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

Abstract

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.