PLURIANNUAL ANALYSIS OF THE RESERVE EFFECT ON ICHTHYOFAUNA IN THE SCANDOLA NATURAL RESERVE (CORSICA, NORTHWESTERN MEDITERRANEAN)

From July 1988 to September 1992, Scuba divers used a non-destructive sampling method to study the fish communities of rocks and Posidonia o ceanica seagrass beds, in Scandola Marine Reserve. Sites were establis hed in the integral reserve (protection of the marine environment), in the non-integral reserve (partial protection) and outside the reserve (no protection). Average density and biomass of the sampled populatio n in P. oceanica seagrass beds showed no significant difference betwee n the sites in the integral reserve and the others. Only the integrall y-protected shallow and deep water zones showed considerably reduced s easonal variations. For rocky substrata, the integral reserve site dem onstrated higher density and biomass than the other sites. The impact of seasonal variations on the sampled population was not reduced in th is biotope, as in the seagrass beds. Whatever the biotope, the demogra phic structures of the fish population sampled in the integral reserve and in the other sites were different: the number of large fishes (ma tured adults) was always the highest. Species diversity was slightly g reater in the seagrass bed sites of the integral reserve, but site var iations were not significant. This was also true for rocky substrata; in contrast, lesser seasonal differences were recorded in the integral reserve than outside. Three conclusions can be drawn from these pluri annual observations: 1) The reserve effect is real, not just theoretic al, and affects the fish population in both rocks and seagrass beds. 2 ) The two sites studied, the Posidonia oceanica seagrass beds and rock y substrata, react very differently to protection which reduces anthro pogenic disturbances. These differences may be attributed to the degre e of sensitivity of the dominant families (Labridae in the seagrass, S paridae in rocky substrata) to all disturbances. 3) The reserve effect comprises both a refuge and a buffer effect. The refuge effect is the most traditionally highlighted and is characterized by more large fis hes and a greater variety of species and noble fishes (Dicentrarchus l abrax, Sparus aurata, Epinephelus marginatus, Sciaena umbra). The buff er effect, never shown in previous studies, is characterized by the fa ct that the impact of seasonal variations on parameters such as densit y, biomass, and diversity is considerably lessened.