Meso- and macrozooplankton communities in the Weddell Sea,Antarctica

Summary The present paper describes composition and abundance of meso- and macrozooplankton in the epipelagic zone of the Weddell Sea and gives a systematic review of encountered species regarding results of earlier expeditions. Material was sampled from 6 February to 10 March 1983 from RV Polarstern with a RMT 1+8 m (320 and 4500 m mesh size). In agreement with topography and water mass distribution three distinct communities were defined, clearly separated by cluster analysis: The Southern Shelf Community has lowest abundances (approx. 9000 ind./1000 m³). Euphausia crystallorophias and Metridia gerlachei are predominating. Compared with the low overall abundance the number of regularly occurring species is high (55) due to many neritic forms. Herbivores and omnivores are dominating (58% and 35%). The North-eastern Shelf Community has highest abundances (about 31 000 ind./1000 m³). It is predominated by copepodites I–III of Calanus propinquus and Calanoides acutus (61%). The faunal composition is characterized by both oceanic and neritic species (64). Fine-filter feeders are prevailing (65%). The Oceanic Community has a mean abundance of approximately 23 000 ind./1000 m³, consisting of 61 species. Dominances are not as pronounced as in the shelf communities. Apart from abundant species like Calanus propinquus, Calanoides acutus, Metridia gerlachei, Oithona spp. and Oncaea spp. many typical inhabitants of the Eastwind Drift are encountered. All feeding types have about the same importance in the Oceanic Community.     

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.     

Quantitative investigations on macrobenthos communities of the southeastern Weddell Sea shelf based on multibox corer samples

Summary 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.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Quantitative distribution of the shelf and slope molluscan fauna (gastropoda,bivalvia) of the Eastern Weddell Sea (Antarctica)

Summary A comparative analysis of the relatively rich shelled gastropod and bivalve fauna of two transects from 200 to 2,000 m in the eastern Weddell Sea was done by trawls and multibox corer. Related to the unusual shelf topography, a characteristic pattern of abundance and species richness with depth and location is evidenced. Highest values of species richness are observed near the ice-shelf edge and from the rise of the shelf to some 800 m on the slope, and lowest values between 300 and 600 m on the inner slope. This anomalous pattern, not followed by the biomass, is interpreted as a consequence of both historical factors (problems of colonization of the shelf) and present food supply. Most of the species are eurybathic and eurytopic. Generally speaking, assemblages are patchy but tend to be arranged by depth zones.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

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     

Late winter microbial communities in the western Weddell Sea (Antarctica)

Microbial communities in the water column and sea ice were studied during the EPOS-cruise on R/V Polarstern in the western Weddell Sea in late winter (October–November 1988). Samples were taken from four transects from heavy pack-ice to open water. The results indicated the important role of protozoans especially in the ice-edge area. Heterotrophic nanofiagellates, dinoflagellates, ciliates and sarcodines showed significant positive correlations with chlorophyll a. Autotrophic picoplankton and autotrophic flagellates, which were probably motile zooids of Phaeocystis pouchetii (up to 3×10⁶ cells 1^–1), were most abundant in the areas of low or medium chlorophyll a concentration. Sea ice contained high numbers of heterotrophic organisms, and the distribution of the different groups showed distinct vertical zonation. At two sites, the microbial assembly beneath the ice was clearly influenced by communities from the melting ice.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

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.     

东海大陆架鱼类群落的空间结构

根据1997～2000年东海大陆架水深30～200米海域4个航次的底拖网调查资料,运用多元分析(聚类分析和非度量多维标度(NMDS))、SIMPER以及BIO-ENV方法分析了东海鱼类群落的空间格局以及与非生物环境因子之间的关系。结果表明,东海大陆架海域鱼类群落在空间上可分为3个群落类型,分别为东海近海群落、东海大陆架外缘群落以及这两个群落之间的东海大陆架混合群落。东海大陆架鱼类群落的种类组成沿着水深梯度的变化明显,每种鱼类均有一定的水深范围。不同的流系具有不同的温盐特征,影响了鱼类的分布及其洄游,从而控制了不同鱼类群落类型的种类组成。东海大陆架鱼类群落类型中,大陆架外缘群落类型各调查季节在空间分布和种类组成上相对稳定,而东海近海群落类型和东海大陆架混合群落类型在夏季融合在一起,其它季节保持各自的空间结构。同时东海陆架区只在一种群落类型中出现的鱼类相对较少,多数鱼类同时出现在两个群落类型中或3个群落类型中,但是它们相对较集中的区域明显不同,在不同群落类型中的生物量和出现频率有很大的差异,这些鱼类在其不同的生长发育阶段由于对海洋环境的不同需求,它们根据繁殖或摄食需求而在东海陆架区范围内洄游以寻找最适的海洋环境,因此对3个群落类型定义是相对的,很难严格确定一个永久的鱼类群落地理区域,以形成相互隔离的鱼类群落,而且鱼类群落之间的边界随着季节不同发生变化。     

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.     

Meiofauna response to iceberg disturbance on the Antarctic continental shelf at Kapp Norvegia (Weddell Sea)

The impact of iceberg scouring on meiofauna communities, especially nematodes, was studied on the Kapp Norvegia shelf in the Weddell Sea, Antarctica. Three stations with different stages of recolonisation following scour were selected on the basis of seafloor video images, sediment characteristics and faunal occurrences. These stations comprised a fresh scour, an older scour, and an undisturbed control site where a sponge spicule mat covered the sediment with dense epifauna. Meiofaunal abundance and taxonomic diversity of meiofauna groups were significantly reduced in the fresh scour. The highest abundance and diversity were found in the older scour as compared with the undisturbed site. The abundance and diversity of nematodes also decreased due to scouring. The abundance in the older scour recovered to the level of the undisturbed site whereas the diversity remained low. Scouring also changed the nematode community structure, with the suborders Desmoscolecina and Leptolaimina as the most sensitive groups. In addition, scouring resulted in the decrease of selective deposit feeders and the Maturity Index. The low diversity and the change in nematode generic composition in the older scour compared with the undisturbed site, despite the complete recovery in terms of abundance, suggest that the deep continental shelf nematode community in this area is sensitive to iceberg disturbance.     

A new bryozoan genus from the Weddell Sea,Antarctica

Summary Brettiopsis gen.nov. is erected within the family Scrupariidae. Its affinities with the genera Brettia, Leiosalpinx, Brettiella, Bugulella and Scruparia are briefly discussed. Its type species, Brettia triplex Hastings, is redescribed on the basis of new material collected in the southern part of the Weddell Sea by the RV Polarsirkel. Bivalved brood chambers, previously unknown in this species, are described and illustrated.     

Species diversity and distribution within the deep-sea nematode genus Acantholaimus on the continental shelf and slope in Antarctica

Species diversity and distribution—in relation with biogeography, bathymetry and environmental characteristics—within the genus Acantholaimus were investigated on the shelf and slope (182–2,009 m) in the Weddell Sea (Kapp Norvegia and Vestkapp) and near the Antarctic Peninsula (Drake Passage and Bransfield Strait). The occurrence of the otherwise typical deep-sea genus Acantholaimus in high densities and diversity on the continental shelf is a unique feature of the Southern Ocean. Fifty-five Acantholaimus species (morpho-types) were distinguished in our study area, of which 39 were found on the shelf. The Acantholaimus communities were characterised by a high number of congeneric species and the presence of many rare species, similar to typical deep-sea communities. Fourteen species had a distribution extending from the shelf to the lower slope. High local and regional diversity was obvious and a considerable level of endemism was suggested. A negative impact of chlorophyll a concentrations, reflecting the availability of phytoplankton, was found on the Acantholaimus densities and species diversity.     

Depth-related changes to density,diversity and structure of benthic megafaunal assemblages in the Fimbul ice shelf region,Weddell Sea,Antarctica

The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha⁻¹ at 245 m to 8,895 ha⁻¹ at 510 m. While diversity was variable, with H′ ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages; a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas) but diversity was highest in intermediate areas (H′ = 2.35).     

The Antarctic coastal current in the southeastern Weddell Sea

Summary 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.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Seasonal variation in the distribution and abundance of Oithona and Oncaea species (Copepoda,Crustacea) in the southeastern Weddell Sea,Antarctica

The coupling between the seasonal distribution of dominant Oithonidae and Oncaeidae and the prevailing environmental conditions in the eastern Weddell Sea was investigated. In samples from February, a community on the shelf and in the oceanic surface layer, consisting mainly of Oithona similis and Oncaea curvata and juveniles of both genera, could be differentiated from a community found in deeper oceanic waters, consisting of Oithona frigida, Oncaea parila, Oncaea antarctica and Oncaea englishi. In November the differences in the species distribution between the two regions were less pronounced and the abundances of all species were much lower than earlier in the year. The dominant species were Oithona similis, which reached abundances of up to 182/m³ in February, and Oncaea curvata with up to 215/m³. Deeper living species were comparatively rare. Oithona similis occurred mainly in the top 200 m during both seasons. The other species, by contrast, were generally deeper and more dispersed through the water column in late winter than in summer.     

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.     

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.     

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.