The biotic resistance role of fish predation in fouling communities

Predation may often influence native species dynamics and so may be important for the control of introduced species as well. Here, we examine how predation can regulate fouling communities on artificial substrates in the coast of Brazil. Specifically, we tested whether predators limit colonization and establishment of introduced species. A predation experiment using plastic plates as experimental replicates (predator excluded and not excluded) was carried out in Ceará, Bahia, São Paulo and Santa Catarina, between 3°S and 27°S. Ninety-eight species colonized the plates, 14 of which were introduced. While species richness was similar among the treatments (except in Santa Catarina), community structure varied by treatment and introduced species were less abundant in the predation treatment at all sites. Also, predation was selective and controlled introduced, poorly defended, species, specifically ascidians. Thus, biotic resistance driven by predation was not ubiquitous but apparently targets one group of major economic and environmental impact. As a consequence, introduced barnacles were released from competition with dominant ascidians and thus the ecosystem service (biotic resistance) performed by fish alone was unable to completely avoid or control the introduction of non-native species. Control measures must rely on various approaches, but if we want fish to contribute in this control, it is very important to conserve the local native assembly of predators in order to reap their benefits in this ecosystem service.