Lipid dynamics and feeding of dominant Antarctic calanoid copepods in the eastern Weddell Sea in December

Lipid content, fatty acid composition, and feeding activity of the dominant Antarctic copepods, Calanoides acutus, Calanus propinquus, and Metridia gerlachei, were studied at a quasi-permanent station in the eastern Weddell Sea in December 2003. During 3 weeks of the spring phytoplankton development, total lipid levels of females and copepodite stages V (CVs) of C. acutus were almost doubled. Meanwhile, only a slight increase in total lipid content occurred in M. gerlachei, and no clear trend was observed in lipids of C. propinquus females. The pronounced increase of lipids in C. acutus was due to an accumulation of wax esters. The proportion of wax esters in the lipids of M. gerlachei was clearly lower, while triacylglycerols played a more important role. In C. propinquus, triacylglycerols were the only neutral lipid class. There were no pronounced changes in the feeding activity of M. gerlachei, whereas the feeding activity of C. acutus had rapidly increased with the development of the phytoplankton bloom in December, which explains its rapid lipid accumulation. The combination of gut content and fatty acid trophic marker analyses showed that C. acutus was feeding predominantly on diatoms. The typical diatom fatty acid marker, 16:1(n-7), slightly decreased and the tracer for flagellates, 18:4(n-3), increased in females and CVs of C. acutus. This shift indicates the time, when the significance of flagellates started to increase. The three copepod species exhibited different patterns of lipid accumulation in relation to their trophic niches and different duration of their active phases. The investigations filled a crucial data gap in the seasonal lipid dynamics of dominant calanoid copepods in the Weddell Sea in December and support earlier hypotheses on their energetic adaptations and life cycle strategies.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Effects of the ice-edge bloom and season on the metabolism of copepods in the Weddell Sea,Antarctica

The metabolic responses of several species of Antarctic copepods to primary productivity and changes between seasons were investigated. To examine the influence of the spring ice-edge bloom on the metabolism of copepods, oxygen consumption rates were determined on specimens from three zones of widely different ice coverage and chlorophyll biomass: pack ice (pre-bloom), ice edge (bloom) and open water (post-bloom). Summer metabolic rates were compared with published winter rates. Field work was done in the Weddell Sea in the region of 60 °S, 36°W in late November and December 1993. Oxygen consumption rates were determined by placing individuals in syringe respirometers and monitoring the oxygen partial pressure for 10–20 hours. Higher metabolic rates were observed in the primarily herbivorous copepods, Calanoides acutus, Rhincalanus gigas and Calanus propinquus in regions of higher primary production: ice edge and open water. The carnivorous Paraeuchaeta antarctica showed a similar pattern. The omnivorous copepods Metridia gerlachei and Gaetanus tenuispinus showed no changes in metabolism between zones. Data on routine rates of copepods from the winter were available for C. propinquus and P. antarctica. In P. antarctica, rates were higher in the summer. Calanus propinquus showed a higher metabolic rate in the summer than in the winter, but the difference was not significant at the 0.05 level. It was concluded that copepods near the ice zone in the ice zone in the Antarctic rely on the spring ice-edge bloom for growth and completion of their life cycle.     

Build-up and decline of summer phytoplankton biomass in the eastern Weddell Sea,Antarctica

The seasonal development and decline of phytoplankton was investigated in the eastern Weddell Sea during summer and fall 1991. During the first half of the study (15 Jan–13 Feb) in an area off Vestkapp, favourable irradiance/mixing regimes initiated net phytoplankton growth in ice-free waters on the shelf and in stretches of open water over the partially ice-covered deep ocean. Chi a concentrations in the upper water column were moderate (0.2–0.8 g l^–1), but significantly above winter values. Later in the season (16 Feb–11 March), a phytoplankton bloom with surface Chl a concentrations ranging from 1.6–2.3 g l^–1 was encountered in an area further to the east. We suggest that the upper water column must have been stratified in this region for time scales of weeks to faciliate bloom development. Bacterial biomass and productivity generally paralleled the seasonal development of the phytoplankton. Nitrate concentrations in the upper mixed layer were substantially lower than would be expected from the existing phytoplankton standing stock, suggesting that heterotrophic consumption of organic matter by bacteria and zooplankton removed a large fraction of the primary production. The shallow seasonal pycnocline was eventually eroded by the passage of a storm, resulting in a homogeneous distribution of phytoplankton biomass over the entire water column, followed by sedimentation and deposition of phytodetritus on the sea floor. After the storm induced destratification, bacterial productivity was particularly high, amounting to more than half of the primary production (range: 10%–120%) in the upper water column. Subsequently, phytoplankton biomass in the upper water column decreased to values <1 g Chl a l^–1. The combination of low incident irradiances and incessant deep mixing prevented the phytoplankton biomass to increase again. During the last week of the investigation, extensive new-ice formation was observed. A major fraction of the residual surface plankton was incorporated into new sea ice, thus terminating the pelagic growth season of the phytoplankton in the eastern Weddell Sea.     

Spatio-temporal distribution and production of calanoid copepods in the central Baltic Sea

The aim of our study was the exploration of species-specificdistribution and production patterns of dominant copepods inthe Central Baltic Sea (Bornholm Basin). Spatio-temporal distribution,egg and secondary production were studied by means of net-samplingand egg production experiments from April to August 1999. Verticaland horizontal distribution patterns appeared to be linked witheach other and were primarily species-dependent. Both Acartiaspp. and Temora longicornis preferentially inhabited the upper30 m of the water column and the shallower marginal regionsof the Bornholm Basin. In contrast, the C4–5 and C6 ofPseudocalanus spp. preferentially inhabited the halocline region(50–70 m) and the deep central part of the area. Observeddifferences in horizontal distribution among these three copepodsappear to result from different depth preferences and depth-dependentwater circulation patterns. Egg production rates (EPR) clearlyexhibited seasonal differences with maximum EPR in May and minimumEPR in July. Mean EPR was significantly different between species,being highest in Acartia spp. and lowest in Pseudocalanus spp.The variability in EPR was related to differences in hydrographyand modelled food environment.     

Pelagic distribution and numbers of the Antarctic petrelThalassoica antarctica in the Weddell Sea during spring

Estimates of the population size of the Antarctic petrelThalassoica antarctica are hampered by its breeding locations in remote nunatak areas of the Antarctic continent. Studies at sea can provide additional information on numbers. Seabird censuses during spring 1992 showed few Antarctic petrels in the western part of the Weddell Sea, but high numbers east of the South Sandwich Islands. The vast majority of the birds occurred in a band of 300 km north to 150 km south of the outer ice edge. Numbers at sea fluctuated in agreement with synchronized colony attendance patterns in the pre-breeding phase and peaked shortly before egglaying when colonies are completely deserted. In this period, densities of Antarctic petrels in the marginal ice zone suggest that at least 2.7±0.5 million individuals occur in the Weddell Sea. It is likely that similar numbers occur immediately east of the study area. The distribution of the petrels matches the location, but not the size, of known breeding colonies in Dronning Maud Land and Coats Land, which suggests that important colonies in this area remain to be discovered. The observations imply that Antarctic petrels in the Weddell Sea commute over ice a surprisingly large distance of at least 2,000 km for a single pre-breeding visit to the colonies.     

Gut contents and diel feeding rhythm in dominant copepods in the ice-covered Weddell Sea,March 1992

Zooplankton was sampled at a diurnal station during the drift of the Ice Station Weddell-1 in the western Weddell Sea in March 1992. Gut contents of Metridia gerlachei, Calanoides acutus, Calanus propinquus and Rhincalanus gigas were studied. Calanoides acutus was trophically inactive, but 18%, 33% and 45% of Calanus propinquus, R. gigas and M. gerlachei, respectively, contained food in their guts. Diel changes in gut levels and percentage of individuals with full guts with maximum during the dark period were observed in M. gerlachei copepodite stage V and females. The possible reasons for observed differences in foraging patterns of the four copepod species are discussed.     

Dynamics in bacterial surface properties of a natural bacterial community in the coastal North Sea during a spring phytoplankton bloom

The hydrophilic and hydrophobic properties of single cells of natural bacterioplankton communities were determined using a recently developed staining method combined with confocal laser scanning microscopy and advanced image analysis. On an average, about 50% of the bacterial cell area was covered by hydrophobic and only 16% by hydrophilic properties, while about 72% was covered by the genome. However, the size of these properties was independent of the bacterial cell size. Bacterial hydrophobicity was positively correlated with ambient NH(4)(+) concentrations and negatively correlated with overall bacterial abundance. The expression of hydrophilicity was more dynamic. Over the spring phytoplankton bloom, the bacterioplankton ratio(phil/phob) repeatedly reached highest values shortly before peaks in bacterioplankton abundance were observed, indicating a direct and fast response of bacterial surface properties, especially hydrophilicity, to changing environmental conditions. Compared to bacterial strains, recently studied with the same method, cells of marine bacterioplankton communities are much smaller and less frequently covered by hydrophobic or hydrophilic properties. While the percentage area covered by the genome is essentially the same, the percentage area covered by hydrophobic or hydrophilic properties is much smaller.     

Nitrogen uptake in the Weddell Sea during late winter and spring

Summary Uptake rates of ammonium, nitrate and urea were measured during the EPOS leg 1 cruise to the Weddell Sea in October–November 1988 using the isotope ¹⁵N. Nitrate was the most important nitrogen source both for ice algae (f-ratio 0.88) and for phytoplankton in the water column (f-ratio 0.85). Indications of a gradual decrease in % new production with time were found in the outer marginal ice zone. Nitrogen uptake rates in ice algae from the sub-ice assemblage were light-limited at in situ irradiances. Significant regeneration of ammonium was found in ice algal samples only.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Distribution and abundance of micronekton and macrozooplankton in the NW Weddell Sea: relation to a spring ice-edge bloom

Micronekton and macrozooplankton were collected during the austral spring of 1993 in the NW Weddell Sea. Sampling was done in three areas of the marginal ice zone: pack ice, ice edge, and open water, to examine the short-term effects of the spring phytoplankton bloom on the distribution and abundance of dominant fish and invertebrate species. Significant differences were observed for several common species, including Salpa thompsoni,Euphausia superba, Electrona antarctica, Gymnoscopelus braueri,and G. opisthopterus. Increased abundance seaward of the pack ice for these species is attributed to elevated phytoplankton and zooplankton biomass at the ice edge and in the open water areas. Distribution of the hyperiid amphipods, Cyllopus lucasii and Vibilia stebbingi mirrored that of S. thompsoni. No distributional trends between the areas were observed for Thysanoessa macrura, the amphipods Cyphocaris richardi and Primno macropa, the decapod shrimp Pasiphaea scotiae, the scyphomedusae Atolla wyvilli and Periphylla periphylla, and chaetognaths, indicating a trophic independence from the ice-edge bloom for these species. Lower occurrence of the mesopelagic fish Bathylagus antarcticus and Cyclothone microdon under the ice suggested that trophic repercussions of the spring bloom can also extend to deeper living species.     

Potential impact of the main benthic amphipods on the eastern Weddell Sea shelf ecosystem (Antarctica)

As they represent one of the most diversified taxonomic groups on Antarctic bottoms, amphipods are likely to play a complex role in biogeochemical fluxes that occur within benthic ecosystems. The aim of this paper is to present, using both digestive tract analyses and relative species abundance data, the impact of amphipod feeding on different potential preys of the Weddell Sea. The study is based on data obtained for 29 representative amphipod species collected at 130 stations distributed along the eastern shelf of the Weddell Sea (depth range: 60-2,000 m) during three summer cruises, from 1989 to 1998. Sedimenting plankton particles (10-27%), crustaceans (22-32%) and fish carrion (5-18%) are the main food resources. Other abundant potential preys, such as molluscs or tunicates, do not seem to be consumed. Variations in the proportions of the different preyed food items are observed, mainly related to differences in relative amphipod species composition in samples. Presented results will help in refining ecological models of the prospected area, but also underline the need for accurate and reliable measurements of the feeding rates of Antarctic benthic organisms.     

A small population of planktonic Flavobacteria with disproportionally high growth during the spring phytoplankton bloom in a prealpine lake

Bacterioplankton growth in temperate Lake Zurich (Switzerland) was studied during the spring phytoplankton bloom by in situ techniques and short-term dilution bioassays. A peak of chlorophyll a (Chl a ) concentrations was followed by a rise of bacterial cell numbers and leucine assimilation rates, of the proportions of cells incorporating 5-bromo-2-deoxyuridine (BrdU), and of community net growth rates in dilution cultures. Incorporation of BrdU was low in Betaproteobacteria (2 ± 1%), indicating that these bacteria did not incorporate the tracer. Pronounced growth of Betaproteobacteria in the enrichments was only observed after the decline of the phytoplankton bloom. An initial peak in the proportions of BrdU-positive Actinobacteria (30%) preceded a distinct rise of their cell numbers during the period of the Chl a maximum. Cytophaga–Flavobacteria (CF) changed little in numbers, but featured high proportions of BrdU-positive cells (28 ± 12%). Moreover, CF represented > 90% of all newly formed cells in dilution cultures before and during the phytoplankton bloom. One phylogenetic lineage of cultivable Flavobacteria (FLAV2) represented a small (0.5–1%) but highly active population in lake plankton. The growth rates of FLAV2 in dilution cultures doubled during the period of the Chl a maximum, indicating stimulation by phytoplankton exudates. Thus, CF, and specifically Flavobacteria , appeared to be substantially more important for carbon transfer in Lake Zurich spring bacterioplankton than was suggested by their standing stocks. The high in situ growth potential of these bacteria might have been counterbalanced by top-down control.     

Comparison of phosphorus deficiency indices during a spring phytoplankton bloom in a eutrophic reservoir

1. Phosphorus limitation was studied along the eutrophic, canyon-type ?ímov reservoir (Czech Republic) during a spring phytoplankton bloom. Concentration of soluble reactive phosphorus (SRP), C:P molar ratio in seston, extracellular alkaline phosphatase activity (APA), and P limitation (bioassay) were used as indices for phosphorus deficiency in the phytoplankton. 2. SRP, C:P, APA, and P limitation indicated a moderate P deficiency in the downstream, but not upper, part of the reservoir. 3. Significant correlations between these parameters were found in the downstream part. Chlorophyll a concentration correlated with APA and P limitation in the upper part. 4. APA was significantly enhanced in the phosphorus-deficient phytoplankton. However, APA was apparently not related to total biomass or species composition of the phytoplankton. 5. Generally, APA was closely correlated with pH in the reservoir. However, extracellular alkaline phosphatases, with a pH optimum above 9.0, were induced and active only during the phytoplankton bloom, whereas low background activity of extracellular phosphatases was found at low chlorophyll a concentrations (winter, clear-water phase).     

Shrimp (Decapoda,Natantia) occurrence and distribution in the eastern Weddell Sea,Antarctica

Summary 108 successful ground and Agassiz trawl catches were taken between 155 and 2031 m depth in the eastern Weddell Sea on board RV Polarstern in spring and summer (October–February) 1985–1989. In addition, 7 hauls were taken with a semipelagic trawl. Only 19 hauls (16.5%) contained no shrimps. The others yielded large numbers of Notocrangon antarcticus, Chorismus antarcticus, and Nematocarcinus lanceopes as well as 20 Lebbeus antarcticus and 11 specimens of an Eualus species new to science. 8 Pasiphaea scotiae were caught in a pelagic krill trawl. No reptant decapod crustaceans were detected in the study area. Shrimp densities determined from trawl catches were lower than estimates derived from underwater photography but in the same order of magnitude. Although yields of the three common shrimp species in some cases exceeded 20 kg per 0.5 h haul, shrimp stocks in the area cannot be considered to be of commercial significance. A wider geographical distribution and greater frequency of shrimps in high Antarctic waters was found than described hitherto. There was considerable variation in numbers, sex composition, occurrence at different depths, and size-frequency distributions. C. antarcticus and N. antarcticus grow to a larger size compared with individuals from the Antarctic Peninsula area. Within the area of investigation, length frequency distributions are skewed towards larger sizes at higher latitudes. In the eastern Weddell Sea larger specimens of the three common species live at greater depths than smaller individuals. Potential reasons for these differences are discussed.AWI Publication No. 124     

On processes determining the vertical stability of surface waters in the marginal ice zone of the north-western Weddell Sea and their relationship with phytoplankton bloom development

Summary Ice-edge-related phytoplankton blooms following the retreating sea-ice in the marginal ice zone are frequently observed phenomena. Such blooms are generally short-lived and are followed by a strong decrease in the chlorophyll concentration towards the open ocean, generally explained by the degradation of the vertical stability. Solar heating and ice melting, which control the stability of the surface water of the north-western Weddell Sea during sea-ice retreat in spring were analysed in order to relate the spatial features of the phytoplankton ice-edge bloom in 1988 to the density field. Solar heating has little effect on the density of seawater in ice-covered areas because the thermal expansion coefficient is very low close to the freezing temperature. Outside the marginal ice zone, the temperature effect on stratification increases and the combined contribution of melting and heating on buoyancy input to the surface layer is roughly constant. As a consequence, the low phytoplankton stocks in the open ocean adjacent to the marginal ice zone, after an initial bloom peak following the retreating ice in spring, are not necessarily caused by deep turbulent mixing, in contrast to what is often assumed.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Influence of sea ice on the composition of the spring phytoplankton bloom in the northern Baltic Sea

During the late winter and spring of 1994, the influence of sea ice on phytoplankton succession in the water was studied at a coastal station in the northern Baltic Sea. Ice cores were taken together with water samples from the underlying water and analysed for algal composition, chlorophyll a and nutrients. Sediment traps were placed under the ice and near the bottom, and the sedimented material was analysed for algal composition. The highest concentration of ice algae (4.1 mmol C m⁻²) was found shortly before ice break-up in the middle of April, coincidental with the onset of an under-ice phytoplankton bloom. The ice algae were dominated by the diatoms Chaetoceros wighamii Brightwell, Melosira arctica (Ehrenberg) Dickie and Nitzschia frigida Grunow. Under the ice the diatom Achnanthes taeniata Grunow and the dinoflagellate Peridiniella catenata (Levander) Balech were dominant. Calculations of sinking rates and residence times of the dominant ice algal species in the photic water column indicated that only one ice algal species (Chaetoceros wighamii) had a seeding effect on the water column: this diatom dominated the spring phytoplankton bloom in the water together with Achnanthes taeniata and Peridiniella catenata. Received: 9 May 1997 / Accepted: 15 February 1998     

Preliminary investigation of the contribution of fast-ice algae to the spring phytoplankton bloom in Ellis Fjord,eastern Antarctica

 Algae released from fast-ice in Ellis Fjord, eastern Antarctica, made little contribution to subsequent phytoplankton growth. Dominant taxa in the interior ice community included Nitzschia cylindrus (Grun) Hasle, Navicula glaciei V.H. and a dinoflagellate cyst. Diatom mortality within the ice was high. The algal contribution to the phytoplankton from the fast ice was estimated by calculating the difference between algal biomass in ice cores taken on 14 November with those taken on 18 December 1992. The biomass of sedimenting phytoplankton was estimated using sediment traps; weekly cell counts of water were used to monitor net phytoplankton growth. The low contribution from the fast-ice of Ellis Fjord to the phytoplankton is similar to results from other Antarctic fast-ice communities but is not necessarily reflective of processes occurring within either Antarctic or Arctic pack ice communities. An algal mat growing on the base of the fast-ice had a carbon standing crop of between 0.231 gC m^-2 and 0.022 gC m^-2. Much of this was delivered to the water column as the ice melted while the remainder was exported. Received: 15 March 1995/Accepted: 4 September 1995     

A study on octopodids from the eastern Weddell Sea, Antarctica

A comprehensive study of octopodids in the Weddell Sea was conducted during cruise ANT XIII/3 of RV "Polarstern". The study yielded eight species of incirrate octopodids, three of which were undescribed. There appeared to be no differences in octopodid species assemblage in the two sampling areas (Kapp Norvegia and south of Drescher Inlet), supporting the theory that there is a single macrobenthic assemblage on the eastern shelf of the Weddell Sea. Six of the octopodid species belonged to the genus Pareledone, illustrating the extensive radiation of this endemic genus within the Southern Ocean. The fragmented nature of suitable habitats and disturbance caused by glaciation cycles are proposed as mechanisms for this radiation. Comparative data illustrate that both the number of octopodid species present and their abundance are greater at higher latitudes than close to the Antarctic Polar Frontal Zone.     

Vertical distribution and cyst production of Peridiniella catenata (Dinophyceae) during a spring bloom in the Baltic Sea

Vertical distribution and cyst production of the chain-forming,spring dinoflagellate Peridiniella catenata were studied throughoutthe spring season of 2000 in the coastal Gulf of Finland. Numbersof cells were monitored in the water column, and cyst sedimentationwas recorded using multiple sediment traps moored at three discretedepths. At the onset of the spring bloom, most of the populationwas situated in the euphotic zone. When the bloom progressed,the population was more evenly dispersed throughout the watercolumn. Coinciding with the decline of the spring bloom, afternitrogen depletion, a general reduction of cell size of P. catenataand a break-up of chains were observed. Resting cysts startedto appear shortly after the peak of the bloom, in sedimentationtraps moored at 30 and 40 m depth. Cysts were only retrievedfrom the uppermost sediment trap on three of the six samplingoccasions, constituting only a small proportion of all cystsproduced by P. catenata during spring. Our results suggest thatcyst production of this vertically migrating organism takesplace to a large extent in deep water layers and emphasizesthe necessity of whole water column monitoring in studies aimingto understand in situ life-cycle transformations of verticallymigrating dinoflagellates.