ZOOBENTHIC SUCCESSION IN BALTIC SEDIMENTARY HABITATS

The successional stages of Baltic Sea zoobenthos were analysed along a south/north transect (Belt Sea, northern Danish straits to the Bothni an Sea) in relation to a proposed conceptual model of succession. The model predicts five successional stages ranging from diverse communiti es to dead bottoms. Stage I: 'climax community' dominated by deep-burr owing species, and a deep RPD-layer, II: first signs of stress, strong fluctuations, decreasing species richness, increased biomass/producti on, and an elevated RPD-layer, III: dominated by small polychaete worm s (or their ecological equivalents), and the RPD-layer close to the se diment/water boundary layer, periods of hypoxia, IV: long periods of h ypoxia and formation of bacterial mars (Beggiatoa spp.) at the sedimen t surface, no permanent benthic macrofauna, V: complete break-down of benthic communities due to long-term anoxia, lamination of sediments. Differences in successional sequences between basins and vertical zone s (supra- and sub-halocline) are documented, and general trends are di scussed in relation to changes on a geological time-scale.