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 m2 and 1.13 g AFDM m2, 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 Lt (mm) = 51.67 (1 - e0020 (t +1.326))3.828 described these data best. The annual somatic P/B ratio was very low, 0.046 y1, and annual production amounted to 0.052 g AFDM m2 y1 at this particular site. These results indicate that M. fragilis is a comparatively slow-growing species with very low annual productivity.

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