No description available.

Gromiids are large amoeboid protozoans with an organic test and filose pseudopodia, which protrude through a shell aperture that is surrounded by an oral capsule. The first shallow-water gromiid, Gromia oviformis, was described by Dujardin in 1835 and is found worldwide. It was only in 1994, however, that gromiids were found for the first time at bathyal depths in a nonfjord setting, when the first deep-sea gromiid, G. sphaerica, was recovered from below the oxygen minimum zone on the continental slope off Oman in the Arabian Sea. The present study is based on the largest sample set of undescribed deep-sea gromiids thus far. The core of this thesis is the description of twelve new morphospecies from bathyal and abyssal depths (1180 m – 4800 m) in the Weddell Sea, Antarctica, using a combination of morphological and molecular criteria. All species possess a distinct oral capsule and a layer of “honeycomb membranes”, which form the inner part of the organic test wall. Both these features are characteristic of gromiids. Their identification as gromiids is confirmed by analyses of partial small subunit ribosomal DNA (SSU rDNA) gene sequences for three of the twelve new species: Gromia marmorea sp. nov., Gromia melinus sp. nov., and Gromia winnetoui sp. nov. Phylogenetic analysis using the maximum likelihood method revealed that G. marmorea and G. melinus form two distinct clades reflecting the morphological differences amongst the Weddell Sea species, and between deep-water Southern Ocean Gromia and previously described shallow-water gromiid G. oviformis, as well as gromiids from the deep Arabian Sea. Gromia winnetoui forms a third clade which branches with one of the Arabian Sea species. Both these species are morphologically very distinct and therefore the molecular results are inconsistent with the morphological characteristics. Based solely on morphological criteria, another sixteen morphospecies from the Northeast Atlantic are described, including specimens from the Northwest African margin (1320 m), the Porcupine Seabight and the Rockall Trough (1028- 3000 m), the Skagerrak (664 m), and the fjords of Møre along the western coast of Norway (65- 667 m). Most deep-sea gromiids appear to range in size between 0.1 and 4.0 mm, except for morphospecies B2 from the Skagerrak as well as most of the Arabian Sea species, which display a wider size range. The different morphospecies exhibit a variety of shapes, including spherical, droplet, conical, grape, elongate oval, sausage, bowling pin, vermiform, and irregular. The results of this thesis support the hypothesis that gromiids occur at depths >200 m in all major oceans. They are predominantly found along continental margins between 1000 and 3000 m. This thesis presents the only two records of Gromia (G. melinus and Species 154) from depths >4000 m in the Weddell Sea. It is hypothesized that further sampling will increase the number of species and novel morphotypes. Gromiids appear to be found in highest abundances in areas with elevated fluxes of organic matter. They are likely to play an important role in carbon and nitrogen cycling, as well as increasing local biodiversity.

Much of the primary production in northern latitudes is associated with the relatively short spring phytoplankton bloom. Quantifying the bloom is essential to understanding export production and energy transfer to higher trophic levels. This study focuses on the physical forcing controlling the spring bloom in the Irminger Basin (IB), situated between Greenland and Iceland. In situ data are available from four cruises to the region carried out under the UK Marine Productivity programme. This data set is extended with six years of SeaWiFS satellite chlorophyll-a concentration (chl-a) data, together with the corresponding model net heat flux (NCEP reanalysis) and satellite measured wind speed (QuikSCAT), sea surface temperature (SST; AVHRR) and photosynthetically available radiation (PAR; SeaWiFS). The remotely sensed data are complemented by a 1-D vertical mixing model and temperature and salinity profiles from Argo drifting profilers. The seasonality in temperature-nutrient (TN) relationships is investigated and the TN relationships are improved by including chlorophyll in the regressions. Basin-wide, daily estimates of nitrate, phosphate and silicate are made from satellite SST and chl-a. The study focuses on three biogeographical zones determined by cluster and Empirical Orthogonal Function analysis of SeaWiFS chl-a data. The three areas have distinct chl-a signatures and cover the East Greenland shelf, the Reykjanes Ridge and the Central Basin. An ANOVA analysis reveals that significant interannual variability is occurring in chlorophyll-a. An objective method for determining the start day of the spring bloom is described. Interannual variability in the timing of the initiation of the bloom and its magnitude and duration is discussed. The influence of the prevailing meteorology on chl-a in different seasons are investigated using generalized linear modelling. Whilst net heat flux and PAR are the dominating factors in spring, wind speed and SST become increasingly influential during summer and autumn. A method for estimating time series of Sverdrup’s critical depth from remotely sensed PAR and attenuation coefficient data is outlined. It is found that the spring bloom never begins before the mixed layer depth becomes shallower than the critical depth, and there is a delay of ~10 days. Specific criteria for the start of the bloom in terms of net heat flux and PAR are determined. The effect of nutrient depletion on the decline of the bloom is discussed. The East Greenland coastal zone is used as an example of the lasting impact that anomalous meteorological conditions can have on the following spring’s bloom. In 2002 the East Greenland region experienced anomalously low chl-a concentrations. Strong easterly winds, associated with the tip-jet phenomena, occurred throughout winter and spring and net heat flux was anomalously low in 2002. The spring bloom in the Irminger Basin can be affected by large scale climatic events, such as shifts in the North Atlantic Oscillation. Finally, the timing of nutrient depletion and its impact on community succession is considered. The possibility of iron limitation in the basin is discussed. A lower bound estimate of export production is made based on the timing of silica availability, and hence diatom dominance, of the spring bloom. The contributions to export production by diatoms and non-diatoms are estimated.

The Bermuda Atlantic Time-series Study (BATS) site represents a unique hydrographical oceanic environment to study the factors controlling bacterial growth dynamics. The region was sampled at monthly intervals from 1991 to 1996. A typical annual cycle was defined by a deep winter mixing, followed by an increasing stratification of the mixed layer through summer and fall. There were striking seasonal patterns in phytoplankton productivity with a strong maximum immediately following the deep winter mixing and the intrusion of inorganic nutrients. Bacterial growth rates showed a similar pattern but had a secondary peak in late summer/fall of the same magnitude as the spring bloom. Bacterial abundance showed only slightly elevated concentrations in spring. A number of time course storage experiments showed that bacterial abundance decreased by 24-50 % within 7-29 days in samples preserved with 2.5 % glutaraldehyde. By adding a protease inhibitor prior to the addition of glutaraldehyde, the loss of bacterial cells was reduced to 17-18 % over a 30 day period. These findings lead to the recommendation that samples for bacterial abundance should be processed immediately for epifluorescence enumeration. An average of 47 % of all bacterial cells passed the pore size of a Whatman GF/F filter and these viable cells should be included in biomass estimates. An annual average of 26 % of estimated C settled below the spigot of a Niskin water sampler. Consequently, C measurements made on GF/F filters must account for the particles settling below the spigot of a water sampler as well as the number of bacteria lost during the process of filtration. This study is the first to present single cell elemental C, N and P measurements from natural bacteria in the Sargasso Sea. A wide range in elemental content was found between single cells and this could be expressed as a function of the cell size. By applying an average cell volume, an annual average of 10 fg C, 1.9 fg N and 0.28 fg P was calculated per bacterial cell. The average percentage integrated stocks of C in the upper 250 m of the water column, was 20 (phytoplankton), 18 (microheterotrophs) and 62 (other non-living detrital matter). Bacterial biomass was higher than phytoplankton outside the spring bloom period, but non-living carbon showed an overall dominance through out the year. Phytoplankton generation time was relatively constant over the season. Bacterial generation time was ten times longer and showed a greater seasonal variation, but largely followed the changes in primary production. Assuming that 50-70 % of the bacterial cells were non-living, the mean bacterial generation time was estimated to be 7 times (0-60 m) and 1.4 times (80-140 m) longer than phytoplankton generation time. During the spring bloom event, an average of 85 % of the bacterial growth rate was removed by grazing and viral lysis. This was the only noted decoupling between growth and removal of bacteria at BATS. During the remainder of the year bacterial growth was balanced by the loss rate, due to grazing and viral lysis. A linear relationship was found between net DOC accumulation and primary production in natural surface waters at BATS. Phytoplankton net DOC excretion constituted 42 % of the primary production rate, while Trichodesmium colonies only excreted 12 % (puffs) and 23 % (tufts). By using a conservative estimate of the bacterial growth efficiency (14 %) and the net DOC accumulation rate from this study, gross DOC excretion was equivalent to the rate of primary particulate C production. Results from this study suggests that bacteria at the BATS site are using the majority of the DOC generated by primary production. Prior to the spring bloom and the associated increase in DOC excretion, bacteria appeared to be C limited in the surface waters at BATS. Following the peak in primary production and coinciding with the depletion of inorganic nutrients in the euphotic zone, the bacterial cells became less C starved, but never reached a true N or P limitation. Regenerated nutrients from grazing and viral lysis of bacteria and new production by diazotrophic Trichodesmium colonies and trichomes, may support the bacteria with N and P in the euphotic zone in summer and fall. The substrate dependent growth and increase in biomass of bacteria exhibited at BATS in spring, is indicative of a bottom-up controlled system, whereas the bacteria appeared to be topdown controlled by grazing and viral lysis for the remainder of the year.

No description available.

Deep-sea hydrothermal vents and cold seeps are remarkable for their spectacular megaand macrofauna, many of which appear to have a high level of endemism to these chemosynthetic environments. It is not clear whether the patterns of biodiversity, faunal zonation and biogeography documented in these size categories, are also present in the meiofauna. This thesis examines the diversity and density patterns of the meiofauna (with particular reference to nematodes) in quantitative samples collected from: Bathymodiolus mussel beds in a deep-sea hydrothermal vent field on the East Pacific Rise; Bathymodiolus mussel beds at an Atlantic methane seep site; an Atlantic hydrothermal vent sediment mound and a reference non-chemosynthetic sediment site on the Mid-Atlantic Ridge. Results suggested that deep-water chemosynthetic substrata will generally harbour assemblages exhibiting lower diversity and elevated dominance. The densities of meiobenthos appeared to vary in accordance with the presence of macrofauna. From the study of the meiobenthos of hydrothermal vent mussel beds spanning 27 degrees of latitude on the EPR, the nematodes share the same, if not a larger biogeographical province as the macrofauna. From comparison of data collected from the vent mussel beds and the Atlantic methane seep mussel bed, it was evident that the species composition of the nematode assemblage was completely different. Density levels and major taxa composition were very similar as a result of similar local factors acting within the mussel beds. Based on a comparison of data collected from all mussel bed samples and the hydrothermal sediment core, it was evident that the nematode assemblages were significantly different. Factors determining all the observed differences are discussed.

No description available.

Patterns in polychaete abundance, body size and diversity were investigated at 12 sites between 4300 and 5000 m in the central Pacific and the north-east Atlantic. In the central Pacific, three of the sites (EqPac 0N, 2N and 5N) were observed to lie under high surface productivity regimes, and they were known to receive significant accumulations of food-rich phytodetrital material. The EqPac 9N, HOT 23N, DOMES A, ECHO 1 and PRA sites, which did not receive phytodetritus, were used as control sites with which to investigate the effect of this phytodetrital input. In the north Atlantic, one of the sites (PAP) was known to receive phytodetrital input, and one of the sites (MAP) had been subjected to a large-scale natural disturbance in the form of a turbidite emplacement. All specimens were identified to species level. Two families, the Pilargidae and Cirratulidae were selected for a more detailed alpha taxonomy assessment. New characters were developed for the identification of cirratulid thoracic fragments. Benthic polychaete abundance was correlated with surface productivity in both the Pacific and Atlantic Oceans. There was some evidence to suggest that there was a stronger benthic-pelagic link in the Pacific Ocean, where small changes in surface productivity generated larger changes in abundance than in the Atlantic Ocean. When data from previous studies are included, it is suggested that at levels of surface productivity above 200 gCm'2yr4, there is an upper limit to benthic polychaete abundance. Significant differences in body size between sites were found at species level, family level and for the entire polychaete taxon. At a species level, several abundant cosmopolitan deposit feeding species showed reduced body size in the food-rich phytodetrital sites. The only species to show increased body size in the food-rich sites were two predatory species. Polychaetes in the Atlantic Ocean responded more strongly in terms of body size reduction in phytodetrital sites than they did in the EqPac sites. Three hypotheses were put forward to explain these patterns: increased metabolic efficiency of large organisms in food-poor regions, seasonal recruitment pulses at phytodetrital sites and increased competition at phytodetrital sites. The former was favoured as the most likely explanation. Species diversity was shown to be highest in the phytodetrital sites in the central Pacific. It was hypothesised that this was the result of increased productivity, increased spatio-temporal heterogeneity and increased sediment heterogeneity at these sites. An increase in species diversity at phytodetrital Atlantic sites was not observed. The differences between north Atlantic and central Pacific sites were attributed to regional enrichment of local diversity in the Pacific. At the MAP turbidite site, alpha diversity was significantly lower than at other sites, and dominance was high, indicating the potential for large-scale natural disturbance in the abyss. A new spatio-temporal scale of disturbance was highlighted that may have evolutionary as well as ecological significance. Although levels of alpha diversity were generally shown to be high in the abyss compared to shallow water, the evidence did not suggest in favour of high beta diversity on scales of 1000 to 3000 km in either the central Pacific or north Atlantic. The low levels of beta diversity observed suggest that total species richness in the deep sea may not be as high as previously hypothesised, and that regional processes are likely to significantly impact local ecology in the deep-sea.

Lipids are a group of biologically important compounds that may be used as indicators of relationships between an organism and its environment. Lipid class composition identifies types of storage lipid which can suggest a pelagic or benthic existence and may be used to measure the condition of an organism. Fatty acid composition may reflect trophic ecology. Lipid profiling has been used to elucidate elements of the ecology of organisms from Mid-Atlantic and Juan de Fuca Ridge hydrothermal vents and shrimp from below a permanent oxygen minimum zone. Lipid profiles of these organisms from extreme deep-sea environments are compared. Lipid profiles of adult Mid-Atlantic Ridge hydrothermal vent shrimp, Rimicaris exoculata. support a benthic existence and primarily chemoautotrophic bacterial nutrition. Postlarval alvinocarid shrimp lipid profiles suggest a pelagic life cycle stage with a reliance on phototrophically derived organic matter. This result supports previous molecular evidence that Rimicaris exoculata travels between hydrothermal vents on the Mid-Atlantic Ridge. The branchial area of Rimicaris exoculata has been reported to be colonised with bacteria and elevated levels of bacterial fatty acids are present in these tissues. Lipid analyses of the reproductive organs of Rimicaris exoculata reveal increases in triglycerides, sterols, phosphatidyl choline and the proportion of n-3 fatty acids with advancing reproductive maturity. Preliminary studies of the lipid profiles of the Mid-Atlantic vent shrimp Alvinocaris markensis support the hypothesis that it is a scavenger and contains a lower proportion of bacterially derived fatty acids. The lipid profiles of the deep-sea shrimp, Nematocarcinus gracilis, from the Indian Ocean, were consistent with a benthic lifestyle, opportunistic feeding and a reliance on phototrophically derived organic matter. Despite the presence of a permanent oxygen minimum zone above the habitat of the shrimp, Nematocarcinus gracilis contain low levels of highly unsaturated fatty acids, reflecting a reduction in the availability of labile organic matter with depth. The hydrothermal vent tube worm Ridgeia piscesae contains only low levels of storage lipid, reflecting an extreme reliance on endosymbiotic bacteria. Wax esters detected are thought to be stored in oocytes. The fatty acid profile of Ridgeia piscesae reveal mainly bacterial biomarker fatty acids, but some phototrophically derived fatty acids are also present. Adult Ridgeia piscesae have no gut, so the mechanism by which these fatty acids are assimilated is uncertain. Lipid profiles of the hydrothermal vent palm worm, Paralvinella palmiformis vary with the conditions of the different microenvironments in which specimens were found. Fatty acids reflect a mixed diet based mainly on chemoautotrophic bacteria, but with significant inputs of phototrophically derived organic matter, such as diatom debris. Phototrophically derived fatty acids were also detected in the hydrothermal vent clam Calyptogena pacifica. suggesting that the reduced filter-feeding ability of this species is used to supplement nutrition from endosymbiotic bacteria. Endosymbiont-bearing gill tissues contain the highest proportion of bacterial fatty acids and also high concentrations of triglycerides. The presence of triglycerides in gill tissues suggests that energy may be transferred from symbionts by hydrolysis of bacterial symbiont membrane lipids and their conversion to triglyceride. The lipid profiles presented in this work increase understanding of the life history strategies and ecology of the species studied. This thesis shows that even the most highly adapted hydrothermal vent organisms do not rely solely on a chemoautotrophic source of nutrition, but also appear to require phototrophically derived elements in their diet.

Ship-board experiments in the North Atlantic were used to study how food quality influences the egg production of Calanus finmarchicus feeding on natural planktonic diets. Food quality was expressed in terms of carbon (C), nitrogen (N), and the essential fatty acids eicosapentaenoic acid (EPA; 20:5(n-3)) and docosahexaenoic acid (DHA; 22:6(n-3)). Five consecutive 24 hr bottle incubations were conducted in April and July/August 2002 under in situ conditions to determine egg production rates and the ingested quantities of C, N, EPA and DHA. Biomass contributions towards growth were determined and the biochemical composition of the eggs was examined. In order to accurately determine ingestion rates, a method to account for microzooplankton grazing in particle removal experiments was developed. Balanced physiological budgets were compiled for C. finmarchicus in both seasons. The input terms of these budgets consisted of ingestion and the use of biomass, and the outputs were growth, respiration, excretion and egestion. Respiration and excretion were not determined experimentally, and were therefore determined by mass balance and compared to literature-derived values. In April, close agreement between literature- and mass balance-derived rates of respiration and excretion demonstrated that the experimentally determined components of the budget were accurate. Ingestion rates were low, and > 80 % of the C utilised was derived internally from somatic biomass. The absence of storage fatty acids and the low C:N ratio (~ 4 µg µg-1) of the biomass lost from the females indicated that these animals had been catabolising structural protein and were close to exhaustion. This suggests that when food is scarce, C. finmarchicus adopts a semelparous reproductive strategy. In July/August, the observed growth exceeded the estimated ingestion rates. This shortfall was possibly provided by cannibalising eggs. Assuming that EPA and DHA were used with high efficiency (0.9), the stoichiometric analysis predicted that these compounds were non-limiting in April. Using typical maximum growth efficiencies for C (< 0.6) and N (0.4), the former was predicted to be limiting because the biomass utilised was rich in N, EPA and DHA relative to the demand for C.