Development of Small Mytllus Beds and its Effects on Resident Intertidal Macro fauna

Abstract

Abstract. The development of temporary Mytilus edulis beds and their associated macro fauna was studied on an intertidal sand flat in the German Wadden sea during 1986 by comparing mussel beds with bare sandy areas of the same tidal elevation. Macro fauna samples We taken with a 100 cm2 corer (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 macro fauna organisms decreased with the age of the mussel bed, whereas the relative abundance of species was not strongly affected. Hydrobia ulvae, oligochaetes, and Heteromastus filiformis dominated the macro fauna inside as well as outside the mussel beds. Among the lower ranks of dominance changes in species composition were observed due to increasing densities of opportunistic polychaetes.About six weeks after the establishment of the mussel beds a higher abundance of Capitella spp., Polydora ligni, Tharyx marioni, and nemerteans occurred within the mussel beds while other species such as Hydrobia ulvae and Pygospio elegans showed a significantly lower abundance compared to the adjacent flat. Macoma balthica as well as Mya arenaria were not affected by the alteration of a bare sand flat to a mussel bed. O‐group Carcinus maenas reached their highest abundance in the mussel beds (over 1000 indiv. m‐2). In contrast juvenile Crangon crangon preferred the bare sand flat. After destruction of the mussel beds by an early autumn storm, species abundance and composition was similar to the situation before the mussel beds had become established.