Spatial and temporal distribution of macrofauna in the Otzumer Balje (East Frisian Wadden Sea, Germany)

The spatial and temporal distribution of the macrofauna in a subtidal area of the East Frisian Wadden Sea (Otzumer Balje) was investigated. Grab samples were taken at 30 stations covering the whole tidal inlet area. Focusing on the seasonal variability sampling was carried out in March and September 1998 using a 0.1 m(2) van Veen grab. During the survey, a total of 108 macrobenthic species was recorded, dominated by polychaetes and crustaceans contributing 47 and 36 species, respectively. Highest mean species numbers and abundances were found in the deeper central inshore parts of the channel, whereas the lowest were found in the highly dynamic inlet region. With a mean of 3.2 g AFDW/m(2) the biomass of the subtidal macrofauna was relatively low compared to the intertidal fauna. Multivariate data analysis (MDS and clusteranalysis) showed three distinct faunal assemblages: (1) a community in the inlet region on sandy sediments characterized by Spio martinensis, Scoloplos armiger, Bathyporeia pelagica and, additionally, in September by the polychaetes Magelona johnstoni and Scolelepis squamata; (2) a community in the shallow and deep inshore channels on muddy sediments dominated by Tubtficoides benedem, Heteromastus filiformis and Tharyx killariensis; and (3) an 'intermediate community' in shallower regions of the tidal channel and smaller gullies on muddy sands characterized by Spio martinensis, Tubificoides benedem, Scoloplos armiger and Tharyx killariensis. The seasonal spatial community structure was more or less stable, whereas the seasonal variability in the species composition within the communities was high, due to recruitment and import processes during the summer. The community structure is discussed in terms of ecosystem properties such as sediment composition and hydrography.