Seasonal and bathymetric effects on macrofouling invertebrates’ primary succession in a mediterraenan non-indigenous species hotspot area

The present study investigates macrofouling development in the Mar Grande of Taranto (Central Mediterranean Sea), a wide confined area that has attracted considerable attention in recent years due to the establishment of numerous non-indigenous species (NIS). Different starting times of a yearly primary succession on artificial substrates were tracked so as to investigate the matching of the development pattern with contingency and/or convergence models, identifying NIS’s structural role in the community endpoint. Our results show that during the experiment all assemblages tended to converge towards multiple contingent communities according to starting times and depths. The differences are due to propagule availability which influence further species interactions. Thus the endpoint patterns are defined by a contingent community development determined by the seasonal species pool, their phenologies, pre- and post-settlement events, and species interactions. The most important structuring species was Mytilus galloprovincialis, which was present in almost all the endpoint assemblages, in particular when it recruits at early stages of the community development. Another abundant species at the endpoint was the alien Branchiomma boholense; which was a persistent structural component contributing to an alternative state in which Mytilus galloprovincialis loses its structural importance and where B. boholense becomes dominant, leading to an increase in fouling biodiversity of the endpoint assemblage.