The role of the hydroid Eudendrium racemosum (Cavolini, 1785) (Cnidaria: Hydrozoa) as basibiont for exotic species in marinas

Effective management of non-indigenous species (NIS) in marinas requires accurate knowledge of their biodiversity. A temporal study of macrofaunal assemblages associated to the native arborescent hydroid Eudendrium racemosum was conducted in two marinas with intense maritime traffic on the Spanish Atlantic and Mediterranean coasts. While only 7 (all peracarid crustaceans) of the 52 species were NIS, they frequently dominated macrofaunal assemblages in abundance. Factors affecting these assemblages were primarily hydroid density and water turbidity, and secondarily water salinity and temperature. The relative contribution of NIS to the community, both in number of species and abundance, was significantly higher in Palma (Mediterranean) than in Cádiz (Atlantic) during the entire year. The structure of the total and NIS community also differed between marinas, highlighting the local singularity of these human-made environments. Despite the lack of basibiont specificity of most exotic epibionts, E. racemosum seems to facilitate the proliferation of the exotic amphipod Paracaprella pusilla compared with other hosts, probably due to mutualistic relationships. • Macrofauna associated with Eudendrium racemosum differed between marinas. • Seven species of 52 were exotic, all peracarid crustaceans. • Exotic species dominated macrofaunal assemblages in terms of abundance. • Hydroid density and water turbidity modulated macrofaunal assemblages. • Despite the lack of basibiont specificity, E. racemosum facilitated the proliferation of P. pusilla .