Distribution of gelatinous macrozooplankton in the southern Black Sea during 1996-1999

In this study, spatial and temporal distributions of three gelatinous macro zooplankton, the scyphozoan Aurelia aurita and the ctenophores Pleurobrachi a pileus and Mnemiopsis leidyi, were evaluated using the data obtained from seven southern Black Sea cruises carried out from 1996 to 1999. A comparis on of nets used for the sampling of gelatinous macrozooplankton illustrated the superiority of the Hensen net with a larger mesh size (300 mum) over t he Nansen net (112 mum). P. pileus was mainly concentrated below the mixed layer, while A. aurita and M. leidyi were generally confined to surface wat ers. Horizontally, P. pileus was associated with deep, offshore waters. P. pileus also displayed the least interannual variation of the three species. Biomass of A. aurita and M. leidyi varied substantially seasonally and int er-annually. In September 1999, the average biomass of M. leidyi was at its lowest level (12 g wet weight m(-2)) since its explosive development at th e end of the 1980s. This was associated with the appearance of the new pred atory ctenophore Beroe ovata, which appeared in the Black Sea at the end of the 1990s.