POPULATION-DYNAMICS OF MAGELLANIA-FRAGILIS, A BRACHIOPOD DOMINATING AMIXED-BOTTOM MACROBENTHIC ASSEMBLAGE ON THE ANTARCTIC SHELF

A dense assemblage of the brachiopod Magellania fragilis was sampled b y trawl and underwater photography during the expedition ANT IX/3 (199 1) of RV 'Polarstern' on the shelf of the Lazarev Sea, Antarctica. Mea n abundance and biomass estimates for M. fragilis were 26.15 individua ls 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 -(0.020 (t+1.326)))(0.828) described these data best. The annual somat ic PIE 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 in dicate that M. fragilis is a comparatively slow-growing species with v ery low annual productivity.