Abstract
The colonization of the underwater construction of an offshore research platform in the German Bight by Mytilus edulis was investigated. Mussel abundance, biomass and percentage coverage of the construction were determined from summer 2003 to summer 2005 from different water depths using digital underwater images and scrape samples of the hard substrate fauna. Growth was estimated from shell length distributions. In 2003 settlement of M. edulis was low at the platform mainly due to a temporal mismatch between platform construction and occurrence of competent larvae. In summer 2004 mussel abundance increased remarkably in the intertidal and upper subtidal. Abundance and biomass increased up to 30,000 individuals m-2 and approximately 40 kg m-2 in summer 2005. At the end of the investigation period, the upper part of the platform foundation was completely covered by M. edulis. Lower parts remained sparsely colonized. Mussel growth rates were high under offshore conditions because of favourable environmental conditions and reduced biological constraints. Cumulative effects from wind farm entities are estimated. Mussel accumulations will be an important component in the estimation of ecological implications of offshore wind farming at least at the local scale.