Contribution to the invertebrate fauna of the islets in the Inner Ionian Sea Archipelago, Greece

Islets often host unique and fragile ecosystems, yet the invertebrate biodiversity of the Inner Ionian Sea Archipelago remains poorly documented. During a targeted expedition across ten islets between Lefkada, Kefalonia and mainland Greece, we conducted the first comprehensive survey of their terrestrial invertebrate fauna. Using hand collecting, net sweeping and substrate sieving, we recorded 222 taxa spanning multiple phyla (Arthropoda, Mollusca, Annelida). Most of these records are deemed new for the region, even though several of the taxa are regarded as well-established since they have an extended distribution in western Greece. Species richness varied substantially among islets, with Kalamos hosting the highest number of taxa (72) and the unnamed islet near Kastos the lowest (11). Multivariate analyses using selected arthropod taxa based on presence–absence data revealed several faunal clusters, although low statistical support suggests considerable heterogeneity among islets. Diversity metrics indicated that Alafonisi exhibited the greatest taxonomic distinctness, whereas Mermygkas showed the most homogeneous fauna. Several endemic and regionally significant species were detected, including multiple Ionian endemics and taxa newly recorded for the archipelago. The results highlight the conservation importance of these small landmasses, which harbour distinct assemblages shaped by isolation, geomorphology, human activity and potential species transfers via boats or grazing animals. This study provides a foundational dataset for future biogeographical, ecological and taxonomic research in the Ionian region and underscores the value of islets as natural laboratories of biodiversity. Finally, the study provides the first standardised Darwin Core dataset for the region, establishing a foundational resource for future ecological, taxonomic, and biogeographical research.