Organisms occupying an environment where change is occurring must move, acclimatise, or adapt in order to prevent extinction. Despite recent evidence, the potential for species to change their distribution range across depths is regularly overlooked as an alternative to well documented latitudinal shifts. The aim of this thesis was to investigate the physiological viability of bathymetric range shifts by assessing the impacts of elevated hydrostatic pressure (HP) and changing temperature in two marine ectotherms: the shallow-water caridean shrimp Palaemonetes varians; and the continental slope-depth anomuran crab Lithodes maja. Gene biomarkers were characterised in both species and their transcriptional regulation was assessed by qPCR. Acute and long-term exposures revealed that elevated HP produced significant perturbations at the transcriptional level in P. varians, and were corroborated by measurements of behaviour and respiratory response. HP-associated pathologies were exacerbated by decreasing temperature, and ameliorated by increasing temperature. Results gave a novel insight into the hierarchy and kinetics of HP-induced stress responses, and suggested that the combination of HP and temperature, in part, determines the physiological limitations to bathymetric migration in shallow-water ectotherms. To further test the role of HP and temperature in setting depth distribution limits, gene biomarkers were characterised in a continental slope-depth crab Lithodes maja. Transcriptional regulation and respiration rate was quantified throughout larval ontogeny, and in mature adults. Early life stages showed HP tolerance beyond that of the species natural distribution limits. The observed HP tolerance window reduced through ontogeny. Reductions in HP tolerance with life stage may be analogous to established thermal tolerance reductions with ontogeny. Further, sustained HP exposures suggest that bathymetric range limits in L. maja are constrained by increased metabolic costs, nervous system sensitivities, and macromolecular damage under elevated HP. HP and temperature, and particularly the combination of the two, play an important role in setting the depth distribution limits of marine ectotherms. For temperate shallow-water adapted marine ectotherms, water temperatures towards the upper limit of their thermal scope may facilitate bathymetric range shifts, whilst colder waters further exacerbate the negative physiological effects of elevated HP. Bathymetric range shifts may, under certain scenarios, offer an important, yet underestimated, alternative to latitudinal shifts in light of contemporary climate change. Further, the combination of HP and temperature may have played an important role in the colonisation of the deep sea from shallow waters by marine ectotherms.

Marine dinoflagellates are an ecologically important phytoplanktonic group that accounts for two thirds of all known harmful algal bloom (HAB) species. This study explores the population ecology of Lingulodinium polyedrum (F. Stein) J.D. Dodge, a common bloom-forming dinoflagellate species in Southern California. Lingulodinium polyedrum is not considered a HAB species, but functions as one of the main model organisms for dinoflagellate biology. As such, knowledge about this species also contributes significantly to the understanding of dinoflagellate population dynamics at a more general level. In an attempt to understand some of the complex interactions that govern L. polyedrum population ecology, laboratory experiments of life cycle control and intraspecific phenotypic diversity were linked with an in situ study of the population dynamics and the intraspecific genetic diversity of this species in coastal waters of Southern California. The life cycle experiments showed that processes such as gametogenesis and ecdysis of L. polyedrum are influenced by photon flux density (PFD) and gave a first indication for an involvement of the photosynthetic apparatus in the induction of gametogenesis in dinoflagellates. The light acclimation experiments revealed, for the first time, intraspecific phenotypic diversity in L. polyedrum. The two studied strains differed distinctly in their light requirements and light acclimation ‘strategies’. For the study of intraspecific genetic diversity in L. polyedrum a novel method was developed that allowed the genotyping of individual cells. The application of this novel approach to natural populations showed that population genetic exchange of L. polyedrum in the Southern California Bight is tied to water circulation patterns and that both habitat structure and environmental change leave their signatures in the population genetic composition of L. polyedrum. This thesis represents one of the most comprehensive studies of dinoflagellate population ecology and builds the basis for the development of a holistic concept of the population ecology of L. polyedrum and other dinoflagellate species.

No description available.

No description available.

The precarious status of flat oyster Ostrea edulis stocks in Europe is widely acknowledged. To build a scientific basis for oyster restoration, an elevated experimental reef stocked with O. edulis was established within Poole Bay (Dorset, UK). Oysters were planted out on twenty four oyster reef modules (80cm above sea bed) and compared with oysters held on the sea bed close to each reef module to test the hypothesis that a reef habitat enhances physiological performance of O. edulis and improves local biodiversity. The environmental data indicated that there was no significant difference in temperature or salinity between the elevated reefs and sea bed. Whilst total suspended solids were significantly higher at the sea bed than at 80 cm above the sea bed at every sampling interval. The filtration rates of oysters varied with elevation (reef/sea bed) and months. Filtration rates of reef oysters were significantly higher than sea bed oysters. Respiration rates varied among months but were not significantly affected by elevation. Elevation and month also affected the total number of haemocytes and the granulocyte population; reef oysters had significantly higher numbers of haemocytes than sea bed oysters. Althought geographical variation in filtration rate was also observed, this study suggested that the improved physiology of reef oysters in summer was still notable when comparing between different populations. An increase in filtration rate for reef oysters may, however, increase the likelihood of uptake of the protozoan parasite, Bonamia sp. However, haemocyte and haemolymph protein data suggested that there was no differential impact on physiology between reef and sea bed oysters as a result of Bonamia sp. infection. Fifty-four epifaunal species including oyster spat were found on oyster valves in reef boxes whilst only 23 species with no oyster spat were found on oyster valves in oyster cages laid on sea bed. The epifaunal community on oyster valves on reefs was significantly different from those sea bed valves but also had some species in common. Sixty-five mobile species were observed in reef boxes, whilst 47 species were recorded in oyster cages. These differences in faunal communities observed on the elevated reefs and sea bed implied that the presence of elevated reef habitats created by O. edulis valves can enhance or accelerate local diversity in Poole Bay. As current stocks of European flat oysters (O. edulis) in Europe have declined in both abundance and distribution, the results of this pilot study suggest that the culture of oysters on elevated reef structure represents at least a partial solution to improve O. edulis physiology for restoration in Europe.

Emiliania huxleyi is a ubiquitous coccolithophore present throughout the global ocean and capable of forming large blooms with significant effects on the global carbon cycle. Developing our understanding of E. huxleyi ecology is necessary in order to better quantify E. huxleyi’s role in the present carbon cycle, and to predict its role in the future carbon cycle under climate change scenarios. Major gaps in the understanding of E. huxleyi ecology were addressed using (1) controlled mesocosm experiments in June 2008 in Raunefjord, Norway, to map population genetics of E. huxleyi blooms in relation to ecological pressures (viruses and rapid growth), (2) biogeographic sampling of nannoplankton (2 - 20 μm) in the SO, including E. huxleyi, to determine ecological pressures on E. huxleyi blooms in situ (environmental gradients), and (3) controlled iron (Fe) addition bioassay experiments in the SO to establish the role of Fe gradients in the nannoplankton community relative to the phytoplankton community. During the mesocosm experiments, 279 individual E. huxleyi cells were isolated to establish clonal cultures, of which 143 were successfully genotyped using 5 microsatellite molecular markers. Both high gene diversity and two distinct genotypic populations were detected over the bloom time series and are strong evidence for a large reservoir of genetic variability within the E. huxleyi species concept, which may translate into phenotypic plasticity, such as differing levels of viral resistance. In the SO, the spatial and temporal biogeography of the three most numerous mineralizing nannoplankton groups, the coccolithophore E. huxleyi, the smaller (<20 μm) species of the diatom genus Fragilariopsis, and chrysophytes of the genus Tetraparma were defined using scanning electron microscopy (SEM) analysis in conjunction with an array of biological, physical, and chemical variables during two successive cruises to the Scotia Sea. Multivariate statistical analyses were used to identify the most influential environmental variables controlling mineralizing nannoplankton biogeography. Sea surface temperature (SST) and salinity were identified as primary variables and removed from the analysis, leaving frontal boundaries, macronutrient, and dFe concentrations significantly associated with a northern E. huxleyi-dominated community (group I; higher nutrients) and a southern Tetraparma- and Fragilariopsisdominated community (group II; lower nutrients). Estimates of biomass indicated that the Scotia Sea mineralizing nannoplankton community formed a substantial part (on average 13%) of the total phytoplankton community. The results of bioassay Fe incubations indicated a response in medium and large diatoms and E. huxleyi, and a number of microplankton (20 – 200 μm) diatom species. Overall, the work contributes substantially to our understanding of the molecular population structure, extent of phenotypic plasticity, and environmental parameters affecting the key phytoplankton E. huxleyi.

Coccolithophores are a unique group of calcifying phytoplankton that dominate pelagic biogenic calcification and facilitate carbon export. Changes in coccolithophore calcite production through changes in their abundance, species distribution or cellular calcification could affect the oceanic carbon cycle. Ocean acidification, global warming and future changes in nutrient and light conditions might affect coccolithophore populations. This study investigated the relationships between coccolithophore distribution and calcification and environmental factors, between the North Sea and the Arctic Ocean and in the Southern Ocean. Large gradients in carbonate chemistry and other variables provided insights into coccolithophore response to concurrent changes in the future ocean. Freshwater inputs and biological processes were driving the carbonate chemistry changes in the surface waters of the North Sea, the Norwegian Sea and the Svalbard Arctic region. Even though biological processes seemed to play a major role in shaping the saturation state (calcite) and pH of these regions, the carbonate chemistry of the freshwater sources (Baltic Sea, sea-ice melt, riverine input/ terrestrial runoff) was also important and had accentuated the effects of biological activity. A multivariate approach showed that changes in pH and mixed layer irradiance explained most of the variation in coccolithophore distribution and community composition between the North Sea and Svalbard. Differences between the Svalbard population (dominated by the family Papposphaeraceae) and those from other regions were mostly explained by pH, whereas mixed layer irradiance explained most of the variation between the North Sea, Norwegian Sea and Arctic water assemblages. Estimates of cell specific calcification rates showed that species composition can considerably affect community calcification. At Drake Passage, the coccolithophore community was dominated by Emiliania huxleyi B/C. Diversity and abundance were highest in the Subantarctic and Polar Frontal Zones, respectively, where temperature and mixed layer irradiance were high. Community and cell specific calcification, as well as coccolith production rates, showed an overall decreasing trend towards Antarctica and were correlated with the strong latitudinal gradients in temperature and calcite and anti-correlated with nutrient concentrations. Additionally, coccolith production rates and cell specific calcification were also correlated with mixed layer irradiance. Coccolithophore calcification rates at Svalbard and at Drake Passage were low compared to other oceanic regions. At Svalbard, the low calcification rates were the result of very low abundances of species that have both a low (e.g. Papposphaeraceae) and high (e.g. Coccolithus pelagicus) calcite content. At Drake Passage low calcification rates were the result of low to moderate abundances of E. huxleyi B/C, which has a low calcite content. The results of this study suggest that changes in future pelagic calcite production may result from physiological changes acting on single species and/or from shifts in the species composition of coccolithophore assemblages, as well as poleward biome migrations induced by ocean acidification, sea surface warming and stratification.

This research provides a new method to identify likely marine feeding grounds for migratory pelagic species that are problematic to directly study at sea. The method is based on stable isotope compositions of tissues that may be sampled without harming the target animals, and can be conducted retrospectively from tissue archives. The wild Atlantic salmon has been in steep decline throughout its native range over the past four decades, largely due to increases in marine mortality. This research investigated potential causes of this decline using stable isotope analysis of archived scale samples, taken from returning adult salmon over the past few decades. Investigations of UK scale holdings identified the River Frome and Northeast Coast Driftnet Fishery archives as the most available and useful, giving good spatial contrast and temporal coverage. After developing sampling and analytical protocols, carbon and nitrogen isotopic composition was measured in grilse (one-sea winter) and multi-sea winter (MSW) salmon scale samples taken from both archives over 23 and 14 years. Analyses were performed on the last marine growth season, giving a retrospective record of marine conditions experienced by each fish. Both isotopes are influenced by baseline environmental conditions, and climatic effects are found to exert strong controls on numbers of fish returning to both the Northeast Coast and River Frome populations. Trophic level and/or baseline nitrate effects are also found to influence returning abundance to these populations, although more strongly in the Frome. Yearly d13C values were correlated with median yearly sea surface temperature values for each degree of latitude and longitude across the North Atlantic, and maps produced of the correlation strengths. These maps suggest likely feeding grounds for each cohort within each population, with the River Frome grilse and MSW salmon respectively feeding near the shelf breaks of northeast and southwest Iceland. The Northeast Coast grilse and MSW salmon were, in contrast, feeding near the shelf breaks of the southern Norwegian Sea and the Bear Island Trench in the northern Norwegian Sea, respectively.

Most studies of deep-sea benthic fauna have concentrated on soft sediments with little sampling in rocky areas and even less on non-vent mid-ocean ridges and within submarine canyons, mainly as a result of difficulty accessing them. To assess the distribution and abundance of cold-water corals along an Axial Volcanic Ridges along the Mid-Atlantic ridge at 45oN 27oW, and within the Whittard Canyon along the Irish Margin video footage from the ROV Isis taken during a three scientific cruises was analysed. Samples were also taken to allow taxonomic and phylogentic work to be completed. Abundance of octocorals per 100 m transect were calculated and mapped using Arc GIS, with a maximum of 59 in the AVR compared to 855 within the Whittard Canyon. Thirty-one putative species were identified within the Whittard Canyon including some scleractinians, Eleven more than were found in along the AVR. Both locations indicated differences in coral assemblages dependent on substratum type with sedimented areas having increased occurrence of Pennatulidae and Chrysogorgiidae within the AVR and an increased abundance of Acanella and Radicipes upon sediment in comparison to rock within the Whittard Canyon. It is suggested that these differences in abundance and assemblage structure, both within and between the AVR and Whittard Canyon sites, reflects higher food availability as well as differences in substratum type on which coral larvae settle. Taxononomic investigations identified 4 new species from samples taken along the AVR, and are described within the thesis. Phylogenetic analysis of novel sequences obtained throughout this study, as well as published sequences, showed the presence of 3 clades A) Calcaxonia and some Alcyoniidae B) Holoaxonia and Pennatulacea C) some Alcyoniidae, Corallium and Paragorgia. When individual MSH1 and ND2 genes were combined the Pennatulacea separated out as a fourth clade. This was attributed to an increase in resolution when two or more genes are used for analysis. Results indicate that morphological taxonomy and molecular analysis are not in agreement and there is a requirement for some taxonomic revisions using molecular data to confirm species boundaries and help guide taxonomic decisions.

No description available.