Blue mussel Mytilus edulis as habitat provider on offshore wind turbine foundations

We compare the species composition of the early (mussels not prevalent) and mature (mussels prevalent) subtidal colonizing communities at offshore windturbine foundations with special attention to the mobility and habitat preferences of the colonizing species. We identified 47 species belonging to nine different phyla from the samples of the mature community, including 21 species unique to the secondary substratum provided by the mussel shell, all of them are sessile species. Only 17 of the 37 species identified from the early subtidal colonizing community were present in the mature community. The main phyla present in both the early and mature samples were Mollusca, Arthropoda, and Annelida. Our findings confirm the hypothesis that mussels counteract the impoverishment of total species richness on wind turbines, caused by the abundant presence of Metridium senile in mature artificial hard substratum communities by providing secondary substratum for colonization by. sessile and hemi-sessile epifauna. The species assemblage found on these mussels is different from the one previously found on the piles, and only seventeen species (~36%) present in the mature community were already present in the first year after installation. In 2020, all bryozoan species (7) were exclusively observed on the secondary substratum provided by the shells of the mussels. However, these species were previously encountered on the scour protection or on the shells of other bivalves. This may be due to the fact that the secondary substratum provided by the mussels differs in physical properties (e.g., microhabitat complexity) from the primary (vertical) substratum of the pile.

RBINS Publication(s), Open Access