Biotic effects during the settlement process of non-indigenous species in marine benthic communities

Biotic interactions, particularly predation/grazing and competition, are key factors limiting the introduction success of nonindigenous species (NIS). In addition, positive interactions are considered important drivers of community structure, and both positive and negative interactions between native and NIS can determine the ability of communities to resist MS invasions. This study was conducted in Madeira Island (NE Atlantic) to evaluate how predation and facilitation will affect settlement success of NIS. We manipulated the access of predators to bare and partially pre-invaded PVC settling plates to later be exposed to high propagule pressure of NIS in a marina environment. Results indicate that NIS diversity was greater in pre-invaded treatments, but only on those plates exposed to predators. Our findings suggest that positive interactions between established MS and incoming settlers may promote the establishment success of newcomer NIS under predation pressure.