Comparative Survey of Anthozoan Assemblages from the Lange Anna Intertidal Zone and the Tiefe Rinne Subtidal Trench, Helgoland

Anthropogenic pressures and climate change continue to shape the biodiversity of Helgoland and the surrounding southern North Sea. To assess current anthozoan diversity and compare it with historical records, we surveyed two contrasting habitats: the intertidal rocky shore at Lange Anna and the offshore trench “Tiefe Rinne.” Intertidal sampling of Laminaria holdfasts revealed four actinian species: Cylista elegans, Sagartia lacerata, Diadumene cincta, and Actinothoe sphyrodeta. Colonization intensity showed a strong positive correlation with holdfast width and stipe thickness, suggesting that structural habitat complexity promotes anemone abundance. Subtidal dredge material from the Tiefe Rinne contained solitary actinians and colonies of Alcyonium digitatum. The widespread occurrence of the non-native D. cincta indicates ongoing faunal shifts likely linked to anthropogenic activity and species introductions. Comparison with surveys spanning nearly a century suggests both persistence (Alcyonium digitatum, Sagartia lacerata) and turnover in local anthozoan assemblages. Although limited in scope, this study highlights continuing ecological change around Helgoland and emphasizes the importance of expanded, molecularly informed monitoring of benthic cnidarian diversity.