Mollusk diversity of coralligenous build-ups in the southwestern Ionian Sea

The coralligenous algal reefs are priority ecosystems of the Circalittoral zone of the Mediterranean Sea shelves. Characterized by decimeter- to meter-high build-ups, these reefs create a complex environment hosting high biodiversity. Despite their common occurrence, the roles of mollusks within coralligenous structures have been overlooked until recently. To address this gap, the CRESCIBLUREEF project investigated samples of coralligenous build-ups collected from diverse settings at similar depths (33.5-37.2 m) along the SE Sicilian shelf (Italy). In the studied samples, we identified 158 mollusk species –mostly autochthonous–including some previously undocumented for this habitat. Our study underscores the importance of using appropriate sampling techniques in studying mollusk biodiversity and the pivotal role algal reefs play in supporting a diverse array of mollusk species, spanning not only those associated with hard substrates but also epiphytic, cryptic, and infaunal species. Despite the samples being sourced at similar depths, multivariate statistical analysis based on mollusk abundance indicated a distinction between coralligenous morphologies in the living assemblage. Overall, our findings contribute to improving the knowledge on mollusks associated with coralligenous reefs and emphasize the valuable role of mollusks as sensitive indicators of environmental conditions, confirming their vital importance in conservation science and benthic ecology.