Discovery of the non-indigenous bryozoan Smittoidea prolifica Osburn, 1952 near Helgoland: first record in 2011 for the German North Sea

Since 2011, the non-indigenous Pacific bryozoan Smittoidea prolifica Osburn, 1952 was observed repeatedly on shell gravel in the trench Tiefe Rinne during annual long-term monitoring assessments of subtidal sites around the island Helgoland. It is the earliest discovery for the German North Sea and three years earlier than its first detection at commercial harbour sites on the German Wadden Sea coast. Introduction to the North-East Atlantic is assumed to have occurred before 1995 with oyster transfers to The Netherlands for aquaculture purposes. The presence of S. prolifica in the natural habitat of the Tiefe Rinne, relatively distant from the main shipping routes and commercial ports in the German North Sea and without nearby mussel cultures, requires the consideration of introduction vectors other than intentional shellfish transport and international shipping traffic.