Meroplankton distribution in the central Barents Sea in relation to local oceanographic patterns

Abundance and spatio-temporal distribution of meroplankton (larvae of invertebrate benthos) in the central Barents Sea and their dependence on abiotic factors were investigated. Samples were taken in different depth intervals on a south-north transect in the marginal ice zone in May 1997. At several locations sampling was repeated in June 1997. In May, total meroplankton abundances varied between 0.1 ind. m^-3 and 32.0 ind. m^-3, but mainly fluctuated around 10-15 ind. m^-3. They were strongly affected by the mass occurrence of single species. At the northern, heavily ice-covered stations numbers decreased significantly. Larvae of 27 types were found. Polychaetes represented the most diverse group (13 species), followed by echinoderms (8 species). Larvae of only one bivalve species were found (Mya truncata), but with very high abundances (86 ind. m^-3). Other taxa were represented only by single specimens. In June, total abundances were similar. The same species were present but the distribution patterns were less distinct, diversity values were higher and most larvae were further developed than in May. Distribution patterns of the larvae were to a large extent determined by physical processes in the area of the Polar Front, which acted as a distinct barrier in surface waters. In May, four meroplankton assemblages were distinguished, each associated with a different water mass. Most of the larvae have also been found in other investigated Arctic areas and belong to species with an Atlantic-Boreal-Arctic or Boreal-Arctic distribution. The relatively high numbers of larval types found in this study indicate that indirect development with pelagic larval stages plays a role in benthic recruitment in this sub-Arctic region. The relevance of these observations for the so-called Thorson rule is discussed.