BIOMASS AND ABUNDANCE OF MACROFAUNA IN INTERTIDAL SEDIMENTS OF KONIGSHAFEN IN THE NORTHERN WADDEN SEA

Intertidal sediments of Konigshafen (Island of Sylt, North Sea) were sieved for mesofauna (> 0.25 mm) and macrofauna (> 1 mm) in spring and autumn 1990. Although sediments are coarser than in other parts of the Wadden Sea, the macrobenthic fauna was very similar but with a tendency towards higher species density, abundance and biomass. Taking info account the areal size of sandy flats, seagrass beds, mud fiats and mussel beds, the average biomass is calculated to be 65 g ash-free dry weight m(-2). The lugworm Arenicola marina dominates the biomass (28%), followed by the bivalves Mytilus edulis (21%), Mya arenaria (16%), Cerastoderma edule (10%) and the mudsnail Hydrobia ulvae (9%). While spring and autumn biomass are almost alike, abundance is highly variable and entirely dominated by H. ulvae. Mesofauna is mainly composed of oligochaetes, small and juvenile polychaetes. Abundance is similar to that of macrofauna, while biomass is only about 1 g m(-2). Macrophyte biomass amounted to 9% of that of macrofauna. In the course of the century, mussel beds expanded while muddy areas declined. The concomitant effects on biomass presumably compensated each other.