Showing papers in "Polar Biology in 1992"
TL;DR: In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined.
Abstract: The sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2 before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean.
498 citations
TL;DR: The question of limitation of the primary production by eolian-transported trace-metals in these different sub-systems is still a matter of debate, although clear iron limitation has been evidenced for offshore waters of the Ross Sea.
Abstract: Four major functional units have been identified in the Southern Ocean and the mechanisms that control the dynamics of nutrients and phytoplankton are detailed for the different sub-systems. The very productive Coastal and Continental Shelf Zone (CCSZ, 0.9 M km 2) can experience severe macronutrient depletion paralleling intense diatom-dominated phytoplankton blooming (maximum > 8 mg Chl a m−3) at the ice edge. In the Seasonal Ice Zone (SIZ, 16 M km 2) dramatic variations in the hydrological structure occur in surface waters during the spring to summer retreat of the pack-ice, changing from a well-mixed system to a stratified one within the reaches of the ice edge. Grazing activity of euphausiids limits phytoplankton biomass to a moderate level (Chl a maximum around 4mg m−3). A shift from new production to a regenerated production regime has been demonstrated during spring, along with the key role played by protozoans in controlling high ammonium concentrations (maximum > 2 μM) in the surface layers. The well-mixed Permanently Open Ocean Zone (POOZ, 14 M km 2) is characterised by variable N/Si ratios in surface waters along a north-south transect: at the northern border of the POOZ (N/Si = 0.25) silicate concentrations as low as <10 μM could help limit the phytoplankton growth. Although favourable conditions have been demonstrated for the initiation of blooms in spring in the Antarctic Circumpolar Current, it appears that critical-depth/ mixing-depth relationships control maximum chlorophyll a concentrations < 1 μg l−1 during summer. The POOZ is usually not influenced directly by euphausiids, except for the Scotia Sea and Drake Passage where migrations of krill from the adjacent SIZ are usual. Mesoscale eddies are typical of the Polar Front Zone (FPZ, 3 M km 2): significant increases in phytoplankton biomass have been reported in this frontal area (maximum Chl a = 2 mg m−3). Food web and biogeochemical cycles in this sub-system are poorly documented. The question of limitation of the primary production by eolian-transported trace-metals in these different sub-systems is still a matter of debate, although clear iron limitation has been evidenced for offshore waters of the Ross Sea.
340 citations
TL;DR: There is a need to pay close attention to environmental data in the management of Southern Ocean resources given the complexity of relating biological changes to ecological perturbations.
Abstract: A central tenet of Antarctic ecology suggests that increases in Chinstrap Penguin (Pygoscelis antarctica) populations during the last four decades resulted from an increase in prey availability brought on by the decrease in baleen whale stocks. We question this tenet and present evidence to support the hypothesis that these increases are due to a gradual decrease in the frequency of cold years with extensive winter sea ice cover resulting from environmental warming. Supporting data were derived from one of the first, major multidisciplinary winter expedition to the Scotia and Weddell seas; recent satellite images of ocean ice cover; and the analysis of long-term surface temperature records and penguin demography. Our observations indicate there is a need to pay close attention to environmental data in the management of Southern Ocean resources given the complexity of relating biological changes to ecological perturbations.
313 citations
TL;DR: In this paper, the authors characterize the habitats and communities and suggest some standard terms for them, and also suggest routine sampling methods and reporting units for measurements of biological and chemical variables.
Abstract: Polar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables. © 1992 Springer-Verlag GmbH & Co. KG.
237 citations
TL;DR: This paper focusses on the links between growth, persistence and decay of sea ice and the structure of Antarctic marine ecosystems on different spatial and temporal scales.
Abstract: This paper focusses on the links between growth, persistence and decay of sea ice and the structure of Antarctic marine ecosystems on different spatial and temporal scales. Sea-ice growth may divide an oceanic ecosystem into two dissimilar compartments: (1) the water column, with primary production controlled by the reduction of irradiative fluxes due to the snow-laden sea-ice cover and thermo-haline convection, and (2) the pore space within the ice with incorporated organisms switching from a planktonic to a “kryohaline” mode of life. In the ice, physical boundary conditions are set by (1) the irradiance which is controlled by the optical properties of snow and ice and (2) the ambient temperature which controls salinity and brine volume. Partly due to the high levels of biomass within the sea-ice system, interaction between different groups of organisms concentrates on the planar environment predefined by the ice cover. As a resuit of regional structuring of ecosystems, four sea-ice regimes may be recognized: seasonal pack ice, coastal zone, perennial pack ice, and marginal ice zone. These regimes are interwoven through the temporal structuring of ecosystems brought about by ice-cover seasonality and ice drift. In comparison with open-water pelagic ecosystems, sea ice appears of particular importance as it partly inverts the ecosystem structure and enhances the degree of ecological variability.
189 citations
TL;DR: The data support the idea of a light-dependent DMSP biosynthesis, and demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae.
Abstract: The effect of photon fluence rate on the s-dimethylsulphoniopropionate (DMSP) content of salt-stressed eulittoral green macroalgae from different geographic regions was determined. At 55 μmol photons m−2s−1 DMSP increased continuously with increasing salinities up to 68‰ in Ulothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa and Acrosiphonia arcta from Antarctica, while the Subantarctic/cold-temperate Ulva rigida and the temperate Blidingia minima showed a large rise in intracellular DMSP concentration only under gentle hypersaline treatment (51‰). At the highest salinity tested the DMSP content of the latter species declined. In contrast, the capacity to form DMSP in the dark under hypersaline conditions was very low in all species. In addition, the DMSP content of the Antarctic species was determined after one year cultivation at 0°C under photon fluence rates of 2, 30 and 55 μmol m−2s−1. All isolates increased their DMSP concentration with increasing irradiance. In contrast to previous experiments done at 10°C, these species exhibited up to 5 fold higher DMSP values at 0°C under most photon fluence rates. The data support the idea of a light-dependent DMSP biosynthesis, and also demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae. Apparently, in these plants DMSP may function as a cryoprotectant.
125 citations
TL;DR: The ability of cyanobacterial mats from Antarctic ponds and streams to recover from desiccation is described and partial hydration during aerial exposure improved the survival of Phormidium mats, but appeared to slow the recovery of Nostoc mats on subsequent rewetting.
Abstract: The ability of cyanobacterial mats from Antarctic ponds and streams to recover from desiccation is described. Mats dominated by Nostoc dehydrated rapidly and were dry within 5 h of exposure. Nostoc mats recovered to pre-desiccation rates of photosynthesis and respiration within as little as 10 min of rewetting. Recovery of acetylene reduction activity was slower (>24 h). Phormidium dominated mats were less tolerant of desiccation, and recovery on rewetting from air-drying was not complete after 10 days. Viable diaspores were, however, found in Phormidium mats which had been exposed for 3 years. Partial hydration during aerial exposure improved the survival of Phormidium mats, but appeared to slow the recovery of Nostoc mats on subsequent rewetting.
119 citations
TL;DR: Between January and March 1989, a hydrographic survey was carried out in the southeastern Weddell Sea on transects across the continental shelf and slope off Kapp Norvegia and Halley Bay, representing oceanographic conditions during Antarctic summer.
Abstract: Between January and March 1989 during EPOS leg 3, a hydrographic survey was carried out in the southeastern Weddell Sea on transects across the continental shelf and slope off Kapp Norvegia and Halley Bay This data set represents oceanographic conditions during Antarctic summer Winter observations were obtained during the Winter Weddell Gyre Study in September and October 1989 During summer the water in the surface layer is relatively warm and of low salinity In the area of Halley Bay exceptionally warm conditions were encountered with sea surface temperatures of nearly + 1°C Over the upper continental slope a frontal zone separates Eastern Shelf Water from Antarctic Surface Water in the near surface layer and from Warm Deep Water in the deeper layers The horizontal pressure gradient associated with the front produces the high velocity core of the Antarctic Coastal Current In winter Antarctic Surface Water is replaced by colder Winter Water of higher salinity Measurements from current meters moored off Kapp Norvegia and Vestkapp are used to describe the mean features of the current field and its fluctuations At Kapp Norvegia annual mean current speeds range from 10 to 20 cm/s The geostrophic current shear indicates that the speed of the current core decreases towards Halley Bay The currents show significant seasonal variations with strong interannual differences These compare well with the variations of the wind field observed at the Georg von Neumayer Station Superimposed are higher frequency fluctuations with an energetic range between 5 and 15 days which is found in the wind measurements as well A considerable part of the current velocity variance is due to the tides The oceanographic conditions are strongly influenced by the local bottom topography A topographic rise at the shelf edge off Kapp Norvegia reduces horizontal advection and allows a patch of cold Winter Water to be preserved into the summer In contrast, a patch of Warm Deep Water was found on the shelf of Halley Bay This illustrates rather heterogeneous conditions in the near bottom layers due to differences in the exchange rate with the open ocean as well as with the near surface layers
116 citations
TL;DR: A total of 233 multibox corer samples from 36 stations along the southeastern Weddell Sea shelf and upper continental slope between Atka Bay and Gould Bay, covering a depth range from 170 to 2,037 m, provided biomass and abundance data for analysis of faunal communities.
Abstract: A total of 233 multibox corer samples from 36 stations along the southeastern Weddell Sea shelf and upper continental slope between Atka Bay (70°S) and Gould Bay (78° S), covering a depth range from 170 to 2,037 m, provided biomass and abundance data for analysis of faunal communities. Twenty-eight major taxa were distinguished. Based on these data, 3 different macrobenthos communities could be identified by means of cluster analysis. Hexactinellid sponges, polychaetes and echinoderms were most abundant. Biomass values have been found to be in the range of 94 mg up to 1.6 kg wet weight per sqm. According to TWINSPAN, the sampled stations can be divided into two groups each consisting of two major subgroups. Peracarid crustaceans, polychaetes and bivalves are commonly distributed in the area of investigation whereas others such as sponges, brachiopods, pantopods and asteroids are more confined to Kapp Norvegia and Halley Bay. Biomass values of these latter taxa off Kapp Norvegia were generally higher than in the Halley Bay area.
110 citations
TL;DR: The summer diets of four seabird species collected in sea-ice-covered waters near Svalbard are described, finding that Black Guillemots and Kittiwakes fed on fish, whereas Brünnich's Guillemot fed on the larger, and Little Auks on the smaller, Crustacea.
Abstract: We describe the summer diets of four seabird species. Kittiwake (Rissa tridactyla), Little Auk (Alle alle), Black Guillemot (Cepphus grylle) and Brunnich's Guillemot (Uria lomvia) collected in sea-ice-covered waters near Svalbard. Birds collected in an area filled with young sea-ice, within the seasonal sea-ice zone, were compared with birds collected from the perennial sea-ice zone dominated by multiyear ice. Pelagic Crustacea and fish dominated the diet of birds feeding in young ice, while sympagic Crustacea and fish were most important in the diet of birds feeding in multiyear ice. Boreogadus saida was the most important fish food item. B. Saida was present in the ice in both areas, while sympagic Crustacea were lacking in the area filled with young ice. Important food items in young ice were B. saida (Black Guillemots and Kittiwakes), Cajanus sp. (Little Auks) and Pandalus borealis (Brunnich's Guillemot). B. saida (Black Guillemots, Kittiwakes, Brunnich's Guillemots), Gammarus wilkitzkii (Brunnich's Guillemot, Black Guillemot) and Apherusa glacialis (Little Auk) were most important in multiyear ice. In general, Black Guillemots and Kittiwakes fed on fish, whereas Brunnich's Guillemots fed on the larger, and Little Auks on the smaller, Crustacea. The importance of sympagic species in the diet of seabirds is thought to be closely related to the age and history of the ice in the feeding area.
104 citations
TL;DR: Diatom abundance was dominated by the pennate diatom, usually nanoplanktonic, Fragilariopsis cylindrus (Grunow) Krieger, during all five cruises, suggesting that the ice-edge pulses of diatom assemblages in the water column largely reflected its abundance.
Abstract: Planktonic diatoms were sampled in the ice-edge zone of the Bellingshausen Sea during the early austral spring of 1990 and of the Weddell Sea during the late spring of 1983, the autumn of 1986, and the winter of 1988. The four cruises in the Antarctic marginal ice edge zones, combined with the summer cruise in Prydz Bay during a brief ice-free period (1988) provided us with opportunities for spatial and seasonal studies of diatom abundance and distribution in the water column. Cells from discrete water samples from 73 stations near the marginal ice-edge zones during all seasons were counted to gain quantitative information on the composition, abundance, and distribution of diatoms. Diatom abundance was dominated by the pennate diatom, usually nanoplanktonic, Fragilariopsis cylindrus (Grunow) Krieger, during all five cruises. The highest integrated numbers of F. cylindrus were found during the summer cruise with 7.9 × 1010 cells m−2 and the lowest numbers were found during the winter cruise with 1.1 × 108 cells m−2. The average integrated abundance of F. cylindrus from the five cruises was about 35% of the total diatom abundance. The overall spatial pattern of F. cylindrus near the marginal ice-edge zones during the five seasonal cruises were similar with the highest number of cells in open waters compared to ice-covered waters. When all 73 stations during the five cruises were included in the correlation analysis, the abundance of total diatoms was positively correlated with the abundance of F. cylindrus, suggesting that the ice-edge pulses of diatom assemblages in the water column largely reflected its abundance. Cluster analysis revealed that the stations in marginal ice-edge zones were not only separated by seasons and locations, but they also separated based on location of stations in relation to the ice edge (open water stations vs. ice-covered stations).
TL;DR: Bacterial utilization of carbon substrates and microheterotroph grazing of bacteria and uptake of DOC may form an important link to higher trophic levels during Antarctic Phaeocystis blooms.
Abstract: Changes in the concentrations of bacteria, phytoplankton, protozoa, dissolved organic carbon (DOC), particulate organic carbon (POC), particulate carbohydrate (PCHO) and particulate organic nitrogen (PON) were followed throughout the summer at an Antarctic coastal site. The colonial prymnesiophyte Phaeocystis pouchetii was the first major phytoplankton species to bloom, reaching concentrations of 6 × 107 cells · 1−1 and remained numerically dominant for most of the summer. During the P. pouchetii bloom the concentration of most other autotrophs did not increase. Microheterotroph abundance peaked during or immediately after the Phaeocystis bloom. Their peak coincided with very high concentrations of organic carbon, particularly DOC which exceeded 100 mg · 1−1, and low bacterial abundance. Maximum bacterial abundance was reached after the decline in microheterotroph numbers. Bacterial utilization of carbon substrates and microheterotroph grazing of bacteria and uptake of DOC may form an important link to higher trophic levels during Antarctic Phaeocystis blooms.
TL;DR: It is suggested that the distinct diel pattern of dive timing and depth may be related to possible predator avoidance behavior by the seals' principal prey, Antarctic Krill.
Abstract: Time-depth recorders were used to study the diving and haulout behavior of six crabeater seals in the marginal. ice edge zone of the Weddell Sea during March 1986. Haulout patterns revealed the seals' clear preference for diving during darkness and hauling out onto sea ice during daylight. Seals did not necessarily haul out every day; individual seals hauled out on 80–100% of days during the study period. Four general dive types were identified: 1) traveling dives, 2) foraging dives, 3) crepuscular foraging dives, and 4) exploratory dives. Nearly continual diving occurred for extended periods (about 16 h) nightly, with one individual diving up to 44 h without interruption. Foraging dives occurring during crepuscular periods were deeper than those made during the darkest hours. The authors suggest that the distinct diel pattern of dive timing and depth may be related to possible predator avoidance behavior by the seals' principal prey, Antarctic Krill.
TL;DR: Diatoms (in particular Nitzschia and Thalassiosira spp.) contributed by far the bulk of material in krill and oval faeces and highest concentrations were always found in the Confluence often close to the ice border.
Abstract: The abundance and depth distribution of zooplankton faeces in spring to early summer were investigated along meridional transects (47°W and 49°W) that extended from the Scotia Sea (57°S) across the Weddell-Scotia Confluence and into the Weddell Gyre (62° S). The sea ice edge retreated from 59°30′S to 61°S during the study. Faeces were sampled with nets, Niskin bottles and sediment traps and subsequently analysed by light and electron (SEM) microscopy. Krill faecal strings and oval faecal pellets of unknown origin were by far the most important zooplankton faeces and highest concentrations were always found in the Confluence often close to the ice border. Krill faeces were usually more abundant in the uppermost layer (0–50 m) where they contributed an average of 130 μg dry weight m−3. There was an exponential decrease with depth, with a minimum of 0.6 μg dry weight m−3 in the 500–1000 m stratum. Oval pellets were more evenly distributed in the upper 1000 m of the water column, with an average of 9 μg dry weight m−3, although there was a small peak (20 μg dry weight m−3) in the subsurface layer (50–150 m depth). Consecutive collections (day-night) of krill faeces using drifting sediment traps showed that only the larger strings sank from 50 to 150 m depth. Peritrophic membranes appeared to deteriorate during sinking. Diatoms (in particular Nitzschia and Thaiassiosira spp.) contributed by far the bulk of material in krill and oval faeces. In samples collected near or under the pack ice, remains of crustaceans in both krill- and oval faeces were also found.
TL;DR: Adaptation experiments showed that some ice algae are highly adaptable, while others are not able to adjust to new irradiances, and this may affect the distribution in the field.
Abstract: The ice algae of the Barents Sea were studied from 1986 to 1988. With a few exceptions, the ice algal assemblages were dominated by pennate diatoms. From March to early June there was a transition from a mixed population of both centric and pennate diatoms at the start into a well developed Nitzschia frigida assemblage. Nutrier ts in ice-covered regions were high in spring, and high N/C and protein/carbohydrate ratios indicated no nutrient deficiency in the ice algae. The N/P ratios were lower than 15, but comparable to ratios of three ice algae species grown in culture at -0.5 °C and various light conditions. The Si/N ratios were lower than corresponding ratios from the Canadian Arctic and the Antarctic. The chemical composition revealed that silicate limited growth cannot be excluded. The cells were heavily shade-adapted the entire spring season, with high Chl/C ratios (0.045–0.084), comparable to the cultures growing at low irradiances. The growth rates in the cultures peaked at 50 μmol m-2s-1 with maximum rates of 0.6–0.8 div. day-1, both for 12 and 24 h day lengths. The low growth rates for the May assemblages (max 0.20 div. day-1) indicated strong light limitation by self-shading. Adaptation experiments showed that some ice algae are highly adaptable, while others are not able to adjust to new irradiances. Their growth rates are inhibited by high irradiances and this may affect the distribution in the field.
TL;DR: High Antarctic representatives of these two species grow to a larger maximum size, attain sexual maturity later in their life cycle, and produce fewer and larger eggs in relation to both carapace length and female mass, than their Subantarctic counterparts.
Abstract: Data on reproductive biology are presented for five benthic caridean shrimps from the high Antarctic (Chorismus antarcticus, Notocrangon antarcticus, Nematocarcinus lanceopes, Lebbeus antarcticus and Eualus kinzeri). The first three species were very common on the Weddell Sea shelf and upper slope, whereas only a few individuals of the other two species were caught-but these did include some ovigerous females. Our measurements include size at first maturity, fecundity (total number and mass of eggs), individual egg mass, egg length, ovary indices, maximum size encountered and documentation of the reproductive cycle in spring and summer. Egg number generally increases with female size, and the largest species (N. lanceopes) also carries the highest number of eggs. The eggs of all high Antarctic species are large, the extreme being L. antarcticus with an egg length of up to 3.3 mm. For C. antarcticus and N. antarcticus, which have wide geographic distributions, a comparison is made with older published and unpublished data from the Subantarctic (South Georgia). High Antarctic representatives of these two species grow to a larger maximum size, attain sexual maturity later in their life cycle, and produce fewer and larger eggs in relation to both carapace length and female mass, than their Subantarctic counterparts.
TL;DR: Free-floating sediment traps used on a transect from Scotia Sea to Weddell Sea collected larger, more degraded, krill faecal strings in the deeper traps than in the 50 or 75 m traps, with relatively high settling velocities.
Abstract: Free-floating sediment traps used on a transect from Scotia Sea to Weddell Sea collected larger, more degraded, krill faecal strings in the deeper (150 m) than in the 50 or 75 m traps. The smallest faecal strings were only present in the shallower traps. Sinking velocity of smaller faecal strings was - as expected - much lower than for larger ones, with a total range of 50 to 800m-day−1 for faecal string volumes of 0.007 to 0.53 mm3. Krill feeding largely on diatoms produced faeces with higher settling velocity than those feeding on non-diatom phytoplankton. Smaller krill faecal strings do not leave the upper mixed layer. Potential settling velocities as measured in settling tubes (without turbulence), may in this respect be misleading. Small oval faecal pellets of unknown origin showed relatively high settling velocities (80 to 250 m day1 for 0.002 to 0.013 mm3) due to higher compaction and lower form resistance to sinking.
TL;DR: The results show that not all marine invertebrates living in cold water environments produce large eggs, provide postspawning parental care or lack planktonic larvae (Thorson’s rule), nor that brooding behaviour is always associated with small adult size.
Abstract: The reproductive modes of 66 molluscan species from the Weddell Sea, Antarctica were investigated either by rearing of specimens in aquaria (“Neomenio-morpha” [Solenogastres], Polyplacophora and Gastropoda) or by studies of the larval shell (Bivalvia). The results show that not all marine invertebrates living in cold water environments produce large eggs, provide postspawning parental care or lack planktonic larvae (Thorson’s rule), nor that brooding behaviour is always associated with small adult size. Several lecithotrophic (Solenogastres, Polyplacophora) and meroplanktonic, planktotrophic larvae (Gastropoda) were observed in aquaria. Investigations of the larval shell morphology indicate a planktotrophic or lecithotrophic larval stage in 27 Bivalvia species. With exception of two species of meroplanktonic gastropod larvae no developmental stages of benthic molluscs were ever found in plankton hauls in the Weddell Sea. This indicates that most larvae may live demersally. Brooding occurred in 1 Monoplacophora and 17 Bivalvia species. Intracapsular metamorphosis with very long embryonic development was observed in 15 Gastropoda species.
TL;DR: The highest rate of decrease observed on the Crozet Archipelago and the fact that the population is still decreasing may be explained by additional factors, in particular by killer whale predation.
Abstract: The elephant seal populations breeding on the Crozet and Kerguelen Archipelago were surveyed during the eighties. Elephant seals were observed moving between Kerguelen, Amsterdam, Heard Islands and Vestfold Hills and between Crozet and Prince-Edward Archipelagos. No exchanges were observed between Crozet and Kerguelen Archipelagos suggesting that the two populations are more isolated than previously stated. On the Crozet Archipelago, since 1966, the Possession Island population showed at 70% reduction in numbers of cows ashore and the population is still decreasing. On Kerguelen Island there has been a decline of 44% from 1956 to 1989 but the population appears to have stabilized since 1984. It is suggested that elephant seal populations in the Southern Indian Ocean may have been affected by a change at the trophic level over the last four decades. But the highest rate of decrease observed on the Crozet Archipelago and the fact that the population is still decreasing may be explained by additional factors, in particular by killer whale predation.
TL;DR: Investigation of within-AFC patterns indicates that the continent is a highly homogeneous area, establishing closer relationships with the Scotia Arc and to a lesser extent with the Magellan region, which may lead to a common Gondwanian origin for Antarctic and circumantarctic sponge faunas, followed by differentiation due to Gondwana fragmentation.
Abstract: The biogeography of Antarctic demosponges has been studied by dividing Antarctic and circumantarctic areas into geographic entities, and then assigning to these entities all recorded species according to literature reports. Correspondence analysis ordination based on the presence or absence of species shows the existence of a distinct Antarctic Faunistic Complex (AFC), including continental Antarctica, most of the Antarctic and circumantarctic islands and the Magellan area. Such a result has enabled us to drawup a checklist of 352 Antarctic demosponge species. Investigation of within-AFC patterns indicates that the continent is a highly homogeneous area, establishing closer relationships with the Scotia Arc and to a lesser extent with the Magellan region. The AFC has low specific affinities with the other circumantarctic regions (South Africa, temperate Australia and New Zealand), whereas at the generic level relationships appear more pronounced. This biogeographic pattern may lead us to suppose a common Gondwanian origin for Antarctic and circumantarctic sponge faunas, followed by differentiation due to Gondwana fragmentation. Antarctica moved towards polar latitudes and became progressively isolated, only maintaining active interchanges with South America. Climatic changes possibly induced intense processes of speciation in the Antarctic demosponge fauna, thus contributing to its differentiation.
TL;DR: The quantitative importance of the nanophytoplankton groups reported here underlines the diversity of the plankton in the Southern Ocean’s marginal ice zone system which may have implications for food chain dynamics.
Abstract: During a cruise in the Weddell-Scotia Confluence area (EPOS Leg 2 : November–January 1988/1989) nanophytoplankton composition was determined by employing taxon-specific pigment measurements with HPLC. The biomass of the most important components was estimated by using specific pigment ratios measured in cultures of two cryptomonads and a prasinophyte. Highest cryptophyte biomass was found along the retreating ice-edge; the contribution of cryptophytes to total phytoplankton crop increased with time, reaching monospecific bloom conditions at the end of the cruise. Chlorophyll b-containing organisms and Prymnesiophyceae were present everywhere and dominated in the ice-covered part of the survey area. Cryptophyte-specific pigment measurements were in reasonable agreement with cryptophyte cell numbers. Prasinophyte cell counts, however, did not match with measured chlorophyll b concentrations. The quantitative importance of the nanophytoplankton groups reported here underlines the diversity of the plankton in the Southern Ocean’s marginal ice zone system which may have implications for food chain dynamics.
TL;DR: The enhanced phytoplankton biomass in theWeddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.
Abstract: Phytoplankton biomass and distribution of major phytoplankton groups were investigated in relation to sea ice conditions, hydrography and nutrients along three north-south transects in the north western Weddell Sea in early spring 1988 during the EPOS Study (European Polarstern Study), Leg 1. Three different zones along the transects could be distinguished: 1) the Open Water Zone (OWZ) from 58° to 60°S with high chlorophyll a concentrations up to 3.5 μg 1−1; 2) the Marginal Ice Zone (MIZ) from 60° to about 62.5° with chlorophyll a concentrations between 0.1 and 0.3 μg 1−1, and 3) the closed pack-ice zone (CPI) from 62.5° to 63.2°S with chlorophyll a concentrations below 0.1 μg 1−1. Nutrient concentrations increased towards the south showing winter values under the closed pack-ice. Centric diatoms such as Thalassiosira gravida and Chaetoceros neglectum forming large colonies dominated the phytoplankton assemblage in terms of biomass in open water together with large, long chain forming, pennate diatoms, whereas small pennate diatoms such as Nitzschia spp., and nanoflagellates prevailed in ice covered areas. Fairly low concentrations of phytoplankton cells were encountered at the southernmost stations and many empty diatom frustules were found in the samples. The enhanced phytoplankton biomass in the Weddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.
TL;DR: It is concluded that, in this area, summer water flow in conjunction with microtopography has the greatest influence in determining where mosses, cyanobacteria and algae grow.
Abstract: Bryophyte flushes in the vicinity of Canada Glacier in S.S.S.I. No. 12, Taylor Valley, Southern Victoria Land, were investigated in order to describe the vegetation present and to investigate factors affecting vegetation distribution. Biomass values from 950 to 1,250 g m−2 (dry weight) and vegetated areas up to 14,450 m2 indicate this is a significant area of bryophyte growth in Southern Victoria Land. The pattern of plant species in relation to water flow was investigated through detailed mapping. This is the first confirmed identification of Bryum argenteum, and Pottia heimii, and the first report of Bryum pseudotriquetrum from this area. Tissue nitrogen values for plants at this site are lower than other reported data, but it seems unlikely this would be a limiting factor for growth. It is concluded that, in this area, summer water flow in conjunction with microtopography has the greatest influence in determining where mosses, cyanobacteria and algae grow.
TL;DR: During the third leg of the “European Polarstern Study” (EPOS leg 3) in the austral summer season 1989, benthic macrofaunal communities were sampled from the Elephant Island area and from Kapp Norvegia to Halley Bay using a commercial bottom trawl and an Agassiz trawl.
Abstract: During the third leg of the “European Polarstern Study” (EPOS leg 3) in the austral summer season 1989, benthic macrofaunal communities were sampled from the Elephant Island area (61° southern latitude) and from Kapp Norvegia (71° southern latitude) to Halley Bay (75°30′ southern latitude) using a commercial bottom trawl and an Agassiz trawl. Thirty-six trawl samples from a depth range of about 200–2,000 m were considered, with most of the samples being from the shelf and upper slope. Multivariate analysis techniques (clustering and TWIN-SPAN) discriminated between an eastern and a southern community in which parallel subgroups can be distinguished at increasing distance from the ice shelf.
TL;DR: Predicted aerobic dive limits suggested that during long dives, blue-eyed shags were probably sustained by anaerobic metabolism, and predicted capture rates for the commonest recorded prey (small fish) differ markedly between the two diving strategies.
Abstract: This paper describes a concurrent investigation of individual variation in diet, diving patterns and performance of blue-eyed shags Phalacrocorax atriceps breeding at South Georgia. Within one day individual shags exhibited one of three foraging strategies: short diving (4 birds, all dives 120 s) and mixed diving (15 birds, predominantly long but with a few short dives). The mean number of dives per day was significantly higher in shags that only made short dives (mean=172.0, SE=43.2) than birds with a mixed diving strategy (mean=40.5, SE=4.7) and birds that made only long dives (mean=30.8, SE=1.8). Diet was assessed using hard remains recovered from pellets regurgitated by the shags. Small nototheniid fish (c. 10 kJ per item) were by far the commonest prey but most pellets contained additional items. The frequency of pellets with additional items of higher energy value than nototheniid fish (10.c. 900 kJ per item), lower energy value (>1–10 kJ per item) and both higher and lower energy items was strikingly similar to the frequency of shags making long, short and both long and short dives respectively. Predicted aerobic dive limits suggested that during long dives, blue-eyed shags were probably sustained by anaerobic metabolism. Models of prey capture rates demonstrated that for both long and short diving, many items must be caught per dive when birds are feeding on prey at the lower end of the energy range. Predicted capture rates for the commonest recorded prey (small fish) differ markedly between the two diving strategies.
TL;DR: The results clearly indicated that a large majority of the bacteria isolated from seawater must be considered psychrotrophic but that truly psychrophilic strains occurred in melted ice and brine samples.
Abstract: In the eastern Weddell Sea on several transects from ice-covered, through ice melt, to open-ocean stations, total and heterotrophic bacteria were estimated to document an enhanced bacteriological biomass expected near the ice edge. The highest numbers of bacteria were found in melted ice cores, with 4.2·103 CFU ml-1 and 1.1·107 Cells ml-1 Although brine from pore water samples average more than one order of magnitude less cells per ml, the highest bacterial production, 2.2·107 cells 1-1 day-1, was recorded in brine samples. All quantitatively studied bacterial parameters were lower under the ice than in the ice samples but there were no clear vertical gradients in the water column. In the studied spring situation, sea ice occurrence seems to play only a minor role in the general distribution of the seawater bacterioplankton. The bacterial community structure was investigated by carrying out 29 morphological and biochemical tests on 118 isolated strains. The bacterial communities inhabiting Antarctic pack ice differ from those found in underlying seawater. Although non fermentative Gram-negative rods were always dominant in seawater, Vibrio sp. represented more than 25% of the strains isolated from some ice samples. The results clearly indicated that a large majority of the bacteria isolated from seawater must be considered psychrotrophic but that truly psychrophilic strains occurred in melted ice and brine samples.
TL;DR: Multivariate analysis discriminates between three communities which are correlated with depth and sediment characteristics: the near shelf-ice, the slope and the deep-sea communities.
Abstract: Meiofauna communities from 10 stations along a depth transect from approximately 500 to 2,000 m off the Halley Bay Station (Weddell Sea) are investigated. Representatives of about 30 smallsized taxa of higher category are found, most of them belonging to the meiofauna. Loricifera are recorded for the first time for the Southern Ocean. At one of the stations a maximum of 22 taxa occur, the mean number of taxa ranges from 7 to 16. Nematoda, Harpacticoida, Ostracoda, Polychaeta and Bivalvia are present at all sampling sites. Nematodes are always dominant representing more than 90% of the individuals per sample, followed by harpacticoids (3%) and kinorhynchs (1.2%). Important fractions of the meiofauna (an average of more than 50%) occur in strata below the top 0–1 cm layer. Maximal density is 3,800 individuals (10 cm−2), the mean abundance per station ranges from 790 to 3,720 individuals (10 cm−2) and the overall mean is 1,700 individuals (10 cm−2). Multivariate analysis (TWINSPAN, Cluster analysis, DCA) discriminates between three communities which are correlated with depth and sediment characteristics: the near shelf-ice, the slope and the deep-sea communities.
TL;DR: Krill was the only species with increasing abundance in the sub-ice area and a dominance in biomass of more than 91% demonstrated its unique importance for theSub-ice habitat.
Abstract: The present paper describes the composition, abundance, biomass and diversity of the meso- and macrozooplankton in the epipelagic zone of the open water and under the ice of the northern Weddell Sea. Samples were collected in October/November 1988 with a multiple RMT1+8 net during the European Polarstern Study (EPOS). Multivariate analysis resulted in two distinct site clusters, a northern one mainly located in the open water/marginal ice zone and a southern one extending from the marginal ice zone into the Consolidated pack-ice. Clusters were, however, faunistically coherent with a high degree in positive covariation of species. There was no basis for the separation into communities, but differences occurred on the population level in numerical abundances, biomass (wet weight) and in a shift in species dominance. Different ice zones and vertical layers were tested among each other with regard to their relative species abundance. Significant differences were found between the upper 60 m layer of the open sea, the upper 60 m layer of the closed pack-ice and the so called transitional zone. Species richness and diversity was lowest directly under the closed pack-ice. Abundance and biomass was highest in the surface layer of the open water, while both variables decreased dramatically under the ice. Copepods dominated numerically in open water, while salps dominated in biomass. Euphausia superba and Thysanoessa macrura were the dominant species in the upper water column of the closed pack-ice zone. Krill was the only species with increasing abundance in the sub-ice area and a dominance in biomass of more than 91% demonstrated its unique importance for the sub-ice habitat.
TL;DR: The results show that both species of diatom can survive in ice without forming resting spores and even grow at extremely low temperatures.
Abstract: The diatoms Nitzschia frigida and Thalassiosira antarctica grow exponentially even at temperatures between-4 and -6°C and a salinity between 73‰ and 100‰ Under these conditions the light saturation of growth is reached in continuous light at a scalar quantum irradiance of between 7 μmol·m−2·s−1 and 10 μmol · m−2 · s−1. The increase in salinity retards growth more than a decrease in temperature. For N. frigida the limit of growth is at -8°C (S = 145%.). At increasing quantum irradiance, the chlorophyll content per unit cell volume decreases, whereas there is a significant increase in the carbon content of the exponentially growing cells. In addition, there is hardly any change in the protein content. The results show that both species of diatom can survive in ice without forming resting spores and even grow at extremely low temperatures.
TL;DR: It is suggested that temperature, moisture, moisture (and the frequency and amplitude of fluctuations in these), pH, and biogeographical factors may be significant influences on the distribution and abundance of testate rhizopod species in continental Antarctica.
Abstract: New records are presented of the occurrence of seven testate rhizopod species in terrestrial habitats in Dronning Maud Land and the Ross Dependency regions of Antarctica: Arcella arenaria, Centropyxis aerophila, Corythion dubium, Difflugia lucida, Diplochlamys timida, Heleopera petricola, Trigonopyxis arcula. All materials examined showed very low species-richness and very low populations (except Arcella arenaria in Bryum moss in Southern Victoria Land) compared with records from other parts of the world. Pooling present results with previous records gives a species list to date of 26 for continental Antarctica. These data are interpreted in light of knowledge of species records from peri-Antarctic islands, Arctic and Alpine regions. It is suggested that temperature, moisture (and the frequency and amplitude of fluctuations in these), pH, and biogeographical factors may be significant influences on the distribution and abundance of testate rhizopod species in continental Antarctica.