Diversity and Distribution of Coiled-shelled Marine Gastropods around Helgoland

This study documents the 2025 diversity and distribution of coiled-shelled gastropods around Helgoland and compares them with records spanning 86 years. 13 species were observed, ten from the intertidal rocky shore and three from the subtidal trench “Tiefe Rinne”, contributing to a total of 31 species recorded since 1939. Most species were habitat-specific, with Littorina spp. dominating the intertidal and Steromphala tumida characterizing the trench. The assessment of the intertidal distribution of Littorina littorea and L. obtusata using rocky shore quadrat sampling showed no significant zonation along the shore but revealed opposing correlations with algal cover. L. littorea decreased with increasing algae (rho = –0.70, p = 0.0011), whereas L. obtusata increased (rho = 0.77, p = 0.00019). These results suggest that substrate type, rather than shore zone, primarily determines gastropod distribution around Helgoland, underscoring the role of habitat structure in shaping intertidal community composition.