Dissertationen zum Thema „Intertidal gastropods“

Phenotypic plasticity, the differential phenotypic expression of the same genotype in response to different environmental conditions, is a paradigm central of the study of evolution and ecology and is at the core of the "nature versus nurture" debate. Here, the marine gastropod Littorina littorea was used as a model to further our understanding of the potential role of phenotypic plasticity in intertidal systems. In the first study L. littorea was included in an investigation of induced defences across six species of intertidal marine gastropods in the families Littorinidae and Trochidae. Species differed in the magnitude and type of plastic response, which appeared to relate to their susceptibility to crab predation. Chapters three and four revealed that L. littorea was able to alter its degree of morphological plasticity depending on temporal variation in predation threat. Snails exposed to predation threat halfway through trials appeared to "catch up" snails continuously exposed to predator cues in, terms of their shell size, whereas snails experiencing a removal of predation cues showed a significant reduction in growth rate following this switch in predation environment. A further investigation suggested that Littorina littorea demonstrated no significant difference in the morphological traits under variable predator threat versus a constant predator' threat environment. Finally, the interaction between biotic (predator) and abiotic (temperature) environmental effects revealed that snails maintained at 16 and 20° C demonstrated significant induced defences by growing larger and thicker shells, but there was no significant difference in induced defences between these two temperatures. However, the expression of induced defences was much lower at 24° C with only negative significant response in two of shell traits IV between control and predator cue treatments which may indicate that induced defences was inhibited at this temperature treatment. The implications of these results are discussed as is the potential applications of induced defences.

Les organismes intertidaux vivent dans un environnement variable et complexe et sont soumis à de nombreux stimulus et stress. Récemment, de nouvelles études sur les capacités sensorielles de ces gastéropodes et sur leur capacité à se déplacer dans leur environnement, ont démontrées que leur répertoire comportemental était plus large que prévu. Dans ce contexte, cette thèse a pour but d’améliorer nos connaissances sur le comportement de thigmotaxie chez Littorina littorea. La thigmotaxie a donc été testée dans des dispositifs expérimentaux de différentes tailles et de différentes formes. Cette approche permet aux individus de rencontrer des discontinuités en 2-dimension ou en 3-dimension et a pour but d’aider à comprendre comment la complexité topographique de leur environnement peut modifier le comportement thigmotactique chez les gastéropodes. La thigmotaxie a aussi été testée sous différentes conditions de salinité pour comprendre comment ces variations de salinité peuvent altérer leur comportement. En effet, les organismes intertidaux sont soumis à de larges variations de salinité pendant les périodes d’émersion. Pendant ces périodes d’émersion, ils sont aussi soumis à de grandes variations de température (jusqu’à 20°C). Ce travail s’intéresse aussi au comportement thermique des gastéropodes intertidaux via l’étude de la température du corps de L. littorea et de Patella vulgata et celle de leur microhabitat. Ces températures sont étudiées durant 4 jours ensoleillés, de Juin à Décembre, afin de tester le choix d’un microhabitat par ces 2 espèces de gastéropodes sous des conditions de températures auxquelles ils peuvent être soumis au cours d’un cycle saisonnier sur la Côte d’Opale. Le comportement d’agrégation chez L. littorea et les bénéfices thermiques associés précédemment étudiés dans la littérature sont aussi examinés, (i) in situ sous des conditions de vague de chaleur modérée et (ii) ex situ sous des conditions extrêmes de vague de chaleur simulée au laboratoire. En particulier, la température du corps des individus à l’intérieur et de ceux à l’extérieur des agrégats est étudiée pour comprendre l’importance de la position des individus au sein des agrégats.Ces résultats suggèrent que la thigmotaxie semble être l’une des taxies majeures impliquée dans l’orientation des gastéropodes. En effet, même sous des conditions défavorables (i.e. salinité basse), le comportement thigmotactique est observé chez L. littorea. Ce travail souligne également une préférence pour les macrohabitats biogéniques chez L. littorea et P. vulgata, qui permettent de réduire les stress thermique et de dessiccation. Au sein d’un macrohabitat, les organismes intertidaux sont capables de tirer avantage de la mosaïque thermique rencontrée dans leurs environnements et de sélectionner un microhabitat. Chez les gastéropodes, cette sélection de microhabitat est espèce-, température- et habitat-dépendante et leur permet de se maintenir dans leur optimum de températures. Pour finir, ce travail souligne l’absence de bénéfice thermique à être agrégé chez L. littorea sous des conditions de stress thermique. En particulier, sous des conditions de vague de chaleur extrême, la température du corps des individus à l’intérieur de l’agrégat est supérieure à celle des individus à l’extérieur de l’agrégat. Ce résultat pose la question, encore irrésolue, des mécanismes qui entrainent le comportement d’agrégation chez L. littorea.Ces résultats contribuent néanmoins à la preuve croissante qu’étudier le comportement chez les gastéropodes intertidaux est crucial pour comprendre comment ils se déplacent, perçoivent leur environnement et peuvent réagir à l’augmentation des températures dans le cadre du réchauffement global. Ce travail souligne également l’importance d’une meilleure compréhension de la thermorégulation chez les organismes intertidaux, pour permettre une meilleure estimation de l’impact du réchauffement global sur leur écologie
Intertidal organisms inhabit highly variable and complex environments and are submitted to a large range of stimuli and stresses. Recently, new insights into the sensory abilities of intertidal gastropods and their subsequent ability to navigate through topographically complex landscapes demonstrated that the behavioural repertoire of intertidal gastropods is much wider than previously thought. In this context, the present thesis first aimed to ameliorate our knowledge in the thigmotactic behaviour of Littorina littorea. Specifically, thigmotactic behaviour was tested in experimental containers of different sizes and shapes. This approach allowed individuals to encounter two-dimensional and three-dimensional discontinuities in order to understand how the topographical complexity of their environment can modify this behaviour. Thigmotaxis was further tested under decreasing salinity concentrations to understand how salinity can modify gastropods behaviour, since they are typically submitted to large salinity variations during emersion periods. During emersion, intertidal organisms are also submitted to large temperature variations (up to 20°C). Thus, this work also investigated the thermal behaviour of intertidal gastropods by studying body temperature of L. littorea and Patella vulgata and their microhabitat temperature on a rocky platform on the French coasts of the eastern English Channel. Temperatures were investigated on four sunny days from June to December to test the microhabitat choice of these two intertidal gastropods species under temperature conditions typically experienced through a seasonal cycle on the Opal Coast. Aggregation behaviour in L. littorea and the associated thermal benefits previously found in gastropods literature were also investigated, (i) in situ under a moderate heat wave and (ii) ex situ under an extreme heat wave simulated under laboratory-controlled conditions. Specifically, the body temperature of individuals inside and at the edge of aggregates were investigated to assess the importance of the position within aggregates.Taken together, the results of this thesis suggest that the thigmotactic behaviour can be one of the major taxes involved in intertidal gastropods orientation. Indeed, even under unfavourable conditions (e.g. low salinity conditions), the thigmotactic behaviour is still observed in L. littorea. This work also highlighted macrohabitat preference in L. littorea and P. vulgata for biogenic structures which allow to reduce both desiccation and thermal stresses. Within a macrohabitat, intertidal organisms are able to take advantage of the thermal mosaic encountered in intertidal environment and select microhabitat. This microhabitat selection in gastropods, is species- temperature- and habitat-dependent and allows individuals to maintain their body into their optimal range of temperatures. Finally, this work stressed the absence of thermal benefits of being aggregated in L. littorea under heat stress conditions. Specifically, under extreme heat wave, body temperature of individuals inside the aggregate is higher than for individuals at the edge of the aggregate. This result raised the rather unexpected and still unresolved question to understand the mechanisms driving aggregation behaviour in L. littorea. These results nevertheless contribute to the growing evidence that studying behaviour in intertidal gastropods is critical to understand how they move, how they perceive their environment and how they cope with raising temperature under global warming. This work also highlighted the importance of a better understanding of the thermoregulatory behaviour in intertidal organisms, for a better estimation of the impact of global warming in their ecology

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Historical vicariant processes due to glaciations, resulting from the large-scale environmental changes during the Pleistocene (0.012-2.6 million years ago, Mya), have had significant impacts on the geographic distribution of species, especially also in marine systems. The motivation for this study was to provide novel information that would enhance ongoing efforts to understand the patterns of biodiversity on the South African coast and to infer the abiotic processes that played a role in shaping the evolution of taxa confined to this region. The principal objective of this study was to explore the effect of Pleistocene climate changes on South Africa′s marine biodiversity using five intertidal gastropods (comprising four rocky shore species Turbo sarmaticus, Oxystele sinensis, Oxystele tigrina, Oxystele variegata, and one sandy shore species Bullia rhodostoma) as indicator species. Sequence data obtained from partial segments of the mitochondrial cytochrome oxidase c subunit 1 (COI), and the nuclear ribosomal DNA (encompassing part of 5.8S, second Internal Transcribed Spacer and part of 28S, hereinafter called ITS2; or comprising part of the first Internal Transcribed Spacer, 5.8S, second Internal Transcribed Spacer and part of 28S, hereinafter called ITS), were used as genetic markers to construct phylogeographic patterns and to investigate demographic histories of the taxa. Population structure was investigated using haplotype network analyses, pairwise ΦST statistics, analysis of molecular variance (AMOVA), isolation by distance analyses, Bayesian analysis of population structure (BAPS) and coalescent analysis of gene flow. Demographic history was analysed through Fu′s Fs tests, mismatch distributions, and Bayesian skyline plots. Demographic analyses suggest that all five intertidal gastropods studied experienced demographic expansions dating to the late Pleistocene. The sandy shore direct developer B. rhodostoma began expansion after the LGM (c. 15 kya) whereas for the four rocky shore broadcast spawners (T. sarmaticus, O. sinensis, O. tigrina, and O. variegata) the onset of expansion coincided with or preceded the LGM (c. 25, 60, 50, 40 kya, respectively). Consistent with recent range expansions and gene flow patterns, the population genetic structure in all species was characterised by shallow or a lack of population differentiation. Oxystele variegata was an exception as it showed a deep disjunction, of late Pleistocene origin, between individuals in the west coast Namaqua Bioregion and those in the south coast Agulhas Bioregion. These results provide strong evidence of the vital role that Pleistocene climatic changes and current regimes played in shaping the nature and distribution of biodiversity on the South African coast. In addition, gene flow in all species, except O. tigrina, was remarkably asymmetrical with the regions around Cape Infanta and Port Elizabeth acting as source populations. Considering the generally weak population genetic structure and gene flow patterns detected for most gastropod species studied here, it is recommended that T. sarmaticus, O. sinensis, O. tigrina and B. rhodostoma be managed as panmictic populations, and that the region encompassing Cape Infanta, and Port Elizabeth should be prioritised for conservation as it appears to harbour source populations. Oxystele variegata was the only species showing distinct population structure and in this instance, species specific conservation efforts should recognize this divergence by treating the two genetic assemblages as distinct management units.
AFRIKAANSE OPSOMMING: Historiese vikariante prosesse kan toegeskryf word aan glasiasie, en het tot gevolg gehad dat grootskaalse veranderinge in die omgewing plaasgevind het tydens die Pleistoseen (,012 - 2.6 miljoen jaar gelede, Mjg). Dit het 'n beduidende impak gehad op die geografiese verspreiding van spesies, veral ook in die mariene stelsels. Die motivering vir hierdie studie was om nuwe data te voorsien wat sal bydrae tot die voortgesette pogings om die patrone van biodiversiteit langs die Suid-Afrikaanse kus te verstaan. Dit sou ook help om die abiotiese prosesse af te lei wat 'n rol gespeel het in die evolusie van taksa wat in hierdie streek voorkom. Die hoofdoel van hierdie studie was om die effek van die Pleistoseen klimaatsveranderinge op Suid-Afrika se mariene biodiversiteit te bepaal deur gebruik te maak van vyf intergety slak spesies as indikatore (vier wat in rotsagtige gebiede voorkom: Turbo sarmaticus, Oxystele sinensis, Oxystele tigrina, Oxystele variegata en 'n sanderige strand spesies: Bullia rhodostoma). Volgorde data verkry vanaf gedeeltelike segmente van die mitochondriale sitochroom oksidase c subeenheid 1 (COI), en die kern ribosomale DNA (bestaande uit 'n deel van 5.8S, tweede interne getranskribeerde spasieërders en 'n deel van 28S), hierna genoem ITS2 is gebruik as genetiese merkers om filogeografiese patrone te dokumenteer en ook om die demografiese geskiedenis van die spesies te ondersoek. Bevolking struktuur is ondersoek deur gebruik te maak van haplotipe netwerk analise, paarsgewyse ΦST statistiek, analise van molekulêre variansie (AMOVA), isolasie deur afstand analise, Bayesiaanse analise van die bevolking struktuur (BAPS) en analise van gene vloei. Demografiese geskiedenis is ontleed deur Fu se Fs toetse, misparing verdelings, en Bayesiaanse luglyn kurwes. Demografiese ontleding dui daarop dat al vyf die intergety slakke wat ondersoek is demografiese uitbreidings ervaar het wat terugdateer tot die einde van die Pleistoseen. Die sanderige strand direkte ontwikkelaar, B. rhodostoma, het die uitbreiding begin na die LGM (c. 15 Kya), terwyl vir die vier rotsagtige kusbewoners wat eiers oor 'n uitgebreide gebiede versprei (T. sarmaticus, O. sinensis, O. tigrina, en O. variegata) het die aanvang van die bevolkings uitbreiding saamgeval met die laaste galsiasie of dit voorafgegaan (c. 25, 60, 50, 40 Kya, onderskeidelik). In ooreenstemming met die onlangse reeks bevolkings uitbreidings, is die bevolking genetiese struktuur in alle spesies gekenmerk deur weinig differensiasie. Oxystele variegata was 'n uitsondering en het 'n ontwrigting van laat Pleistoceen oorsprong getoon tussen individue langs die weskus Namaqua Biostreek en dié in die suid kus Agulhas biostreek. Hierdie resultate voorsien sterk bewyse van die belangrike rol wat die Pleistoseen klimaatsveranderinge gespeel het in die vorming en verspreiding van biodiversiteit langs die Suid-Afrikaanse kus. Daarbenewens, geen vloei in alle spesies, behalwe O. tigrina, was merkwaardig asimmetries. Kaap Infanta en Port Elizabeth verteenwoordig moontlik die bron bevolkings. Met inagneming van die geringe bevolking genetiese struktuur en geenvloei patrone wat waargeneem is vir die meeste slak spesies wat bestudeer is, word dit aanbeveel dat T. sarmaticus, O. sinensis, O. tigrina en B. rhodostoma bestuur word as 'n panmiktiese bevolking, en dat die streek wat Kaap Infanta en Port Elizabeth insluit geprioritiseer moet word vir bewaring. Oxystele variegata was die enigste spesie wat duidelike bevolking struktuur getoon het en in hierdie geval, moet spesie spesifieke bewaringspogings aangewend word.

With increasing human activity and urban development along coastal areas, much research has recently focussed on examining how fragmentation of habitats affect marine fauna in near-shore environments. This study examines relationships between density of populations and patch-size and the effect of edges of habitat on distributions of minute gastropods (microgastropods) living in patches of coralline algae on intertidal shores in south-eastem Australia.

This study concerns the reproductive and larval ecology of the nudibranch Adalaria proxima. Attainment of competence is demonstrated to be cue specific. Embryos metamorphose in response to choline, yet remain precompetent to elevated potassium and the natural cue until after hatching. It is hypothesized that the choline-mediated metamorphic pathway (or choline-sensitive portion of the natural pathway) becomes functionally complete ontogenetically earlier than do larval chemoreceptors. Larvae metamorphose in response to sea water 'conditioned' (CSW) by the bryozoan Electra pilosa. A range of littoral organisms failed to induce metamorphosis and it is suggested that A. proxima displays a high degree of cue specificy. It is reported that CSW-mediated metamorphosis is dose dependent and effected in a disparate manner to that of potassium. No evidence for a bacterial role in metamorphosis was found. These results are intended to facilitate future isolation of the natural cue. Both starved (lecithotrophic) and fed (facultatively planktotrophic) larvae may successfully delay metamorphosis for 28-31d post-hatching (at 10-C). Larval fitness appeared to be unaffected by nutritional status, which is suggested to reflect the transitional evolutionary nature of facultative planktotrophy. The lowered fitness commensurate with an extended pelagic period is hypothesized to confer a lowered dispersal potential. A. proximais semelparous, producing up to eleven spawn before dying. Significant variation in reproductive traits is demonstrated within and between six U.K. populations of A. proxima Intrapopulation decreases in egg size, fecundity and hatching success with spawn laying sequence are suggested to reflect phylogenetic constraints. Interpopulation differences in egg size and fecundity are considered consistent with the predicted limited larval dispersal potential. Population egg size was correlated to larval size but not latitude or fecundity. Possible causative factors of the observed interpopulation variation in reproductive traits are discussed, and most probable causes hypothesized.

xv, 99 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
The trochid gastropod Chlorostoma (Tegula) funebralis is found in rocky intertidal habitats along the west coast of North America from Baja California to Vancouver Island. Size-frequency distributions of populations were analyzed along a latitudinal gradient from northern Oregon to Baja California. Populations in California and southern Oregon were dominated by individuals in the juvenile size classes (0.1g-2g). Along the Oregon coast, populations dominated by juveniles were correlated with coastline topography, with protected areas having large numbers of juveniles and exposed areas dominated by larger size classes. The largest size classes (>9g) were rarely present in southern populations. The seasonality of reproduction was investigated in a southern California population and an Oregon population to determine whether continuous reproduction in southern populations increases recruitment success over the year and decreases inter-annual variation in reproductive success. Constant recruitment may cause populations to have a large number of juveniles, the observed pattern in southern populations. Although individuals capable of reproduction were found year-round in both populations, the southern population experienced multiple spawning events over the year, while the northern population experienced only one such event. Constant recruitment may be a strategy to compensate for shorter life spans and smaller sizes of individuals in southern California. To investigate whether variations in predation rates on large adult C. funebralis affect the size structure of populations, the main predators and predation rates for different populations in Oregon were identified. All observed predation events were by the intertidal seastar Pisaster ochraceus . Predation pressure by P. ochraceus varied significantly with site and between sampling dates but did not remove enough C. funebralis from the adult population to have a significant effect on population size structure. To determine the connectivity between populations and the maximum dispersal potential, the mitochondrial gene COI was sequenced from individuals from nine populations ranging from southern California to northern Oregon. Although haplotype diversity was high, no genetic structure was found between populations. Rather than an indication of high dispersal potential and a panmictic species, the lack of isolation by distance may be a result of range expansion following the last glacial maximum.
Committee in charge: Patrick Phillips, Chairperson, Biology; Alan Shanks, Advisor, Biology; Craig Young, Member, Biology; Richard Emlet, Member, Biology; Jon Erlandson, Member, Anthropology; Gregory Retallack, Outside Member, Geological Sciences

xiii, 141 p. : ill. (some col.)
The small trochid gastropod Lirularia succincta occurs in rocky intertidal habitats along the Pacific coast of North America. Strong escape responses of adult L. succincta were elicited by the predatory seastars Leptasterias hexactis and Pycnopodia helianthoides but not by the nonpredatory seastar Henricia sp. Escape responses to juvenile L. hexactis were not observed in newly-hatched L. succincta. The snails exhibited weak avoidance responses to water-borne chemical stimuli from L. hexactis. The vertical distribution of a population of L. succincta was described, and changes in the size-frequency distribution of the population in the spring and summer were documented. Finally, factors that may affect oviposition in L. succincta were investigated in the laboratory. The snails deposit egg masses year round with a peak in reproductive output in the summer. In the laboratory and in the field, egg masses are preferentially deposited in crevices.
Committee in charge: Dr. Craig M. Young, Chair; Dr. Richard B. Emlet, Member; Dr. Alan L. Shanks, Member

The management of Australian coastal marine biodiversity is geographically delineated by bioregions defined under the Interim Marine and Coastal Regionalisation of Australia system (IMCRA). The location of boundaries between adjacent IMCRA defined bioregions is based on biotic and abiotic surrogates. Intertidal habitats are not well represented in the IMCRA model, so it is not known whether conservation plans based on IMCRA identified bioregions will effectively represent distinct communities for conservation. Here, I used gastropod molluscs as a model fauna because they are a significant component of intertidal assemblages. The model tested was that patterns of biodiversity exhibited by gastropods should align with IMCRA boundaries. Gastropods have been shown to be a reliable surrogate to assess patterns of biodiversity at larger scales. Tests were performed at different spatial scales under three different and complementary approaches, as surrogates can be effective under varying circumstances. At a continental scale, gastropods exhibited patterns of distribution coinciding with previous classic biogeographical models rather than IMCRA defined bioregions. At a scale of 103 km, gastropod assemblages did not coincide with boundaries set by IMCRA. The genetic structure of the microgastropod Eatoniella atropurpurea, a hyper-abundant species, again did not match bioregional boundaries. Thus, the general model that different bioregions support different assemblages was not supported in my study as the variability found at different spatial scales did not correlate with IMCRA defined boundaries The implications of these results are that different methods of conservation management at b large and fine scale are necessary for the design of marine reserves, as the current model (IMCRA) does not represent patterns of biodiversity at finer scale. New conservation tools must incorporate the natural variability in assemblage structure that occurs at finer scales.

Future changes to the pH and temperature of the oceans are predicted to impact the biodiversity of marine ecosystems, particularly those animals that rely on the process of calcification. The marine intertidal gastropod Littorina littorea can be used as a model of intertidal organism for investigating the effects of ocean acidification and high temperature, alone and in combination because its ability to be quickly adapt against environmental stressor. In the first study a single species population of L. littorea was used to test for physiological and biochemical effects underpinning organismal responses to climate change and ocean acidification. Compared with control conditions, snails decreased metabolic rates by 31% in response to elevated pCO2 while by 15% in response to combined pCO2 and temperature. Decreased metabolic rates were associated with metabolic depression, a strategy to match oxygen demand and availability, and an increase in end-product metabolites in the tissue under acidified treatments, indicating an increased reliance on anaerobic metabolism. This study also showed that anthropogenic alteration of CO2 and temperature may also lead to plastic responses, a fundamental mechanism of many marine gastropods to cope environmental variability. At low pH and elevated temperature in isolation or combined showing lower shell growth than individuals kept under control conditions. Percentage change in shell length and thicknesses was also lower under acidified and temperature in isolation or combined than control condition, making shells were more globular and desiccation rates were higher. Further studies to broader latitudinal ranges for six populations of L. littorea showed that shell growth decreased in all six populations under elevated pCO2 compared to control snails particularly those at range edges. Elevated pCO2 also affected to the reduction of shell length and width that causing shell aspect ratio to increase across latitudinal gradients except individuals from Millport, UK. Percentage changes of aperture width and aperture area were also decrease under elevated pCO2 with greater reduction of aperture area were found at populations in the mid-ranges which is assumed this response might be linked to local adaptation of the individual to microclimatic conditions. This study also showed that metabolic rates were negatively affected by high pCO2 and show non-linear trend across latitudinal gradients in compared to individual kept under normal pCO2 conditions. Metabolomic analysis showed that two northern populations of Trondheim and TromsØ were distinct from other populations when exposed to low temperature (15 °C) with elevated pCO2 due to, in part, high concentrations of thymine, uracil, valine and lysine. A similar separation also occurred under medium (25 °C) and high (35 °C) temperature exposure in which one of northern population (Trondheim) was distinct from other populations and had lower concentrations of alanine, betaine and taurine while higher of valine. These results suggest that populations at northern latitudes may apply different ionic transport mechanisms under elevated pCO2 and elevated temperatures and those populations are likely to vary in terms of their physiological responses to this environmental challenge.

Univ., Diss. u.d.T.: Kim, Dohong: Seasonal dynamics of an Antarctic rocky intertidal, with emphasis on the role of the limpet Nacella concinna Strebel (Gastropoda: Patellidae)--Bremen, 2000.
Literaturverz. S. 94 - 108.

With the anticipated effects of climate change due to global warming, there is concern over how animals, especially ectotherms, will respond to or tolerate extreme and fluctuating environmental temperature stress. Littorinid snails are intertidal ectotherms that live high on the shore where they experience both extreme and variable conditions of temperature and desiccation stress, and are believed to live close to their tolerance limits. This study investigated the thermal biology of littorinid snails of the genera Afrolittorina, Echinolittorina and Littoraria from temperate, subtropical and tropical regions in South Africa and Brunei Darussalam using thermal tolerance, heart function, and proteome approaches. The effects of conditions, such as rate of change in temperature, acclimation, heat shock, season and starvation were also tested. In addition, the evolutionary relationships and genetic diversity between and within the South African Afrolittorina spp. were investigated using mitochondrial and nuclear markers. Genetic results confirmed that these are two distinct species, with the brown to black A. knysnaensis predominant in the cool-temperate region of South Africa and the pale blue-grey A. africana in the subtropical region. There was low genetic variation and differentiation within each species, suggesting high gene flow among populations as a result of the effects of ocean currents on the dispersal of their planktotrophic larvae. Tests using exposure to high temperatures revealed differences in the thermal tolerances, heart performance and protein profiles of species from different latitudes, regions and zones on the shore. Thermal tolerance conformed to expectations, with clear, statistically significant trends from high tolerance in subtropical species to lower tolerance in temperate species. However, for Afrolittorina spp., there were no significant differences in the thermal tolerances of conspecifics from different regions, though there was a significant difference in thermal tolerance between juveniles and adults. Overall, adults of all species showed higher thermal tolerances than juveniles. Although lethal temperatures for these species were higher in summer than winter, laboratory acclimation had no effect on heat coma temperatures. All species showed some regulation of heart rate, with a degree of independence of heart rate from temperature across mid-range temperatures. The tropical species showed quick induction and good regulation of heart rate followed by the subtropical and temperate species, which displayed mixed responses including regulation, partial regulation and lack of regulation. Overall, tropical Echinolittorina spp. showed good regulation, while the subtropical E. natalensis and Littoraria glabrata exhibited a mixture of partial regulation and regulation. The subtropical/temperate Afrolittorina spp. showed high individual variability, some animals exhibiting regulation, while others did not. These effects seem to be largely phylogenetically determined as there were no differences in the heart rate responses of Afrolittorina spp. from different regions. The temperatures at which heart rate became independent of temperature (thermoneutral zone) were within the range experienced under natural conditions. In addition, there were differences in Arrhenius breakpoint and endpoint temperatures, showing a trend from higher in tropical animals to lower for temperate animals. Conditions such as acclimation, heat shock and starvation had little or no effect on heart performance. However, a slow increase in temperature induced good regulation of heart rate with noticeable shifts of breakpoints and endpoints for Afrolittorina spp. Lastly, there were differences in the proteome responses between and within Afrolittorina spp. as a function of species, size and treatment. Although both large and small A. knysnaensis had a greater number of protein spots in their proteome than A. africana (though the difference was not significant), the later showed significantly higher differential expression of certain proteins following heat stress. In addition, juveniles of both species displayed greater numbers of protein spots in their proteome than adults. The results indicate a difference in the physiological and biochemical responses (i.e. adaptations) of these snails to temperature, and this seems to relate to differences in biogeography, phylogeny, species identity and ecology. The ability to regulate heart rate is phylogenetically determined, while thresholds and lethal limits correspond to biogeography and species ecology. The proteome seems to correspond to species ecology. The results also indicate that these littorinids can tolerate high temperature stress and in this respect they are well suited to life in the intertidal zones or habitats where temperature and other stresses or conditions are extreme and can change abruptly. However, the limited ability of these snails to acclimate to different temperatures suggests that they are already living close to their tolerance limits with small safety margins or narrow thermal windows and so may be vulnerable to small rises in substratum temperature and/or solar radiation.

"The biodiversity and ecology of marine cercariae in Australia is poorly known. Although nassariid gastropods are widely distributed in Australia and are expected to have a diverse parasite fauna similar to that of other nassariids worldwide, their cercariae have not been characterised. Nassarius dorsatus, N. olivaceus and N. pullus were collected at three separate estuarine localities in central Queensland between August 2004 and August 2006 and their emergent cercariae characterised using morphological and molecular methods. Fifteen morphotypes of cercariae from six families that infect fishes and birds as definitive hosts were characterised. The highest richness was within the Acanthocolpidae (nine morphotypes) which comprised three cercariae interpreted as species of Stephanostomum and a complex of six unusual cercariae with a ventral keel. Molecular characterisation of these six cercariae supported their placement in the Acanthocolpidae and indicated that they comprised only three species, two of which displayed marked phenotypic plasticity. Molecular analysis supported the characterisation of the three species of Stephanostomum and suggested that one of the unusual cercariae was a species of Stephanostomoides. Dissection of fish from Sandy Point provided a single match; the sequence for a metacercaria in Valamugil buchanani, the blue-tail mullet, was identical to that of one of the species of Stephanostomum. There were two cercariae from the Echinostomatidae and one from each of the Lepocreadiidae, Microphallidae, Opecoelidae and Zoogonidae. Molecular analyses supported the placement of the cercariae from the Echinostomatidae, Lepocreadiidae, Opecoelidae and Zoogonidae within their respective families. The cercaria from the Lepocreadiidae was identified by comparison to known adult data and putatively corresponds to Prodistomum keyam, a parasite of Monodactylus argenteus, the silver moony or butter bream, common in the study region. Morphological analysis supported the characterisation of both of the Echinostomatidae as species of Himasthla. Although no other cercariae could be characterised to genus level, the opecoelid cercaria was determined to be in the subfamily Opecoelinae. Nassarius olivaceus was infected by three acanthocolpid cercariae and one cercaria from each of the other families. Nassarius dorsatus was infected by five acanthocolpid cercariae and one each from the Echinostomatidae and Lepocreadiidae. Nassarius pullus was infected by a single cercaria from the Echinostomatidae. Most cercariae were specific to a single species of gastropod; only four infected two species and none infected all three. Cercariae that infect fish as a definitive host were found at all three localities; but cercariae that infect birds were restricted to a single locality, Sandy Point at Corio Bay, important for domestic and migratory bird species. These results emphasise the relative significance of Sandy Point as an important bird habitat. In total, 126 infections were diagnosed (115 by cercarial emergence), with both the highest frequency of infection and number of infections in N. olivaceus (frequency 5.3%; n=102; 81% of infections), followed by N. dorsatus (1.1%; 20; 16%) and N. pullus (0.2%; 4; 3%). The highest number of infections occurred at Sandy Point (66; 52% of infections), followed by Cawarral Creek (38; 30%) and then Ross Creek (22; 17%). The highest number of infections was by the Acanthocolpidae (54; 43%). Diagnosis of infection by emergence was suitable for all cercariae except the opecoelid, which was underdiagnosed. Nassarius olivaceus had the longest survival in captivity (~4.5 y), followed by N. dorsatus (~0.8 y) and N. pullus (~0.3 y). Almost all infections remained patent for the life of the gastropod. Families commonly found in nassariids worldwide include Acanthocolpidae, Echinostomatidae, Lepocreadiidae and Zoogonidae. Nassariid gastropods are also the dominant marine first intermediate hosts for the Acanthocolpidae, Lepocreadiidae and Zoogonidae and one of the three most common first intermediate host families for species of marine Himasthla. Molecular relationships also indicate that the Acanthocolpidae and Brachycladiidae may actually be comprised of three discrete groups, the Stephanostomum + Monostephanostomum group, the Brachycladiidae, and a group of non-Stephanostomum species comprising Pleorchis, Tormopsolus and Stephanostomoides. This research adds information about the parasite assemblages of nassariid gastropods in Australia, adding 12 new cercarial species and 16 new host-parasite records. Cercarial reports for the Acanthocolpidae, Echinostomatidae, Lepocreadiidae, Opecoelidae and Zoogonidae have been comprehensively reviewed and patterns of association between nassariids and their common parasite families presented. As well, this research has provided a potential avenue for a review of the Acanthocolpidae, a family which is currently considered a ‘catch-all’ group."

Canopy-forming seaweed are ecosystem engineers and play a central role in structuring entire communities through the amelioration of biotic and abiotic conditions and the provision of habitat. Their effects are particularly important in high-stress environments such as the intertidal zone where they provide the foundation for entire communities that would otherwise not occur there. Gastropods are among the most common group of invertebrates on intertidal rocky shores. Many species colonize seaweed canopies, or occur on the rock beneath the canopies, which reduce abiotic stress from strong wave action, high temperature, low humidity and provide a refuge from predation. While the importance of canopy-forming seaweeds as ecosystem engineers is recognised, the influence of morphological variation within intertidal seaweed species in traits such as thallus length, number and shape of structural elements on their engineering capacity and gastropod communities is not well understood. Hormosira banksii (Turner) Descaisne (Fucales, Phaeophyceae) is one of the most abundant canopy-forming species on intertidal rocky shores in southern Australasia. As with many other intertidal seaweeds, H. banksii shows a large degree of morphological variation and several morphologies are recognized across coastal and estuarine environments. While this morphological variation is likely to reflect an adaptation to differences in the tidal regime and wave action at sites, whether morphology differentially influences engineering of abiotic factors and associated gastropod communities is not well understood. This thesis examines variation in the structure of gastropod communities associated with distinct H. banksii morphologies and experimentally examines the evidence for a link between H. banksii morphology, amelioration of abiotic stress and gastropod abundance. Chapter 2 is a large-scale descriptive survey of morphological variation in H. banksii and associated gastropod communities among multiple sites occurring in different habitats (coasts and estuaries), regions (east and north) and times (February-March and October-November), in Tasmania. Three seaweed morphs were identified on the north coast (small individuals), east coast (intermediate sized individuals) and in estuaries (large individuals). Each Hormosira banksii morph supported distinct gastropod communities with a small overlap in species and two dominant species were found in the different habitats. A slight correlation occurred between H. banksii morphology and gastropod abundance, and thallus length, number and length of vesicles were the best predictors of the observed pattern. Chapter 3 investigates variation of shell morphology of the two commonest gastropod species found within the canopies of H. banksii and the link between gastropod shell size and seaweed morphology. Large and small-scale differences occurred in shell morphology for both Lunella undulata (Lightfoot, 1786) and Chlorodiloma odontis (W. Wood, 1828). A different correlation occurred between the morphology of H. banksii and the shell morphology of gastropods, suggesting a species-specific influence of seaweed morphological traits, specifically thallus length and vesicle size, on the observed patterns. Chapter 4 used two field experiments to explore the extent to which canopy cover and morphological variation of H. banksii influences engineering of key abiotic factors (temperature and irradiance) and colonisation by gastropod species. In the first experiment, canopy cover was manipulated to three levels (full [unmanipulated], half and quarter cover) and temperature, irradiance and gastropod abundance monitored. Despite any significative effect of canopy density on temperature and light levels, the full canopies supported the highest abundance of gastropods, with a species-specific colonization of the different sized canopies. In the second manipulative experiment, large (east coast) and small (north coast) morphs were transplanted to a single site and temperature, irradiance and gastropod abundance monitored for three months. The small morph of H. banksii lowered the temperature and irradiance under the canopies and supported the highest abundance of gastropods. Overall, there were weak correlations between temperature and light levels and gastropod abundance. Chapter 5 used lab experiments to examine the habitat choice of the gastropod Lunella undulata and Chlorodiloma odontis and H. banksii for different morphologies (habitat quality) and biomasses (habitat quantity) at different temperatures. There was strong variation in species behaviour, highlighting the importance of H. banksii morphology and cover in buffering temperature and providing different microhabitats to intertidal gastropods. Overall, this thesis has confirmed the importance of H. banksii as ecosystem engineer in the intertidal zone, supporting gastropod communities that differ between seaweed morphologies. However, the experimental tests of gastropod colonisation in the field and habitat choice in the lab suggest the presence of small-scale and species-specific effects of H. banksii morphology and cover on gastropod abundance, highlighting the importance of H. banksii morphological traits in determining the bioengineer potential of this species across different habitat with different environmental conditions.

Dissertação de Mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015
Foi realizado um trabalho com o intuito de compreender os padrões associados aos limites de distribuição vertical de lapas da espécie Patella depressa e analisar processos possivelmente associados a estes padrões. Para tal, realizaram-se diversos estudos relacionados com o gradiente de alturas de distribuição e com a ecologia desta espécie. A execução prática deste trabalho decorreu na zona intertidal rochosa da Praia da Oliveirinha (sudoeste de Portugal), onde é abundante a espécie em estudo. Foram efetuadas observações relativas aos limites de distribuição vertical assim como à abundância e aos padrões de movimento em dois níveis verticais de ocorrência da espécie. Também se executaram experiências manipulativas in situ para testar a variação da sobrevivência, do crescimento e da condição fisiológica das lapas em diferentes níveis verticais da zona intertidal. Observou-se um decréscimo dos limites superior e inferior de distribuição da espécie na transição do inverno para o verão. A abundância de lapas foi em geral superior no nível de maré médio comparativamente ao nível superior. Ocorreram mais deslocações no nível superior comparativamente ao nível médio. A sobrevivência e condição ecofisiológica de lapas adultas não variou entre os níveis médio e superior. Verificou-se que os indivíduos junto ao limite superior têm a capacidade de percorrer grandes distâncias e que a diminuição da altura deste limite poderá ser devido a deslocações das lapas para locais de refúgio. A mortalidade de lapas grandes no nível superior pode ser em parte influenciada pela temperatura ambiental, sugerindo a existência de estratégias de regulação de temperatura corporal possivelmente eficazes na manutenção das funções vitais destas lapas. Apesar de ter havido um particular interesse nos potenciais efeitos da temperatura na distribuição vertical da espécie há que ter em conta que outros fatores poderão estar associados às reações observadas (e.g., a humidade e disponibilidade de alimento).

Dissertação de mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2013
The present study aimed to investigate the diet and feeding activity of a sandy-mud snail, Olivella minuta along the gradient subtidal-intertidal of a dissipative morphodynamic beach: Barequeçaba (southeast coast of Brazil). Locomotor behavior of the species was also evaluated in laboratory conditions. The sampling was carried out in March, April and May, 2013 in the intertidal zone during low and high tide and in the subtidal zone during low tide, to further comparisons if these organisms change their diet according to the variation of the tide. Thirty specimens from 7 mm of length were caught in each situation and stomach contents were analyzed by means of qualitative (richness, diversity, evenness and Simpson) and quantitative indexes (numeric importance (NI) and frequency of occurrence (FO)). Also, the index of stomach repletion was calculated to complement the analysis of the feeding diet of this gastropod. A total of 49 items was registered in the digestive tracts of O. minuta being the most frequents: macroalgaes (48%), microalgaes (15%), artropodes (12%) and foraminiferans (12%). The remaining items had frequency of occurrence lower than 10%. The results of the diet composition of the individuals did not differ along the tidal range of the beach, suggesting that the species does not possess a preference for a single food resource, and the variation on NI e FO in all studied situations can be merely consequences of the dynamics of each food items during the tidal cycle. The results of the stomach repletion suggest that this snail feed in all studied situations, but with higher intensity when emerged during low tide and the results of locomotor behavior tested experimentally, reinforce this idea and still suggests that during the day this organisms have a higher feeding activity rather than at night, since a lesser movement was displayed in these conditions.
As praias arenosas são dos ambientes mais hostis para as comunidades de organismos bentónicos. Estas áreas estão sujeitas a uma enorme intensidade de factores que as moldam morfologicamente ao longo do tempo e que, consequentemente, afectam a distribuição e o comportamento dos organismos que nelas ocorrem. O dinamismo ambiental, resultado da variação de parâmetros abióticos, tais como regime de ventos, ondas, correntes e marés, com consequentes alterações na morfodinâmica da praia, leva os organismos intertidais a desenvolverem adaptações morfológicas, fisiológicas e comportamentais que os permitem suportar o dinamismo do ambiente costeiro. Dito isto, acredita-se que a estrutura de comunidades e populações em praias arenosas é determinada pela morfodinâmica, na qual os factores físicos são predominantes. De acordo com a Hipótese de Severidade Ambiental (HSA) para praias arenosas, as populações de praias reflectivas deverão exibir menor abundância, crescimento, fecundidade e maior esforço reprodutivo e maior taxa de mortalidade quando comparadas a populações de praias dissipativas, uma vez que o impacto de facotes abióticos em praias dissipativas é considerado reduzido, fornecendo aos organismos estabilidade para o seu estabelecimento nestes ambientes. O conhecimento sobre como a interacção de factores bióticos e abióticos pode modular a distribuição de uma espécie, são fundamentais para entender a dinâmica e ecologia da população em um ecossistema de praia. Além disso, a análise da dieta, através da análise do conteúdo do estômago, é uma ferramenta importante para a compreensão da ecologia de uma comunidade, pois além de nos fornecer dados de como as espécies se sobrepõem no uso de recursos alimentares, a interacção dos mecanismos biológicos das espécies em uma comunidade também é observada. Deste modo, a análise do conteúdo estomacal, torna-se uma ferramenta importante para validar a importância da posição trófica de um predador particular no fluxo de energia de um ecossistema, bem como determinar a estratégia de alimentação e da composição de alimentação. Gastrópodes têm uma grande quantidade de hábitos alimentares, podendo ser detritívoros, necrófagos, predatórios, herbívoros, e muitos são omnívoros. Em muitos fundos moles, as suas actividades alimentares são conhecidas por afectar a estrutura da comunidade, especialmente macro e meiofauna. Por outro lado, são esperadas variações dentro das populações desde que os recursos tornam-se fonte de heterogeneidade na distribuição e abundância dos organismos. Assim sendo, neste estudo foram avaliados quais os efeitos dos ciclos de maré bem como diurno/nocturno, na dieta alimentar e actividade locomotória do gastrópode Olivella minuta, numa praia arenosa de baixa energia dissipativa, Praia de Barequeçaba, localizada no Litoral Norte do Estado de São Paulo (Brasil), tendo como base, a HSA. As amostragens foram realizadas tanto em condições de submersão, (na zona intertidal durante maré alta e no subtidal durante maré baixa) com o auxilio de um puçá, bem como quando sujeitos à exposição do ar (no intertidal durante maré baixa), através das marcas sinuosas deixadas por este predador no sedimento. Trinta indivíduos com comprimento de concha igual a 7 mm foram amostrados em cada situação e os seus conteúdos estomacais foram analisados tanto por métodos quantitativos (importância numérica (NI) e frequência de ocorrência (FO)), bem como por meio de análises qualitativas, através da determinação dos índices de diversidade de Shannon, equitabilidade de Pielou, dominância de Simpson e Riqueza de espécies. O índice de repleção estomacal mostrou actividade alimentar desta espécie em todas as situações, com um acentuado pico de actividade quando exposta a períodos de maré baixa. Um total de 49 itens alimentares foi registado no trato digestivo de O. minuta, sendo macroalgas (48%), microalgas (15%), artrópodes (12%) e foraminíferos (12%) os recursos mais consumidos por este gastrópode. Itens alimentares com proporções inferiores a 10% também foram identificados nos estômagos deste gastrópode, tal como itens indeterminados (7%), Porífera (3%), vermes (2%) e moluscos e ciliados ambos com 1% de NI. Bactérias foram também identificadas na dieta alimentar de O. minuta mas não apresentaram importância significativa na composição alimentar deste gastrópode. A maré não mostrou ser factor chave na selectividade alimentar de O. minuta, dado que a composição alimentar destes organismos não se mostrou significativamente variável entre as três situações estudadas (Intertidal durante maré alta, intertidal durante maré baixa e zona subtidal), onde macroalgas e foraminíferos foram os itens alimentares mais abundantes nos estômagos deste organismo em cada situação particular estudada. Os resultados sugerem que a espécie não possui uma preferência por uma única fonte de alimento, e a variação dos valores de NI e FO ao longo das situações pode ser meramente consequências da dinâmica de cada um dos itens alimentares face ao ciclo das marés. Também a fase de maré não se mostrou relevante na actividade locomotora de O. minuta. Por outro lado, o ciclo dia / noite simulado em condições de laboratório mostrou grande significância, onde menores percursos foram observados nos tratamentos sujeitos a períodos de dia. Estudos prévios realizados em gastrópodes sobre o seu comportamento locomotor associado a alimentação, leva-nos a reforçar a hipótese proposta neste estudo, em que o comportamento locomotor de O. minuta é influenciado pela disponibilidade de recursos alimentares no ambiente. Os resultados do nosso experimento laboratorial reforçam a ideia de que estes organismos quando emersos e durante períodos de maré baixa apresentam uma maior actividade alimentar, essencial para a manutenção dos seus recursos vitais, tais como crescimento e reprodução. Também o enterramento em profundidade no sedimento durante o dia, como foi observado em laboratório, pode ser um mecanismo de defesa contra a dessecação e predação. Os resultados deste estudo vão de acordo com a hipótese da severidade ambiental para praias protegidas, morfodinâmicamente dissipativas, como foi modelo deste estudo, praia de Barequeçaba. Neste extremo dissipativo, a influência de factores abióticos (neste caso o ciclo de marés), não mostrou ser o factor mais importante nas funções vitais (alimentação e deslocamento) deste gastrópode. O seu comportamento (diurno e enterramento no sedimento) sugere uma possível adaptação destes organismos de forma a evitar a predação bem como uma forma de maximizar a qualidade ou quantidade de alimento disponível no local quando expostos ao ar e á luz em ambientes arenosos.