SUCCESSFUL ESTABLISHMENT OF THE SPIONID POLYCHAETE, MARENZELLERIA-VIRIDIS (VERRILL, 1873), IN THE DARSS-ZINGST ESTUARY (SOUTHERN BALTIC) AND ITS INFLUENCE ON THE INDIGENOUS MACROZOOBENTHOS

Marenzelleria viridis (Verrill, 1873), a North American spionid polych aete that immigrated to brackish water ecosystems of the North Sea and Baltic Sea in the early eighties, has spread rapidly in its European biotopes and is now a dominant element of the fauna in some regions. I t was first found in the Darss-Zingst bodden chain, an estuary on the southern Baltic coast, in 1985. Continuous monitoring from 1991 to 199 4 showed that M. viridis has continuously spread in these waters and h as revealed the effects of its introduction on the indigenous fauna. T he highest abundances and biomasses (about 30,000 ind.. m(-2) and 400 g wet weight . m(-2)) were found in the inner pan of the estuary (S = 3-5 PSU). Significant positive correlations (abundance and rank correl ations) existed between the adult and juvenile subpopulations of M. vi ridis and between juvenile M., viridis and chironomids (Larvae of the Chironomus plumosus and Ch. halophilus types). Negative correlations w ere found between the spionid and both Corophium volutator and the nai dids. The abundance and biomass data collected for various macrozooben thos representatives (Hediste diversicolor, Corophium volutator, Hydro bia spp., chironomids and oligochaetes) during the present study are c ompared with those available in the literature to assess the impact of the new species.