Microbial biomass and activity in the vicinity of a mussel bed built up bythe blue mussel Mytilus edulis

Our study focuses on the impact of the biosedimentary system mussel bed (My tilus edulis) on the spatial variability of benthic microbial biomass and a ctivity in relation to organic deposits. We sampled a transect of six stati ons from the muddy mussel bed towards a reference station in the sandflat i n monthly intervals for year. The sediment grain size fraction <63 mu m and the total organic carbon (TOC) concentration decreased significantly towar ds the sandflat. Bacterial numbers and total microbial biomass (total adeny lates) showed a high spatial variability and were not correlated to increas ing distance from the mussel bed. However, a significant relationship with the TOC concentration was found. In contrast, the energetic status (adenyla te energy charge) of the microbial community in the mussel bed was signific antly lower than in the sandflat. A principal component analysis of the sub strate-utilization pattern revealed clear differences between the microbial communities in the mussel bed and in the sandflat. Our results indicate th at the sandflat may be dominated by a relatively specialized benthic microb ial community with an increased efficiency in utilizing organic carbon sour ces. As a disadvantage, however, such r-strategists are only able to meet e nvironmental changes within a comparatively narrow range. Benthic microbial communities in the vicinity of an M. edulis mussel bed, in contrast, are d ominated by relative generalists with a greater physiological capacity to b uffer discrete environmental changes. Such K-strategists show a lack of spe cialization which generally means a reduced efficiency in utilizing a parti cular resource.