Stefan Hain

QUANTITATIVE INVESTIGATIONS ON MACROBENTHOS COMMUNITIES OF THE SOUTHEASTERN WEDDELL SEA SHELF BASED ON MULTIBOX CORER SAMPLES.

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.

Notes on the reproduction of high-Antarctic molluscs from the Weddell Sea

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.

Macrofaunal communities on the continental shelf and slope of the southeastern Weddell Sea, Antarctica

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.

Population Dynamics Of Magellania Fragilis , a Brachiopod Dominating a Mixed-Bottom Macrobenthic Assemblage on the Antarctic Shelf

A dense assemblage of the brachiopod Magellania fragilis was sampled by trawl and underwater photography during the expedition ANT IX/3 (1991) of RV ‘Polarstern’ on the shelf of the Lazarev Sea, Antarctica. Mean abundance and biomass estimates for M. fragilis were 26.15 individuals m 2 and 1.13 g AFDM m 2 , respectively. Growth bands visible on the shell were interpreted as annual growth marks caused by the strong seasonality of food input to the benthos and were treated as size-at-age data. The von Bertalanffy growth function L t (mm) = 51.67 (1 - e 0020 (t +1.326))3.828 described these data best. The annual somatic P/B ratio was very low, 0.046 y 1 , and annual production amounted to 0.052 g AFDM m 2 y 1 at this particular site. These results indicate that M. fragilis is a comparatively slow-growing species with very low annual productivity.

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

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.

Lissarca notorcadensis (Bivalvia Philobryidae) living on Notocidaris sp (Echinoidea Cidaridae): Population dynamics in limited space

SummaryPopulation dynamics of the epizoic bivalve Lissarca notorcadensis living on spines of cidaroid sea urchins in the Weddell Sea were investigated. Total production (somatic & gonad) of the suspension feeding bivalve ranged between 16.5 and 487.4 mg AFDM y−1 per sea urchin. Annual sedimentation rates are not sufficient to maintain the production of the Lissarca sub-populations carried by the sea urchins, and resuspension of organic matter is most likely to be an important food source. The ratio of the number of freshly settled juveniles to the number of embryos brooded is between 0.054 and 0.207 and seems negatively related to the biomass already present, indicating intraspecific competition for space. Interspecific competition for space is caused by the strong preference of L. notorcadensis as well as other epizoa (colonial anthozoans and bryozoans) for the spines located on the aboral hemispere of the sea urchins.