0.605) were shown to have the greatest influence on phytoplankton distribution over depth and time. This research emphasises the need for more detailed investigations into the physiology of nutrient uptake and the effects of nutrient fluxes on phytoplankton biomass and distribution. Further research into the roles of organic nitrogen and pico and nanoplankton in this system is recommended.
6
Kennedy, Matthew R. "The Role of Microzooplankton and Mesozooplankton Grazing During the Planktothrix-Dominated Cyanobacterial Blooms in Sandusky Bay, Lake Erie". Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1589546747826657.
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7
Rosser, S. M. Jane Horner. "Phytoplankton ecology in the upper Swan River estuary, Western Australia: with special reference to nitrogen uptake and microheterotroph grazing". Curtin University of Technology, Department of Environmental Biology, 2004. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16266.
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Phytoplankton succession and abundance in estuaries is known to be influenced by the relative strengths of various seasonally changing physical and chemical factors. Previous studies of Swan River Estuary phytoplankton biomass and composition have identified salinity, temperature, rainfall and nutrients as the most important controlling factors. These conclusions are generally based on analysis of data from river length transects and depth integrated day-time sampling. They describe influences ,affecting whole system phytoplankton abundance and succession. Many of the typical seasonal bloom that develop are ephemeral and only extend over relatively small areas. The focus of this study is a single site, Ron Courtney Island, considered typical of the upper estuary region. This region of the estuary was chosen as representative of the section of river most influenced by allochthonous nutrient input. It has been the region of most frequent and intense algal blooms over the past decade. The factors, physical, biological or physiological, that have the greatest influence on controlling phytoplankton biomass under various ambient conditions for this system are determined. While previous studies have recognised the importance of nitrogen to phytoplankton growth in the Swan River Estuary, they have focused on NO;, with only anecdotal reference to the importance of the alternative nitrogen source, NH4+. This is the first study to explore the influence of different nitrogen source fluxes on phytoplankton biomass in the upper Swan River Estuary. The roles of physiological adaptation to, and preferences for, 'new' (NO,), recycled (NH4+) and organic (urea) nitrogen sources in relation to ambient nutrient levels are explored.Specific uptake rates (v), normalised to chlorophyll a, for NO;, NH4+ and urea were 0.2 ± 0.04 - 1831.1 ± 779.19, 0.5 ± 0.26 - 1731.6 ± 346.67 and 3.0 ± 0.60 - 2241.2 ± 252.56 ng N μg Chla-1 respectively. Urea concentration (14.8 - 117.7 μg urea-N 1-1) remained relatively constant over the 12 month study period. Measured ambient specific uptake rates for urea represent between 27.5% and 40.4% of total N uptake over the annual period February 1998 -January 1999. Seasonal nitrate uptake over the same period constituted only 11.3% (±10.77%, n=12) to 24.4% (± 13.02%, n=12) with the highest percentage during winter, when nitrate levels are elevated. It is suggested that urea provides a nutrient intermediary over the spring - summer period during transition from autotrophic to heterotrophic dominated communities. Grazing ,and nitrogen recycling are intricately connected by simultaneously providing top-down biomass control and bottom-up nutrient supply. Zooplankton (> 44 μm) grazing has been shown to reduce up to 40% of phytoplankton standing stock at times. Microheterotrophs (<300 pm) can reduce phytoplankton biomass production by up to 100% (potential production grazed, 11.1% day' - 99.6 % day-1) over an annual cycle. This correlated to mean seasonal day-time grazing loss of 80.47 ± 3.5 ngN μg Chla-1 in surface waters and 20.17 ± 9.7 ngN μg Chla-1 at depth (4.5m). Night time grazing for surface and bottom depths resulted in similar nitrogen loss rates (13.03 ± 4.84 ngN μg Chla-1).
Uptake rates for nitrate (r2 0.501) and urea (r2 0.512), doing with temperature (r2 0.605) were shown to have the greatest influence on phytoplankton distribution over depth and time. This research emphasises the need for more detailed investigations into the physiology of nutrient uptake and the effects of nutrient fluxes on phytoplankton biomass and distribution. Further research into the roles of organic nitrogen and pico and nanoplankton in this system is recommended.
8
Manley, Nicola Louise. "Polyphenolic compounds in intertidal fuciod algae and their effectiveness as grazing deterrents". Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333575.
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Rowcliffe, J. Marcus. "The population ecology of brent geese and their food plants". Thesis, University of East Anglia, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365866.
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10
Schwinnen, Chad Robert. "Impacts of a Herbivorous Fish, Campostoma anomalum (central stoneroller), on Nitrogen Fixation by Benthic Algae". Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1284993489.
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11
Steele, Nikita. "Geographical variation in effects of nutrient levels and grazing intensity on community structure between upwelling and non-upwelling regions of South Africa". Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013013.
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The aim of this thesis was to assess the influence of upwelling on alga-grazer interactions in rocky shore communities along the south coast of South Africa using grazer exclusion treatments with controls and procedural controls set out in a block design and monitored for algal cover roughly monthly for one year. In the first experiment grazers were excluded from treatment plots at two upwelling and two non-upwelling sites and the rates of algal biomass accumulation were then compared. The upwelling sites showed significantly faster algal colonisation rates, with Ulva rigida being the first species to colonise the rocks. Final algal cover and biomass did not differ significantly between upwelling and non-upwelling sites in control plots open to grazers, but were significantly higher in grazer exclusion plots at upwelling sites indicating stronger grazing effects. This was confirmed by estimating the intensity of grazing using the log-response ratio (LRR), which was calculated from treatment and control plots. Upwelling sites had significantly lower LLR values indicating stronger grazing effects, than at non-upwelling sites, despite no difference in grazer abundances. The second experiment examined the effects of nutrient addition on algal growth and community composition by comparing high nutrient enrichment plots with low enrichment plots at one upwelling and one non-upwelling site. ANOVA indicated faster growth rates and significantly higher final algal biomass in high enrichment plots compared to low enrichment and control plots at both upwelling and non-upwelling sites. A two-way ANOVA indicated significantly higher algal cover in high enrichment plots compared to the data from the grazer exclusion plots in experiment 1 at both sites, suggesting that nutrient addition plays a major role in algal growth and community composition. The findings of these studies have shown significant differences between treatments, sites and seasons, with significant differences not only occurring in algal cover but also accumulation of algal biomass and recruitment patterns between treatments. The small scale local processes acting within a few centimetres (plots) or tens of meters (among blocks) can also be reflected over larger scales such as sites (upwelling/non-upwelling shores). Further, these studies have demonstrated that various factors such as the effects from increased nutrients at upwelling cells and the change in grazing effects due to enhanced nutrients can determine the abundance and diversity of the community structure, including an increase in the abundance of the fast growing algae Ulva rigida, and a slow recovery of the brown and red algae.
12
Diaz, Diaz Eliecer Rodrigo. "Hierarchical spatial structure and levels of resolution of intertidal grazing and their consequences on predictability and stability at small scales". Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1005393.
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The aim of this research was to assess three hierarchical aspects of alga-grazer interactions in intertidal communities on a small scale: spatial heterogeneity, grazing effects and spatial stability in grazing effects. First, using semivariograms and cross-semivariograms I observed hierarchical spatial patterns in most algal groups and in grazers. However, these patterns varied with the level on the shore and between shores, suggesting that either human exploitation or wave exposure can be a source of variability. Second, grazing effects were studied using manipulative experiments at different levels on the shore. These revealed significant effects of grazing on the low shore and in tidal pools. Additionally, using a transect of grazer exclusions across the shore, I observed unexpected hierarchical patchiness in the strength of grazing, rather than zonation in its effects. This patchiness varied in time due to different biotic and abiotic factors. In a separate experiment, the effect of mesograzers effects were studied in the upper eulittoral zone under four conditions: burnt open rock (BOR), burnt pools (Bpool), non-burnt open rock (NBOR) and non-burnt pools (NBpool). Additionally, I tested spatial stability in the effects of grazing in consecutive years, using the same plots. I observed great spatial variability in the effects of grazing, but this variability was spatially stable in Bpools and NBOR, meaning deterministic and significant grazing effects in consecutive years on the same plots. Both the significance in grazing effects and spatial stability depended on the level of resolution (species, functional, biomass) at which the algal assemblage was evaluated, suggesting hierarchical variability. In order to be able to predict spatial variability in the effects of grazers in the upper eulittoral zone using biotic and abiotic micro- and macrofactors, a conceptual model was proposed, based on data from several multiple-regressions. This linked the interactions among three elements: idiosyncratic heterogeneity, micro and macrofactors. This suggests that spatial variability can be a product of these factors, while spatial stability can be caused by the same or different combinations of factors. In conclusion, grazing and other ecological phenomena must be studied hierarchically, not only through spatiotemporal scales, but also at different levels of resolution, as these also influence our perception of patterns.
13
Zhang, Hongyan. "Ecological modeling of the lower trophic levels of Lake Erie". Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1163785412.
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Piarulli, Stefania. "Divergence patterns in Fucus seaweeds (Phaeophyceae) in the northern Baltic Sea and in the Tjongspollen area". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9544/.
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To be able to interpret patterns of biodiversity it is important to understand the processes by which new species evolve and how closely related species remain reproductively isolated and ecologically differentiated. Divergence and differentiation can vary during speciation and it can be seen in different stages. Groups of closely related taxa constitute important case studies to understand species and new biodiversity formation. However, it is important to assess the divergence among them at different organismal levels and from an integrative perspective. For this purpose, this study used the brown seaweeds genus Fucus as a model to study speciation, as they constitute a good opportunity to study divergence at different stages. We investigated the divergence patterns in Fucus species from two marginal areas (northern Baltic Sea and the Tjongspollen area), based on phenetic, phylogenetic and biological taxonomical criteria that are respectively characterised by algal morphology, allele frequencies of five microsatellite loci and levels of secondary polyphenolic compounds called phlorotannins. The results from this study showed divergence at morphological and genetic levels to certain extent but complete lack of divergence at biochemical level (i.e. constitutive phlorotannin production) in the Baltic Sea or Norway. Morphological divergence was clearly evident in Tjongspollen (Norway) among putative taxa as they were identified in the field and this divergence corresponds with their neutral genetic divergence. In the Baltic, there are some distinguishable patterns in the morphology of the swedish and finnish individuals according to locality to certain extent but not among putative taxa within localities. Likewise, these morphological patterns have genetic correspondence among localities but not within each locality. At the biochemical level, measured by the phlorotannin contents there were neither evidence of divergence in Norway or the Baltic Sea nor any discernable aggregation pattern among or within localities. Our study have contributed with further understanding of the Baltic Sea Fucus system and its intriguingly rapid and recent divergence as well as of the Tjongspollen area systems where formally undescribed individuals have been observed for the first time; in fact they appear largely differentiated and they may well warrant a new species status. In current times, climate change threatens, peripheral ecosystems, biodiversity, and increased knowledge of processes generating and maintaining biodiversity in those ecosystems seem particularly important and needed.
15
Abitha, R. "Algiculture - A Novel Algae Cultivation Technique for Sustinable Algal Biofuel Production and Capture of Green House Gases". Thesis, 2016. http://etd.iisc.ac.in/handle/2005/4070.
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Algal biofuel has been shown to have great potential to solve the World’s sustainable energy crisis but technologies for large-scale cultivation are still elusive. While photobioreactors meet very high value algal products there is still no technology for producing algae by the millions of tons. Flooded paddy lands of India offer excellent opportunities for co-cultivation of algae with paddy crop provided it meets various sustainability criteria, not to mention very low cost options. This research examines sustainability, technology and climate change challenges to this above concept termed “Algiculture”. The potential of naturally emerging algal consortia to overcome travails of pure-culture, the ability to scavenge ‘lost’ plant nutrients in flooded paddy, overcome threats by grazers and predators, evolving naturally mediated techniques to harvest algae, impact on methane emissions, etc. were examined critically under laboratory and flooded paddy conditions. Experimental results indicate that many of the sustainability criteria can be met by growing algae simultaneously with a paddy crop for the first 60-75d which doubles the overall biomass yield from such lands. Algae raised can scavenge ammoniacal-N that generally occurs as unavoidable losses in flooded paddy system and can thus be raised without additional fertilizer inputs. This simultaneously ameliorates the N-pollution from paddy runoff to water bodies. Algal cultivation with paddy (Algiculture) alters micro-environmental conditions e.g. oxygen supersaturation, to make methane emissions unfavourable and by contrast algae even take up the C hitherto wasted away as methane and thereby converting an environmental liability to conservation. Consortia dominated by Chlorella and Chlorococcum sp. along with a small number of Cyanophycaeans facilitate simple low energy algal harvest techniques employing clumping and floc-formation that enables maintaining appropriate stocking density of algae and allowing continuous operation. The pattern of grazer /predator occurrence in such systems, techniques to minimize their influence by merely altering the cultivation conditions have been worked out and tested successful. The causes of reduction in methane emissions and C-source identification have
been assessed with 13C discrimination studies. The research creates a new potential reducing GHG on the one hand for also raising sustainable bioenergy options in India as well as in all flooded paddy lands of the world
16
Campbell, Jena Renee. "The role of protozoan grazers in harmful algal bloom dynamics : tools for community and grazing analyses". 2012. http://hdl.handle.net/2152/19574.
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Harmful algal blooms (HABs) are becoming more prevalent throughout the world’s aquatic systems. These blooms have been the subjects of numerous studies because they can cause human health issues and economic impact through fish kills, contaminated shellfish and decreased tourism. Much research has focused on the “bottom-up” aspect of these blooms; namely, the potential role of increased nutrient input into coastal waters from anthropogenic sources causing increased growth in harmful algal species. However, there are also potential “top-down” controls affecting the rate at which harmful algal species are consumed by grazers. The aim of this project was to determine protozoan grazer population fluctuations and their grazing impact on HAB species through field monitoring and laboratory grazing experiments. Protozoan grazers were chosen because their growth rates could potentially keep up with those of HAB species. Declines in grazer populations before the onset of a bloom could be indicative of a release of the HAB from a “top-down” grazing control. Field samples taken during bloom and non-bloom events helped elucidate any microplankton community changes. After establishing that there appear to be changes to the grazer population before and after a bloom, ingestion experiments including direct epifluorescence microscopy and DNA analyses were conducted to determine if it is possible that a chosen protozoan grazer can ingest a HAB species. Finally, experiments were conducted to determine whether the HAB species was a favorable food source for the grazer. Population growth experiments in which grazers are fed a HAB species, 50:50 mixture, or normal culture food source were used to determine the survival and growth rate of the grazer. Although certain ciliates and heterotrophic dinoflagellates were found to feed on HAB species in the lab and in natural bloom samples, the HAB species as a food source produces lower grazer growth rates than on control food. Protozoan grazers may be a more effective control during bloom initiation than after the bloom has been established.text
17
Wang, Hung-Yu, i 汪鴻玉. "Effects of environmental factors, disturbance, and grazing of fish on the succession of algal communities in Hapen Creek". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/36410373671903210222.
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碩士國立臺灣大學
動物學研究所
91
A study on the interaction between environmental factors and algal communities in Hapen Creek was conducted from March 2002 to March 2003. Six study sites, including lotic and lentic habitats, were chosen. A total of 38 diatom species, 11 of cyanobacteria, and 7 of green algae were identified from these sites. The results of PCA ordination showed that higher correlation coefficients were obtained between the algal communities and those variables such as current velocity, depth, DO, conductivity, and nitrate, suggesting that these variables should have played more important roles than others in determining the structure of the algal communities and the growth of algae in riffles, although pH, turbidity, and orthophosphate were found to have effects on algae in pools. Under undisturbed condition, both of the algal biomass (in terms of chlorophyll a and AFDM) and Shannon species diversity index in lotic habitats were higher than those in lentic habitats. Under disturbed condition, in contrast, there were decreases in the algal biomass and diversity in either habitat, and, as a result, certain changes in community structure. It was found that habit disturbance caused significantly a lowering in the abundance of diatoms, but an enhancement in that of green algae in the riffles as well as cyanobacteria in the pools. This study showed that when algal communities were confronted by frequent disturbance, those of long-lived and more resistant species, such as Cocconeis placentula and Gongrosira sp., would dominate over others and replaced consequently the early invader such as Oedogonium sp. Taiwan shoveljaw carp (Varicorhinus barbatulus), feeding on attached algae, is the most dominant fish in Hapen Creek. The study of the grazing effects of V. barbatulus on algal communities in both of the lotic and lentic habitats in Hapen Creek was done from December 2002 to March 2003. The collected algal assemblages from grazed treatment (viz., grazed by V. barbatulus) would be analyzed with those from undisturbed, disturbed, and exposed treatments (viz., boulders exposed to grazers in streams) to examine the short-term biotic interactions. The results showed that the grazing of V. barbatulus not only reduced the biomass of the algae, but also altered the structure and composition of algal assemblages. The grazing effect of V. barbatulus has given rise to a decrease in the relative abundance of diatoms and an increase in greens in lotic habitats or blue-greens in lentic habitat as well. The composition of algal assemblages of grazed treatment was similar with that of exposed treatments. Hence, it was found that V. barbatulus exerted a density-dependent consumption effect on the attached algae and might thus be considered a keystone herbivore in the study area.
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Burt, Alexis Emelia. "Mercury uptake and dynamics in sea ice algae, phytoplankton and grazing copepods from a Beaufort Sea Arctic marine food web". 2012. http://hdl.handle.net/1993/8907.
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Mercury (Hg) is one of the primary contaminants of concern in the Arctic marine ecosystem. Methyl Hg (MeHg) is known to biomagnify in food webs. During the International Polar Year - Circumpolar Flaw Lead study, sea ice, seawater, bottom ice algae, phytoplankton and the herbivorous copepods were collected from the Amundsen Gulf to test whether ice algae and phytoplankton assimilate Hg from their habitat, and whether Hg bioaccumulates from the seawater to the primary consumers. Sea ice algae were found to accumulate Hg primarily from the bulk bottom ice, and the sea ice algae bloom depleted Hg stored within the bottom section of the ice. Furthermore, biodilution of Hg was observed to occur in sea ice algae. Higher concentrations of Hg were also found in phytoplankton and in grazing copepods. A positive correlation between MeHg and trophic level suggests the occurrence of MeHg biomagnification even at these low trophic positions.
19
Diaz, Diaz Eliecer Rodrigo. "Hierarchical spatial structure and levels of resolution of intertidal grazing and their consequences on predictability and stability at small scales /". 2008. http://eprints.ru.ac.za/1558/.
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Kaehler, S., i Pierre William Froneman. "Temporal variability in the effects of grazing by the territorial limpet Patella longicosta on the productivity of the crustose alga Ralfsia verrucosa". 1999. http://hdl.handle.net/10962/d1011956.
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This study reports the effects of grazing by the territorial limpet Patella longicosta on the productivity of the encrusting alga Ralfsia verrucosa. Grazing significantly increased algal growth during the first month of the study (August). Simulated grazing by brushing also enhanced productivity. However, the productivity of grazed and ungrazed algae did not differ significantly during the ensuing three months. As the growth of ungrazed plants remained the same throughout the study, the elevated productivity of grazed plants during August was attributed to increased limpet activity. The variation in grazer-induced algal growth was possibly associated with increased feeding when the limpets embark on energetically costly periods of reproduction.