The effects of recreational Paracentrotus lividus fishing on distribution patterns of sea urchins at Ustica Island MPA (Western Mediterranean, Italy).

This study evaluated the effects of recreational Paracentrotus lividus fishing on average density and size of this edible sea urchin, and its indirect effects on Arbacia lixula on barren substrates of Ustica Island MPA (SW Italy, Mediterranean Sea). Size, single and pooled species densities, density of large individuals (>40mm long) and small individuals (<20mm long) of the two species were estimated by scuba diving in autumn 2003, spring and summer 2004 at two sites impacted by P. lividus fishing (Punta Cavazzi and Pagliaro, take zone C) and one control (Cala Sidoti, no take zone). Two samplings were performed in each season.We found that reduced densities of P. lividus and A. lixula occurred at the fished sites compared with the unfished sites. P. lividus was always larger and more abundant at the protected site than the fished ones, whereas A. lixula had a larger density at the protected site and greater size at the fished sites. The significantly lower density of A. lixula at the sites subjected to fishing of P. lividus could suggest that A. lixula did not benefit from this kind of fishing and thus the two sea urchins might partially share the same habitat and resources in the barren habitats of “Ustica Island” MPA. These outcomes emphasize the role of regulated fishing in maintaining urchin populations at such low densities that interspecific competition is not induced.