Summer diet of Weddell Seals (Leptonychotes weddelli) in the eastern and southern Weddell Sea,Antarctica

Summary Stomach and intestine samples from 21 adult Weddell seals were used to study the diet of these seals from the eastern and southern Weddell Sea coast from January to February 1983 and 1985. Fish occurred in all seals, squid in five, octopods in three and Euphausia crystallorophias in one seal. Pleuragramma antarcticum was the predominant fish in the diet, constituting 61.1% of otoliths in 1983 samples and 93.8% in 1985. Aethotaxis mitopteryx, Dissostichus mawsoni, unidentified Trematomus spp. and channichthyids were also recorded. Size and wet weight of P. antarcticum were calculated from uneroded otoliths, found in 6 seal stomachs with liquid food pulp, collected during early morning hours in 1985. Size distribution of P. antarcticum from individual seals was reasonably constant, ranging between 5.0 and 22.0 cm SL; adult fish from about 14.0 to 19.0 cm SL predominated. P. antarcticum in seals from the southern area had a larger median size (16.5 cm SL), than those from further east (15.5 cm SL). Calculated wet weights of all P. antarcticum from individual seal stomachs ranged between 4.7 and 16.9 kg the mean was 12.8 kg. Comparisons with net-hauls from the southern Gould Bay suggest that Weddell seals feed mainly in deeper water layers (>400 m) where adult P. antarcticum occur at higher densities.     

Vertical distribution and abundance of juvenile chaetognaths in the Weddell Sea (Antarctica)

The composition, abundance and vertical distribution of chaetognaths were analysed along a transect in the Weddell Sea during late spring. Three species were identified: Eukrohnia hamata (90.8%), Sagitta marri (6.4%) and S. gazellae (2.8%). Only juvenile stages were collected in the samples, a result related both to the type of sampling gear employed (mesh size: 100 μm) and the species' life-cycles. The vertical distributions showed that the juvenile stages of these species tended to aggregate at considerable depth (1000–500 m). It is postulated that this pattern may be related to the life-cycles of these species in association with seasonal Antarctic conditions, similar to the pattern postulated for krill and other polar crustaceans. Accepted: 10 July 2000     

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     

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.     

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.     

A new species of Hormathia (Actiniaria, Hormathiidae) from the eastern Weddell Sea, Antarctica

A new species of sea anemone in the genus Hormathia, is described and illustrated based on forty-two specimens collected during the Polarstern cruises ANT XV/3 and ANT XVII/3 in the Weddell Sea. The main features of the new taxon are the crown of flattened and hooked tubercles at the distal end of the scapus, the regular arrangement of pointed tubercles along the column and the cnidom. The new species shares the pointed tubercles, at least in the upper part of the scapus, with two other species of Hormathia in the southern hemisphere: Hormathia spinosa Hertwig 1882 and H. pectinata Hertwig 1882 Received in revised form: 27 December 2000 Electronic Publication     

Copepods in summer platelet ice in the eastern Weddell Sea,Antarctica

Copepods in platelet-ice layers underlying fast ice and in the water column below were studied at Drescher Inlet, eastern Weddell Sea in February 1998. Three copepod species were found: Drescheriella glacialis and Paralabidocera antarctica occurred in platelet-ice layers, while Stephos longipes was only present in the water column. The distribution of all species varied considerably between station and depth. D. glacialis dominated the platelet-ice community and occurred at all five platelet-ice sampling sites, except one, with numbers of up to 26 ind. l^–1. In contrast, P. antarctica was only found in low numbers (up to 2 ind. l^–1) at one site. The total copepod abundance in the platelet ice was not associated with algal biomass, although it was strongly correlated with high ammonium concentrations (up to 9 M) in the interstitial water between the platelets. This is the first indirect evidence to support the hypothesis that zooplankton excretion can partly account for the high ammonium values often found in platelet-ice layers.     

The post-moult diet of Emperor Penguins (Aptenodytes forsteri) in the eastern Weddell Sea,Antarctica

The diet of emperor penguins Aptenodytes forsteri was studied during late austral summer at Drescher Inlet, eastern Weddell Sea, Antarctica. Antarctic krill Euphausia superba was a major component of the food, accounting for 75% of all prey items. Emperor penguins appear to feed on krill during shallow dives under the fast sea ice. Fish, mainly nototheniids, accounted for less than 20% by number of all prey. An evaluation of the main prey types in terms of mass indicated, however, that fish represented up to 75% approximately of prey mass. Feeding experiments were performed on captive penguins and showed that squid beaks can accumulate for up to 3 weeks within the stomach without any clear signs of erosion. The lack of cephalopod soft parts in the samples makes it likely that all squid beaks were derived from animals captured some time previously. Squid seems to be a very minor dietary component of emperor penguins at the Drescher Inlet.     

Sipuncula of the southeastern Weddell Sea (Antarctica)

Sipunculans collected during the EPOS (European Polarstern Study) leg 3 cruise (13.1.89–10.3.89) to the Weddell Sea shelf area from depths ranging from 186 to 2037 m are recorded. Seven species in three genera are recognized; Nephasoma capilleforme and Phascolion convestitum have not been recorded hitherto in Antarctica. Significant morphological characters as shown by light (LM) and electron (SEM) photographs are described and illustrated. Antarctic distribution maps of the species collected and a checklist of the sipunculan species south of the Antarctic Convergence with depths and bibliographic references are included.     

Peltidiidae (Copepoda, Harpacticoida) from the Weddell Sea (Antarctica)

Alteutha polarsternae sp.n. is described and Eupelte villosa (Brady, 1910) is redescribed in detail. The distribution of both these species in the Weddell Sea is recorded.     

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.     

Vertical distribution and abundance of mesoplanktonic medusae and siphonophores from the Weddell Sea,Antarctica

The composition, abundance and vertical distribution of mesoplanktonic cnidarians collected along a transect across the Weddell Sea have been analysed. The transect was characterized by a thermocline, approximately between 200 and 100 m, which deepened significantly towards the shelf edges. In total, 10 species of medusae and 18 species of siphonophores were identified. The most abundant medusae were Pantachogon scotti (up to 11,671 specimens/1,000 m³) and Arctapodema ampla (up to 960 specimens/1000 m³). The most abundant siphonophores were Muggiaea bargmannae (up to 1,172 nectophores/1,000 m³) and Dimophyes arctica (up to 230 nectophores/1,000 m³). Five assemblages of planktonic cnidarians were distinguished: (a) epipelagic species located in and above the thermocline; (b) epi- and upper mesopelagic species located in, above and just below the thermocline; (c) epi- and mesopelagic species located in and below the thermocline; (d) mesopelagic species; (e) lower mesopelagic species. Differences in the depth distribution of the various species gave rise to a clear partitioning of the mesoplanktonic cnidarian population throughout the water column. This vertical partitioning was related to the existence of a thermocline, the structure of the water column and the vertical distribution of prey.     

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.     

Stomach contents of the Antarctic Silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica)

Summary The stomach contents of 142 Pleuragramma antarcticum from the southernmost part of the Weddell Sea (Gould Bay: 77°19S) and from the eastern coast (72°–74°S) were analyzed. The fish were collected in February 1983 and stored frozen. Size range of the investigated specimens was from 6.4 cm SL (7.3 cm TL) to 21.9 cm SL (24.1 cm TL). The fish were caught by bottom trawl (Gould Bay) and Agassiz Trawl and pelagic RMT-m net in the upper 300 m layer at the eastern coast, respectively. Thirty-six stomachs were empty or contained sand only. The most important prey in terms of biomass were euphausiids, which occurred in 49 stomachs at a mean number of 2. Their dry weight was estimated to be 15–50 times that of the next important food items, which were copepods, gastropods and gammarids. Krill (Euphausia superba) constituted up to 14% of the euphausiids in the diet of fish caught in the eastern Weddell Sea. The rest was usually made up by Euphausia crystallorophias. This species was taken with preference even when the abundance of E. superba in accompanying plankton catches was 16 times higher. In the Gould Bay, gastropods were frequently eaten despite high numbers of copepods in the plankton, whereas in the eastern Weddell Sea, copepods were abundant both in plankton and in the stomach content. The almost complete absence of the early stages of fish in the diet of Pleuragramma antarcticum in the southern and eastern Weddell Sea is due to a pronounced vertical segregation of fish of different sizes. This distribution pattern is thought to be an adaptive mechanism to avoid intraspecific predation, as 90% of the ichthyoplankton in that area is Pleuragramma antarcticum.     

Nanoplanktonic coccolithophorids (Prymnesiophyceae, Haptophyceae) from the Weddell Sea, Antarctica

The examination of whole mounts prepared for transmission electron microscopy has resulted in the finding of thirteen taxa of nanoplanktonic coccolithophorids from the Weddell Sea, Antarctica. The material was collected as part of the AMERIEZ programme, March 1986. Cold-water adapted nanoplanktonic coccolithophorids have previously been shown to constitute a recurrent plankton element at subarctic and arctic localities. Three of the Weddell Sea species, Wigwamma annulifera, W. arctica , and Papposphaera sagittifera , are conspecific with northern hemisphere material, while two species, Calciarcus alaskensis and Turrisphaera arctica , are possibly identical with previously described arctidsubarctic material. Six taxa new to science have been described from the Weddell Sea, Wigwamma antarctica, W. triradiata, Trigonaspis melvillea, Pappomonas weddellensis, Papposphaera obpyramidalis , and P. simplicissima . The cooccurrence of identical forms at the two poles, and the fact that the species described are allocated to "arctic" genera, indicate a geologically relatively recent exchange of biological material between the poles.     

Distribution and abundance of the planktic foraminifer Neogloboquadrina pachyderma in sea ice of the Weddell Sea (Antarctica)

Summary Sea ice cores were obtained from eleven fast ice stations and one floe in the Weddell Sea, Antarctica in January–February 1985. All cores from the north eastern part of the Weddell Sea contained numerous living and dead planktic foraminifers of the species Neogloboquadrina pachyderma (Ehrenberg), while cores drilled in southern parts were barren of foraminifers with one exception. Foraminiferal abundances were variable, with numbers up to 320 individuals per liter melted sea ice. Distribution of foraminifers appears to be patchy, parallel cores taken less than 30 cm apart contained numbers which varied considerably. On the other hand, three cores taken on a transect each more than 3 km apart showed striking similarities. In general, small dead tests were found in the upper parts of the sea ice cores while large living individuals mainly occurred in lower sections. Abundant diatoms probably serve as a food source for the foraminifers. Correlation of foraminiferal abundance with salinity, chlorophyll and nutrient profiles are inconsistent. The possible mechanism of incorporation of N. pachyderma into the ice is discussed.     

The genus Sterechinm (Echinodermata: Echinoidea) on the Weddell Sea shelf and slope (Antarctica): distribution,abundance and biomass

Summary Two species of the echinoid genus Sterechinus were documented from 92 trawl stations and 55 photographic stations in the eastern and southern Weddell Sea between 100 and 1200 m water depth. We found two species occuring along the whole shelf and slope, S. neumayeri being more abundant above 450 m water depth and S. antarcticus dominating the deeper regions. The size-frequency distributions of both species indicate differences in growth, mortality and longevity. First estimates of abundance and biomass of S. neumayeri and S. antarcticus are 0.085 ind/m² & 0.005 gAFDW/m² and 0.022 ind/m² & 0.005 gAFDW/m², respectively.AWI Publication No. 392     

High sympagic metazoan abundance in platelet layers at Drescher Inlet, Weddell Sea, Antarctica

The metazoan fauna of platelet layers was investigated at Drescher Inlet, Weddell Sea, Antarctica in the late summer of 1995. Twenty-eight species were found, many of them new to science. The most abundant subclass was the Copepoda, of which almost 90% of the individuals belong to only three species: Drescheriella glacialis, Stephos longipes and Paralabidocera antarctica. Among copepods, Harpacticoida was the largest group, represented by 16 species. Total abundance varied between 40 and 120 individuals l⁻¹. Abundances and population structure were comparable to other especially porous sea-ice habitats. Results indicate competitive exclusion among the three dominant species. The finding of a profuse meiofauna in platelet layers may explain enigmatic concentrations of ammonium and phosphate commonly detected there. Accepted: 5 February 1999