Abundance and distribution of non-indigenous Calyptraeidae gastropods along north and central Atlantic shores of Portugal

Two non-indigenous species of slipper limpets (Gastropoda: Calyptraeidae) have been recorded in NW Europe: Crepidula fornicata and Crepipatella dilatata. Although the former is widespread distributed in European Atlantic, records on Portuguese coasts are scarce. Regarding C. dilatata, it has been only reported in the southern Galician Rias (NW Spain). In this study, C. dilatata is reported for first time on Portugal and the distribution of these two species were studied in the North and Centre of Portugal. Moreover, abundance, distribution and structure of C. dilatata populations were compared between two intertidal habitats. Abundance and structure of C. dilatata populations showed no significant differences between habitats, suggesting that the species is well established in both. Regarding size-frequencies, bigger individuals were more frequent in soft bottoms. The recent development of oyster aquaculture in Portugal and the variety of substrates in which these NIS have been found could facilitate future introductions in nearby locations.