Habitat availability determines distribution patterns of spionid polychaetes (Annelida: Spionidae) around Tokyo Bay

An investigation of the distribution and habitat utilization of spionid polychaetes in Tokyo Bay revealed eight shellboring and 18 non-boring (interstitial, epifaunal, and infaunal) species, of these 11 species were recorded in the area for the first time. Most of the boring and interstitial species, which are associated with mollusc shells, were mainly distributed in exposed environments favoured by their host species outside Tokyo Bay. Only two boring species, Polydora websteri and Polydora haswelli preferred the enclosed waters of Tokyo Bay. Epifaunal and infaunal species were mainly distributed in the sandy and/or muddy sediment within Tokyo Bay. A widespread or localized distribution pattern within species was observed corresponding to the larval developmental mode. We concluded that habitat availability determines distribution patterns of spionid polychaetes around Tokyo Bay. Novel habitats for Boccardiella hamata, Boccardia proboscidea, Carazziella spongilla, and Polydora cornuta were recorded. Boccardia pseudonatrix, which was recorded for the first time from Japan with clear locality information, is considered to be a potential alien species.