Distribution of antarctic zooplankton around Elephant Island during the austral summers of 1988, 1989, and 1990

Year to year variation and vertical distributions of epipelagic Zooplankton around Elephant Island and King George Island were examined with samples collected with bongo nets and a 1 m² MOCNESS during the austral summers (Jan–Feb.) of 1988, 1989 and 1990. Copepods were the major components of epipelagic Zooplankton (in numbers) with dominance of Metridia gerlachei (1988 and 1989) and small calanoids and cyclopoids (1990). Euphausiids and salps were the next most abundant groups. The percent composition of euphausiids decreased from 1988 to 1990 while that of salps increased. The abundance of salps exceeded euphausiids and major taxa of copepods in 1990. Local patches of polychaetes and amphipods were also found. Statistically significant annual variations with increased numbers in 1990 were found by analyses of variance in total abundance, abundances of copepods, salps, chaetognaths and amphipods, but abundances of euphausiids, polychaetes and fishes showed no significant annual variations. When the study area was divided geographically, horizontal variability in abundance within each year showed no significance in total abundance, abundances of copepods, euphausiids, amphipods and fishes, but significance in salps, polychaetes and chaetognaths. Results of site clustering based on covariances of abundances of eleven major taxa were well matched, though not perfect, with the distribution of surface water temperatures which could be used as a tracer of source water masses suggesting that spatial variation was related to hydrodynamic conditions. Factor analyses showed that annual and spatial variations in abundance were mainly caused by only two taxa, Metridia gerlachei and salps (mostly Salpa thompsoni). These two taxa were responsible for about 60% and 30% of total variance, respectively, and were useful indicators of the interannual variation. That is, 1988 and 1989 were the years of M. gerlachei, and 1990 was the year of salps. From vertically stratified MOCNESS samples, it was shown that the major taxa in this study area were active vertical migrators. While most samples obtained by relatively shallow tows (uppermost 100 m depth) were composed of exclusively one or two taxa, those from relatively deep tows (down to 200 m) showed various patterns of vertical stratification suggesting that the patterns of vertical migration were species specific. Species specific ontogenetic vertical migration associated with elevated habitat temperatures also seemed to be responsible for the annual variation in zooplankton distribution in the upper water column.     

Biomass and metabolism of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral spring

Zooplankton biomass (as dry weight), respiration and ammonia excretion were studied in three different size classes (200–500, 500–1000 and >1000 μm) in the Bransfield Strait during December 1991. Average mesozooplankton biomass was 86.45 ± 56.74 mg · dry weight · m⁻², which is in the lower range of the values cited in the literature for polar waters. Higher biomass was observed in the Weddell water. The small size fraction accounted for about 50% of total biomass while the largest one represented 35%. Rather high metabolic rates were found, irrespective of whether the organisms were incubated in the presence of food. No significant differences were observed in mass specific respiration and ammonia excretion rates between different temperatures of incubation (0.2–2.3°C) and between the size classes studied. Because of the very low biomass values observed, the metabolic requirements of mesozooplankton during December represented a small fraction of the primary production. Accepted: 5 September 1998     

Distribution of six major copepod species around South Georgia during an austral winter

Summary A net sampling survey was conducted around the island of South Georgia during July/August 1983. This study compares the age structure and vertical and horizontal distributions of the dominant copepods Calanoides acutus, Calanus simillimus, C. propinquus, Rhincalanus gigas, Metridia lucens and M. gerlachei. The chief physical and biological factors affecting the distributions of these species are assessed and the results are compared with those from a similar survey around the island carried out in early summer (1981/1982). The survey grid lay within the Polar Front during the winter survey, and horizontal changes in copepod abundance corresponded well to the temperature gradient across the front. This pattern was interrupted by the South Georgia shelf where the seasonal migrants (Calanoides acutus, Rhincalanus gigas and Calanus simillimus) occurred in high abundance. The concentration of these migrants over the shelf relative to the oceanic surface layer was attributed to the shelf having prevented their seasonal migration. Within the oceanic area the copepods occupied differing depths, with Calanoides acutus and Metridia gerlachei living deeper than Calanus simillimus, C. propinquus and M. lucens. The populations also tended to live deeper in the warmer (NW) portion of the oceanic survey area. In contrast to the summer survey the age structure of each species showed little variation throughout the survey area. This was attributed mainly to the decreased rates of copepod growth and metabolism in winter.     

Unexpected weight gain in resident Antarctic Terns Sterna vittata during the austral winter

Antarctic Terns Sterna vittata (Fig. 1) may display two very different migratory behaviours. According to Cooper (1976), the terns breeding on Tristan da Cunha in the South Atlantic fly thousands of kilometers to the coasts of Africa where they moult. Antarctic Terns that inhabit the more southern and colder Antarctic Peninsula region moult on their breeding grounds. An early account of these seemingly resident peninsular terns (Holdgate 1963) leaves little doubt that at least part of the tern population wintered in the vicinity of Arthur Harbor (64°46'S 64°03'W), Anvers Island, west of the Antarctic Peninsula. Watson (1975) stated that adult Antarctic Terns are generally sedentary around many insular breeding stations, moving only to the nearest open water in winter. During the years 1975 through 1978, 19 tern specimens of different sexes and ages were collected at Arthur Harbor in the non-breeding season near U.S. Palmer Station. An additional eight terns were collected at sea a short distance from Anvers Island during the non-breeding season in 1985 (Pietz & Strong, in press). I found that the adult birds taken at the height of winter weighed significantly more than the 150–180 g of a normal breeding Antarctic Tern. This unexpected discovery prompted me to examine the weights of an additional 34 specimens that had been collected at or near Anvers Island during several breeding seasons. By comparing the weights of adult terns by sex, age, and collection date (Fig. 2, Table 1) I found that both males and females weighed significantly more in the winter non-breeding season (April-September) than in the summer breeding season (October-March) (t₂₄ = 6·57, P < 0·001, and t₁₆ = 5·71, P < 0·001, respectively). No significant differences were detected between male and female weights in summer (t₂₃ = 0·76, P > 0·20) or winter (t₁₇ = 1·16, P > 0·20). In short, it appears that body-weights of adult terns rise rather dramatically following breeding, attain a peak in mid-winter, and then fall at the approach of the next breeding season (Fig. 2). I suggest that this increased body-weight is an adaptation to the austral winter rather than simply a recovery from weight loss due to energetic costs of breeding and moulting.     

Unexpected weight gain in resident Antarctic Terns Sterna vittata during the austral winter

Antarctic Terns Sterna oittata (Fig. 1) may display two very different migratory behaviours. According to Cooper (1976), the terns breeding on Tristan da Cunha in the South Atlantic fly thousands of kilometers to the coasts of Africa where they moult. Antarctic Terns that inhabit the more southern and colder Antarctic Peninsula region moult on their breeding grounds. An early account of these seemingly resident peninsular terns (Holdgate 1963) leaves little doubt that at least part of the tern population wintered in the vicinity of Arthur Harbor (64°46′S 64°03′W), Anvers Island, west of the Antarctic Peninsula. Watson (1975) stated that adult Antarctic Terns are generally sedentary around many insular breeding stations, moving only to the nearest open water in winter. During the year 1975 through 1978, 19 tern specimens of different sexes and ages were collected at Arthur Harbor in the non-breeding season near U.S. Palmer Station. An additional eight terns were collected at a sea short distance from Anvers Island during the non-breeding season in 1985 (Pietz & Strong, in press). I found that the adult birds taken at the height of winter weighed significantly more than the 150-180g of a normal breeding Antarctic Tern. This unexpected discovery prompted me to examine the weights of an additional 34 specimens that had been collected at or near Anvers Island during several breeding seasons. By comparing the weights of adult terns by sex, age, and collection date (Fig. 2, Table 1) I found that both males and females weighed significantly more in the winter non-breeding season (April-September) than in the summer breeding season (October-March) (t₂₄= 6.57, P < 0.001, and t₁₆= 5.71, P < 0.001, respectively). No significant differences were detected between male and female weights in summer(t₂₃=0.76, P >0.20) or winter (t₁₇=1.16, P0.20). In short, it appears that body-weights of adult terns rise rather dramatically following breeding, attain a peak in mid-winter, and then fall at the approach of the next breeding season (Fig. 2). I suggest that this increased body-weight is an adaptation to the austral winter rather than simply a recovery from weight loss due to energetic costs of breeding and moulting.     

Benthic algae support zooplankton growth during winter in a clear-water lake

We used stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ¹³C values of calanoid ( Eudiaptomus graciloides ) and cyclopoid ( Cyclops scutifer ) zooplankton in autumn suggest a food resource of pelagic origin during the ice-free period. The zooplankton δ¹³C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ¹³C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ¹³C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ¹⁵N of the C. scutifer food resource during winter was low compared to δ¹⁵N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via ¹⁵N-depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi-chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.     

Metabolic recovery of continental antarctic cryptogams after winter

The activation of metabolism after the winter period was investigated in several mosses and lichens in continental Antarctica. Thalli that were still in their over-wintering inactive state in early spring were sprayed artificially and the time-dependent activation of photosystem II (PSII), carbon fixation and respiration was determined using gas exchange and chlorophyll a fluorescence techniques. The investigated lichens recovered PSII activity almost completely within the first few minutes and gross photosynthesis was fully reactivated within a few hours. In contrast, photosynthesis took much longer to recover in mosses, which could indicate a general difference between the green-algal symbionts in lichens and moss chloroplasts. Only small and quickly reversible increased rates of respiration were observed for the foliose lichen Umbilicaria aprina from a more xeric habitat. In contrast, species occurring near persistent meltwater, such as the moss Bryum subrotundifolium and the lichen Physcia caesia, had highly increased respiration rates that were maintained for several days after activation. Calculation of the carbon balances indicated that the activation pattern strongly dictated the length of time before a carbon gain was achieved. It appears that the differences in recovery reflect the water relations of the main growth period in summer.     

Biomass and potential feeding, respiration and growth of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral summer

Biomass (as dry weight and protein content), gut fluorescence, electron transfer system (ETS) and aspartate transcarbamylase (ATC) activities were studied in different size fractions (200–500, 500–1000 μm and 1–14 mm) in the Bransfield Strait (Antarctic Peninsula) during January 1993. Very low values of zooplankton biomass were observed in all the size classes studied. About 56% of total biomass was due to the large size fraction (1–14 mm) while the smallest one (200–500 μm) accounted for about 26%. Gut fluorescence values increased in relation to the size class considered, as expected, being the differences from the smaller to the highest size fractions of orders of magnitude. Calculated ingestion rates showed that about 60–80% of total zooplankton ingestion (<14 mm) was due to the smaller organisms. Higher average values and higher variability of specific ETS activity was observed in the smaller size fraction while no differences between size classes were observed for the specific ATC activity. Biomass, gut fluorescence, ETS and ATC activities were not significantly different between the Bellingshausen and Weddell waters, although higher standard deviation was normally found at the former area. With the restrictions of using the above indices to estimate physiological rates, potential grazing of mesozooplankton (<14 mm) accounted for a rather low portion (<10%) of the primary production. The index of growth showed high values, suggesting no food limitation of mesozooplankton. Therefore, other processes such as predation should account for the very low biomass found and for the fate of a large portion of primary production. Accepted: 26 March 2000     

Distribution and abundance of seabirds and fur seals near the Antarctic Peninsula during the austral winter, 1986

Twenty one species of seabirds plus fur seals were observed at sea near the Antarctic Peninsula, between 60 °–68 °S, in May and June 1986, a season for which few published observations of marine animals are available for this area. Here we describe and quantify the importance of fishing activities as well as sea-ice cover and other environmental variables to the distribution patterns of birds and seals. The most striking aspect of the winter avifauna was its pronounced concentration near fishing trawlers operating on the continental shelf to the north and west of Elephant Island, and its temporal shift in response to the seasonal advance of the ice edge.     

Phytoplankton composition in the Weddell-Scotia Confluence area during austral spring in relation to hydrography

During the EPOS leg 2 cruise of the RV Polarstern, carried out in late austral spring of 1988–1989, the composition of phytoplankton in relation to the distribution of hydrographic parameters was studied in four successive transects carried out along 49°W and 47°W, across the Weddell-Scotia Confluence (WSC) and the marginal ice zone (which overlapped in part). In all transects, a maximum of phytoplankton biomass was found in the WSC, in surface waters stabilized by ice melting. Different phytoplankton assemblages could be distinguished. North of the Scotia Front (the northern limit of the WSC) diatoms with Chaetoceros neglectus, Nitzschia spp. and (Thalassiosira gravida) dominated the phytoplankton community. This assemblage appeared to have seeded a biomass maximum which occupied, during the first transect, an area of the WSC, south of the Scotia Front. The southernmost stations of the first transect and all the stations to the south of the Scotia Front in the other transects were populated by a flagellate assemblage (with a cryptomonad, Pyramimonas spp. and Phaeocystis sp.) and an assemblage of diatoms (Corethron criophilum and Tropidoneis vanheurkii among others) associated to the presence of ice. During the last three transects, the flagellate assemblage formed a bloom in the low salinity surface layers of the WSC zone. The bulk of the biomass maximum was formed by the cryptomonad which reached concentrations up to 4×10⁶ cells l^–1 towards the end of the cruise. Multivariate analysis is used to summarize phytoplankton composition variation. The relationships between the distribution of the different assemblages and the hydrographic conditions indicate that the change of dominance from diatoms to flagellates in the WSC zone was related to the presence of water masses from different origin.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Feeding of dominant zooplankton in Prydz Bay, Antarctica, during austral spring/summer: food availability and species responses

Information on the food and predation of zooplankton species is essential for an improved understanding of zooplankton community dynamics of the Southern Ocean. Feeding of dominant zooplankton species at locations across the neritic, slope and oceanic regions of Prydz Bay, Antarctica, was investigated with incubation experiments during austral spring/summer of 2009/2010 to identify the response of dominant copepods and krill to different feeding environments. Results showed distinct spatial and temporal variations in ingestion and filtration of predominant copepods and krill. In late spring, Calanoides acutus was inactive and the ingestion rate was only 1.30 μgC/ind/day. During early summer, a diatom bloom was in progress at station IS21, showing a peak biomass of Thalassiosira spp. and Fragilaria spp. Daily ingestion rates of Euphausia crystallorophias, C. acutus, Metridia gerlachei and Ctenocalanus citer were relatively high. By contrast, copepod ate predominantly ciliates in slope and oceanic regions where microplankton biomass were lower (<20 μgC/L). During late summer, microplankton of neritic regions, mainly composed of nano-sized Pseudo-nitzschia spp. and ciliates, was less than 10 μgC/L. C. acutus incubated in neritic regions mainly ate ciliates. The total microplankton biomass was lower (<5 μgC/L) and predominated by Pseudo-nitzschia spp. in slope regions north of Fram Bank, and daily ingestion rates of incubated copepods were less than 2.5 μgC/ind. Our results clearly demonstrated that copepods and krill had flexible feeding strategies to cope with temporally and spatially changing food availability in Prydz Bay. Meanwhile, ciliates appeared to represent an important carbon source for zooplankton, especially in regions with lower food concentrations.     

Protist community composition in the Pacific sector of the Southern Ocean during austral summer 2010

Knowledge about the protist diversity of the Pacific sector of the Southern Ocean is scarce. We tested the hypothesis that distinct protist community assemblages characterize large-scale water masses. Therefore, we determined the composition and biogeography of late summer protist assemblages along a transect from the coast of New Zealand to the eastern Ross Sea. We used state of the art molecular approaches, such as automated ribosomal intergenic spacer analysis and 454-pyrosequencing, combined with high-performance liquid chromatography pigment analysis to study the protist assemblage. We found distinct biogeographic patterns defined by the environmental conditions in the particular region. Different water masses harbored different microbial communities. In contrast to the Arctic Ocean, picoeukaryotes had minor importance throughout the investigated transect and showed very low contribution south of the Polar Front. Dinoflagellates, Syndiniales, and small stramenopiles were dominating the sequence assemblage in the Subantarctic Zone, whereas the relative abundance of diatoms increased southwards, in the Polar Frontal Zone and Antarctic Zone. South of the Polar Front, most sequences belonged to haptophytes. This study delivers a comprehensive and taxon detailed overview of the protist composition in the investigated area during the austral summer 2010.     

Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter

1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, however, known about the role of fish during winter. 2. We analysed data from 34 lakes studied for 8–9 years divided into three seasons: summer, autumn/spring and winter, and four lake classes: all lakes, shallow lakes without submerged plants, shallow lakes with submerged plants and deep lakes. We recorded how body weight of Daphnia and then cladocerans varied among the three seasons. For all lake types there was a significant positive correlation in the mean body weight of Daphnia and all cladocerans between the different seasons, and only in lakes with macrophytes did the slope differ significantly from one (winter versus summer for Daphnia). 3. These results suggest that the fish predation pressure during autumn/spring and winter is as high as during summer, and maybe even higher during winter in macrophyte‐rich lakes. It could be argued that the winter zooplankton community structure resembles that of the summer community because of low specimen turnover during winter mediated by low fecundity, which, in turn, reflects food shortage, low temperatures and low winter hatching from resting eggs. However, we found frequent major changes in mean body weight of Daphnia and cladocerans in three fish‐biomanipulated lakes during the winter season. 4. The seasonal pattern of zooplankton : phytoplankton biomass ratio showed no correlation between summer and winter for shallow lakes with abundant vegetation or for deep lakes. For the shallow lakes, the ratio was substantially higher during summer than in winter and autumn/spring, suggesting a higher zooplankton grazing potential during summer, while the ratio was often higher in winter in deep lakes. Direct and indirect effects of macrophytes, and internal P loading and mixing, all varying over the season, might weaken the fish signal on this ratio. 5. Overall, our data indicate that release of fish predation may have strong cascading effects on zooplankton grazing on phytoplankton and water clarity in temperate, coastal situated eutrophic lakes, not only during summer but also during winter.     

Patchiness and composition of coral reef demersal zooplankton

Zooplankton samples were collected weekly for a full year withdemersal traps on a coral reef off the west coast of Barbados.There was a marked temporal variability in weekly catches bothin terms of abundance and biomass. Patchiness occurred at allsampling frequencies from 2 to 26 weeks, but spectral analysisindicated a variance shift at a frequency of 8–10 weeksAggregations of the two most abundant taxa, the copepoditesand the microzooplankton, occurred at 8–12 week intervalsand significant differences in abundance and biomass were foundbetween mean bimonthly zooplankton catches Lagged cross-correlationsat 7 and 11 weeks between chlorophyll and microzooplankton andcopepodites suggest that aggregations are connected to cyclesof primary production. There was a negative correlation betweenzooplankton abundance and surface water salinity in 8 of 16taxa Copepods were the most abundant taxon overall. Microzooplanktonand copepodites comprised 96% of the abundance and 66% of thebiomass Decreases in taxonomic richness and in diversity wereassociated with patchiness of small-sized copepodites and microzooplankton,suggesting that composition was altered and stability temporarilylessened during peaks of abundance     

Biogeographical structure of the microphytoplankton assemblages in the region of the Subtropical Convergence and across a warm-core eddy during austral winter

The distribution of rnicrophytoplankton in the region of theSubtropical Convergence (STC) and across a warm-core eddy shedfrom the Aguihas Return Current was investigated along two transectsin late austra] winter (June-July) 1993, during the South AfricanAntarctic Marine Eco system Study (SAAMES) III cruise. Samplingwas undertaken for the analysis of nutrients, and for the enumerationand identification of microphytoplankton species. Along bothtransects, chlorophyll con centrations were highest at stationsat the southern boundary of the STC and at the periphery ofthe warm-core eddy. Of the variance associated with chlorophyllconcentration, temperature accounted for 65% of the total. Alongboth transects, a decrease in species richness from north tosouth was observed. The spatial distribution of the numericallydominant diatom species was similar in both tran sects. Themicrophytoplankton assemblage was dominated by the subtropicaldiatom species Chaetoceros constnctus north of the STC, andby Pseudoeunotia doliolus within the eddy and south of the STC.Using cluster and ordination analyses, three significantly differentgroupings of stations were identified along the combined transects.These coincided with stations located north and south of theSTC and with the warm-core eddy proper, confirming that theSTC represents a strong biogeograph ical boundary. The predominanceof the warm-water species P.doliolus and Planktoniella sol inand around the warm-core eddy south of the STC suggests thateddies are important in the transfer of microphytoplankton acrossthis strong biogeographical boundary.     

Changes in the composition of winter rape oil during seed maturation

The course of biosynthesis of fatty acids in the seeds of winter rape (Brassica napus L. ssp.oleifera, f.biennis cv. T?ebí?ská) was investigated. After the termination of flowering seed samples were taken at five intervals, the seeds were divided into 4 fractions according to size, and their weight, water content, oil content and fatty acid composition were determined. The oil content was found to increase in all size categories with time, with the exception of a minute drop when complete maturity is reached. Larger seeds contained more oil. The fatty acid composition changes with time in the individual size fractions almost continuously. The same holds for differences between seed sizes of the same sample. The main change in oil composition consists in the decrease of C₁₈ acids in favour of C₂₂ acids. Greatest decrements during maturation were found with oleic acid, less with linoleic acid. In absolute amounts the quantity of all synthesized acids rises, the greatest rise being observed with C₂₂ acids (i.e. predominantly erucic acid). It follows from the mean rates of synthesis of the individual groups (C₁₆, C₁₈, C₂₀, C₂₂) of fatty acids that the fraction of C₂₂ rate of synthesis increases, while that of the C₁₈ acids decreases with the same speed. The results indicate that the fatty acid synthesis is most intense during the second half of seed maturation, the main role being played by accelerating the synthesis of higher acids, especially of erucic acid.     

Changes in fatty acid composition of winter wheat during frost hardening

Twelve day old winter wheat seedlings (cvs Kharkov, frost hardy and Champlein, less hardy) accumulated linolenic acid at the expense of linoleic acid during controlled hardening. The change was most pronounced in the roots, where it was not specific to the phospholipid fraction. It was less marked in the leaves, but occurred there mainly in the phospholipids. The lack of differences between fatty acid profiles of the two cultivars rules out the explanation of varietal differences in frost hardiness in winter wheat on the basis of major changes in fatty acid unsaturation.     

Species diversity, spatial distribution, and assemblages of zooplankton within the Strait of Magellan in austral summer

The main aim of this work was to identify zooplankton assemblages by means of statistical testing and associate them with hydrographic properties of the Strait of Magellan and its microbasins. Zooplankton samples were collected by the R/V Cariboo in late austral summer 1991. Nineteen stations were sampled by BIONESS from the surface layer to 900 m depth, along the main longitudinal axis of the Strait of Magellan. There was a marked regional-scale pattern in zooplankton species diversity and richness, related to the hydrographical features of the Strait and its sub-basins. Six groups of samples were identified by cluster analysis in terms of zooplankton structure, and related to sea-water properties of temperature, salinity, and Chl a (Sperman’s correlation coefficient). Plankton assemblages of the Strait of Magellan seem closely linked to the remote sub-Antarctic and adjacent ocean biota, but populations may have independent evolutionary lines and population dynamics.