Assessing the effect of the alien seaweed Caulerpa cylindracea on infralittoral rocky benthic invertebrate community: Evidence from a Mediterranean Marine Protected Area

Since the end of the last century, the number of new macrophytic algae introduced in the Mediterranean basin is steadily increasing. Among them, Caulerpa cylindracea is now locally established, and considered invasive. In this study, we hypothesized that the presence of C. cylindracea on hard substrates may influence macrozoobenthos communities; to test it we used a multivariate model to compare several samples from the Pelagie Islands MPA (Lampedusa, Italy) in which the alien alga was present. Samples were collected in two sites in November 2013 by scuba divers using a standard airlift sampling device and by scraping macrobenthic species. Statistical analysis highlighted that C. cylindracea was the only algal species affecting significantly the macrozoobenthos communities. Our analyses also show that the taxonomic groups Amphipoda, Caridea, Tanaidacea are related with higher presence of C. cylindracea, while Sipuncula, Nematoda and Polychaeta are correlated with native algae. We conclude that C. cylindracea attracts this benthic fauna by creating an extension of both trophic and edaphic niches. Moreover, the study shows that C. cylindracea affects the diversity of the macrozoobenthos at a state of dispersion dynamics where the alga is intermixed with other algae and not when it is dominant.