DEVELOPMENT OF SMALL MYTILUS BEDS AND ITS EFFECTS ON RESIDENT INTERTIDAL MACROFAUNA

The development of temporary Mytilus edulis beds and their associated macrofauna was studied on an intertidal sandflat in the German Wadden Sea during 1986 by comparing mussel beds with bare sandy areas of the same tidal elevation. Macrofauna samples were taken with a 100 cm(2) c orer (penetration depth 27 cm, mesh size 0.5 mm, 5 parallel samples). Numbers of taxa and diversity were higher in the mussel beds compared to the sandy areas. The abundance of macrofauna organisms decreased wi th the age of the mussel bed, whereas the relative abundance of specie s was not strongly affected. Hydrobia ulvae, oligochaetes, and Heterom astus filiformis dominated the macrofauna inside as well as outside th e mussel beds. Among the lower ranks of dominance changes in species c omposition were observed due to increasing densities of opportunistic polychaetes. About six weeks after the establishment of the mussel bed s a higher abundance of Capitella spp., Polydora ligni, Tharyx marioni , and nemerteans occurred within the mussel beds while other species s uch as Hydrobia ulvae and Pygospio elegans showed a significantly lowe r abundance compared to the adjacent flat. Macoma balthica as well as Mya arenaria were not affected by the alteration of a bare sand flat t o a mussel bed. 0-group Carcinus maenas reached their highest abundanc e in the mussel beds (over 1000 indiv. . m(-2)). In contrast juvenile Crangon crangon preferred the bare sandflat. After destruction of the mussel beds by an early autumn storm, species abundance and compositio n was similar to the situation before the mussel beds had become estab lished.