Arrivals and departures: exploring sea slug diversity (Mollusca, Gastropoda) in the Salento Peninsula harbours

This study investigates the Heterobranchia species present in the harbours of the Salento Peninsula, in southern Italy, in the central Mediterranean Sea. A total of 158 specimens from 21 families and 54 species were recorded from 2020 to 2025, including five non-indigenous species (NIS): Anteaeolidiella lurana, Bermudella polycerelloides, Camachoaglaja africana, Polycera hedgpethi and Stiliger cf. auarita. Among the total 54 Heterobranchia species, one is a new record for the Mediterranean Sea; five are new records for the Ionian and/or Adriatic Seas; and 12 species are added to the Salento Peninsula fauna. The finding of about one-third of the total number of species known for the Salento Peninsula, from ports and marinas is noteworthy and emphasizes the need for continuous monitoring of areas under anthropological stress for early warning of NIS and of neglected endemic diversity. The methodology used to collect heterobranchs in these restricted access habitats revealed to be powerful and effective to unravel small and difficult-to-see organisms such as most of the species here recorded. This research contributes to expanding the knowledge of marine Heterobranchia biodiversity enhancing the known Mediterranean diversity and shedding light on anthropized and poorly known environments such as harbours and marinas.