The first record of the Lessepsian sacoglossan <i>Elysia</i> sp.2 from the Aegean Sea, with discussion of its taxonomy and habitat preferences

Native to the Indo-Pacific region, the sacoglossan species complex Elysia cf. marginata-grandifolia is considered a Lessepsian migrant and an alien species in the Mediterranean Sea, following its first record along the coast of Turkey in 2001, and consecutive observations in the area. Subsequent studies have reported its presence in the Levantine basin along the coasts of Turkey, Israel, Lebanon, and Cyprus, with uncertainties around its taxonomic assignment. This paper highlights the presence of two alien Elysia species included in these reports, separated now for the first time. We also present new findings of Elysia sp. 2’s range, marking its first occurrence in the Aegean Sea in July 2024 along the coast of Lipsi Island, Greece. This record represents the species’ westernmost distribution in the Mediterranean basin, highlighting a potential ongoing range expansion. Although further examinations in the region would be needed to fully ascertain whether an established population is present in the Aegean Sea, this report demonstrates the importance of continuous monitoring in the early detection of the presence of alien and invasive species, to inform conservation and management strategies.