Native predators control the population of an invasive crab in no-take marine protected areas.
The resistance of an ecosystem to species invasion is considered to be related to the abundance and diversity of native species (i.e. biotic resistance hypothesis). Theory predicts that the high native diversity in pristine systems can hinder the establishment and/or the spread of non-native species through direct and indirect mechanisms (e.g. through competitive and/or predatory interactions). Here we tested whether predation provides higher resistance to invasion by the Percnidae crab Percnon gibbesi (H. Milne Edwards, 1853) in protected native communities, compared with exploited ones. Specifically, this study aimed to compare: (i) the abundance and diversity of potential predator assemblages of P. gibbesi; (ii) the predation pressure on P. gibbesi; and (iii) the density of this species in two protected and two unprotected sites along the northern Sicilian coast (Italy). The relative predation rate was assessed by manipulative tethering experiments conducted on two size classes of P. gibbesi using long and short tethers, both at protected and unprotected sites. The abundance and diversity of the predators of P. gibbesi and the relative predation rate on tethered crabs were higher at protected than at unprotected sites, independent of crab size and tether length. The density of P. gibbesi was significantly lower in protected compared with unprotected sites. These results suggest that the diversity and abundance of native predator assemblages directly affect the invasion success of P. gibbesi in the Mediterranean Sea. We provided experimental evidence that the restoration of predator assemblages confers 'biotic resistance' to no-take marine protected areas (MPAs) against P. gibbesi invasion. Our study confirms that no-take MPAs are effective in combating non-indigenous species (NIS) invasion, and that it is crucial to establish a long-term monitoring programme to limit the introduction of NIS and to control the spread of existing ones.