Biodiversity Survey of Opisthobranch Species near Helgoland, Germany

Opisthobranchia is an informal group of mostly marine gastropods that includes snails and slugs with reduced or absent shells. This study investigated opisthobranch species diversity around the German island of Helgoland, located approximately 50 km offshore in the southeastern North Sea, to characterize their distribution across different marine habitats. A total of ten species were identified: eight from the Tiefe Rinne (a deep channel in the German Bight), one from the rocky intertidal, and one from a plankton tow. Atalodoris pusilla and Candiella plebeia were the most abundant species. The higher species richness recorded in the Tiefe Rinne highlights its role as a local biodiversity hotspot. However, due to the limited sampling effort and the small, cryptic nature of many opisthobranchs, additional species likely occur but were not detected. These findings provide preliminary baseline data on opisthobranch diversity around Helgoland and indicate the need for more extensive surveys to better understand their distribution.