Invertebrate associations with gastropod shells inhabited by Pagurus­bernhardus (Paguridae) – secondary hard substrate increasing biodiversity­in North Sea soft‐bottom communities

Abstract

The crustacean Pagurus bernhardus is an abundant hermit crab species in the soft‐bottom benthic communities of the North Sea. The gastropod shells inhabited by the hermit crab were found to provide substrate for a diverse epizoic fauna. In order to describe the epizoan community as well as spatial differences in epizoan communities of the North Sea, hermit crabs were sampled during summer 2001 at five stations in the North Sea. In total, 51 epizoic species with up to 15 species and 427 individuals per crab were found. The most abundant epizoans were obligate associated species such as the polychaete Circeis amoricani paguri, the cnidaria Hydractinia echinata and the crustacean Trypetesa lampas, as well as sessile epizoans also found in hard‐bottom habitats such as balanids Balanus crenatus and Verruca stroemia or free‐living species such as the amphipod Gammaropsis nitida. The epizoic community structure on shells of the stations north of the 50 m contour differs from the southern communities on the Dogger Bank and in the German Bight. The northern stations were dominated by sessile species, whereas a higher proportion of free‐living epizoans occurred at the southern stations. The results are discussed concerning the ecological importance of shells inhabited by hermit crabs as a hard substrate in soft‐bottom habitats.