Marenzelleria viridis (Verril, 1873) (Polychaeta: Spionidae) : a new record from the Ems Estuary (The Netherlands / Federal Republic of Germany)

A new record of the North American spionid polychaete Marenzelleria viridis (Verril, 1873) is reported from the Ems Estuary. The species was first found in 1983. From 1983 to 1986 densities increased to a few thousands per m2 while densities of another polychaete, Nereis diversicolor decreased. Juveniles showed peak densities of c. 19000 m2 in muddy sediments. Adults preferred sandy sediments. In Europe M. viridis was recorded recently also in other estuaries: Tay and Forth (Scotland), Weser and Elbe (Fed. Rep. of Germany). There is no reliable clue to the cause of its appearance in North Sea estuaries