The flow of non-indigenous species continues in the north Adriatic Sea: Cerastoderma edule and Mytilopsis leucophaeata (Mollusca: Bivalvia) are invading the Sacca di Goro lagoon

The spread of non-indigenous species (NIS) is a major threat to native biodiversity worldwide. The Mediterranean Sea is particularly affected by such a phenomenon, with high introduction rates and harmful consequences on its biota and ecosystems. Based on an integrative taxonomic approach, we hereby report the widespread occurrence of two NIS bivalves (Cerastoderma edule and Mytilopsis leucophaeata) in the Sacca di Goro Lagoon (Italy, north Adriatic Sea). The record of the former species is the first for Italy and the Mediterranean Sea sensu stricto, and also accounts for the first confirmed evidence of this species invading new areas worldwide, whilst that of the latter potentially clarifies the taxonomic uncertainties regarding the species that has invaded the north Adriatic until 2008. Although there are no certainties regarding their introduction pathways, C. edule was most likely introduced with seeding activities together with clam larvae or juveniles, while M. leucophaeata may have arrived through natural currents from nearby populations or amidst fouling communities of natural/anthropogenic floating objects or recreational vessels. Finally, although the local impact of these two new NIS is still unpredictable, C. edule can achieve extraordinarily high densities and has a structural role as a habitat engineer, influencing the distribution of surface sediments, while M. leucophaeata can foul and clog anthropogenic substrates and outgrow and replace benthic species. A careful monitoring of the area during the next years is therefore necessary to evaluate the consequences of these new introductions.