BLACK SPOTS PRODUCED BY BURIED MACROALGAE IN INTERTIDAL SANDY SEDIMENTS OF THE WADDEN SEA - EFFECTS ON THE MEIOBENTHOS

The effects of buried decaying macroalgae on meiobenthos were examined in intertidal sandy sediments of the Wadden Sea of Lower Saxony. In s itu experiments confirmed that one of the principal causes of the form ation of reduced surface sediments or 'black spots' on the tidal flats is the increasing occurrence and subsequent decomposition of filament ous green algae (Enteromorpha spp.) buried in the sediment. Five to fi fteen days after algal material had been buried, the sediment surface turned black. The impact of these black spots on meiobenthos was drama tic: the changed chemical conditions in the sediment resulted in long and drastic reductions in meiofaunal abundance and number of taxa. A m ulti-dimensional scaling (MDS) analysis of data on meiobenthic abundan ces revealed that samples from black-spot areas were clearly separated from those of control and reference areas. Re-oxidized black spots sh owed recolonization by meiofaunal animals, with numbers of individuals and taxa similar to those of oxidized surface sediments. The use of a bundances of members of higher meiobenthic taxa to monitor changes in the sediment's chemistry, especially those caused by biomass overload, is discussed.