Coastal fish assemblages associated with rocky substrates: differences between a marine reserve (Pianosa island) and an unprotected area (Elba island).

Along the coastline of Italy, there are many areas of high environmental value. Nevertheless, only for few of these the protection proposed in 1982 by low has been really enforced. Understanding if marine reserves work, requires two levels of analysis. The first requires that particular reserves be evaluated in the context of the goals inherent in their establishment. The second level of analysis should be a broad comparison across reserves in different ecosystems to understand if reserves in general have a local or regional effect. Fish assemblage inside the MPAs, usually include many species targeted by fishing, so that they are primarily expected to benefit from protection, especially those having no-take reserve. The evaluation of the benefits, in terms of increase in density and size of target fishes can be useful to assess the ecological effectiveness of reserves. Up to now, there are very few long-term series of density estimates in and around MPAs before and after protection to verify these assumptions in the context of protected populations. Fish fauna distributions patterns can be useful for testing the effectiveness of habitat protection in marine reserves. Most target fishes are high-levels predator and their functional extinction may cause community wide changes. The impact of fishing has consequent top-down perturbations in marine communities structures and organization. Benthic communities in the shallow Mediterranean rocky sublittoral have 2 extreme alternative succession endpoints: coralline barrens and complex macroalgal beds. In the Mediterranean, Paracentrotus lividus is a key species that a high densities influences the dynamics of the phytobenthos, by eliminating erect algae and seagrasses, and inducing the formations of coralline barrens. Despite ecologists’ increasing interest in fish fauna living in marine protected areas, fish assemblage of some Italian marine reserves are still completely unknown. Pianosa represents the ideal area where to verify the hypothesis that are the subject of this PhD. The PhD thesis is aimed at: 1- determine the structure of the infalittoral fish assemblage inhabiting the protected (Pianosa Island) and adjacent (Elba Island) non protected areas of Tuscan Archipelago, in terms of species composition, diversity and relative density, assessing differences in the community parameters in different areas; 2- to estimate the fish community responses to the trophic cascades in shallow rocky shores as possible results that indicate the reserve effect. In infralittoral area, is possible to assess that structure of rocky fish assemblage testing the effectiveness of habitat protection in MPAs? Underwater Visual Census (UVC) is choised as the more appropriate method to conduct study on infralittoral fish community in Pianosa and Elba islands. Abundance data were collected by using a scale based on a geometric progression factor which was approximately 2. Fish density was calculated by considering the mid point of each abundant class. The size of individual fish was assigned to one of four size classes. Extensions of barren cover, was visually estimated as relative percentage by means of square of 1 m-2 located on the bottom. P. lividus was chosen as indicator liable to possible shift from macroalgal cover to barren. During the survey the degree of exploitation on fish species at Elba island, was evaluated on the basis of direct observation of fishing landings in Marina di Campo harbour. A one way ANOVA was performed to test for differences among the areas in the assemblage parameters. Permanova was performed to test differences in analysis fish community using locality as fixed factor. The reserve effect (response ratio, R), was calculated for trophic categories and exploitation levels, as ln of ratio between value of response variable (density) inside the protected area and in fished areas. During this study, 46 fish species were identified. Labridae and Sparidae were the most relevant families in relation to species richness. Some large sized specimens, belonging to species of high commercial value (i.e. Seriola dumerilili, Dentex dentex, and Ephinephelus marginatus), were also observed. Taxonomic composition of fish community in Pianosa and Elba islands agrees with other similar northern-western in Mediterranean. The abundance of target species correlates strongly with the reserve effect, and therefore shows that the reserve has been effective in providing protection for such species. Some highly spearfished species such as E. marginatus, S. umbra, or D. dentex, have been censed exclusively within the reserve. Other such as Sparus aurata are far more abundant in the reserve. Species diversity index, and Evenness, show significant differences between sites located in Pianosa. Here, Diplodus vulgaris and Diplodus sargus, showed higher abundance in protected than in unprotected area. The study of four size classes of some target species has confirmed that large individuals were significantly more abundant in the protected area. The increase of the size of fishes is a phenomenon widely reported in other MPAs and this general pattern has primarily attributed to the lack of fishing impact. Protected area seems to have the potential to restore depleted fish stocks. The response ratio evaluated for exploitation level shows that the reserve has been effective in protection for heavily fished species. Protected area, support greater density of D. sargus and D. vulgaris as predators on sea urchin P. lividus, than unprotected area. At the same time, the cover of barrens was significantly higher in unprotected area than in Pianosa. This study has evidenced a reserve effect or refuge effect characterized by the presence of large individuals. This refuge effect, within the presence of large individuals and species vulnerable to fishing, is one of the characteristics described in the definition of reserve effect. The results of the present study suggest that the recovery of Diplodus species in Pianosa seems to reestablish predatory control upon P. lividus similar to what is observed in other temperate regions and in other Mediterranean protected areas. The results of this study can corroborate the hypothesis of a transition from macroalgal beds, which harbour hundred of species of algae and invertebrates, to barrens through sea urchins grazing.In protected area, the effect of predator density on prey and on its population parameter is density-mediated indirect interactions (DMIIs). This study, is a further step toward a better knowledge of the rocky reef fish assemblage of this area. At the community level, the present study will provide a useful reference point for planning future investigations on inter-specific relationship such as competition. Pianosa is an protected area where is possible to demonstrate that reserves aimed at restoring whole assemblages and ecological processes should be established as permanent no take area. This studies confirms that besides direct effects on target species, fishing may cause changes in trophic relations and in ecosystem functioning. Despite Pianosa is not a typical MPA since actual permanent presence of penal institute, it represent an important site where to study isolated infralittoral fish community on rocky substrata. It is clear that future experiments testing the reserve effect on fish biodiversity will have to take into account the necessity of being repeated on larger spatial and temporal scales.