Surviving at the edge of a fragmented range: patterns of genetic diversity in isolated populations of the endangered giant Mediterranean limpet (Patella ferruginea)

The survival of endangered and rare species with slow growth and low dispersal capabilities critically depends on the persistence of populations within marine protected areas (MPAs). The effectiveness of MPAs at maintaining the species evolutionary potential will depend on the occurrence of self-sustaining and viable populations, harboring sufficient levels of genetic diversity. Here, individuals of Patella ferruginea Gmelin, 1791, an endangered and rare limpet endemic to the western Mediterranean, were genotyped using eight microsatellite loci. Genetic information was used to assess the occurrence of (1) self-sustaining and viable populations and (2) fine-scale spatial genetic structure within two MPAs in the north of Sardinia Island. In contrast to the literature-based expectation of two relict and declining populations, levels of genetic diversity were similar to those reported for other marine gastropods. Furthermore, the contemporary effective population size was higher than the average effective size found in populations of other endangered species. Even accounting for uncertainty, such estimates exceeded the critical threshold below which inbreeding and random genetic drift determine the loss of genetic diversity. The two populations showed different spatial genetic patterns, which might reflect the interplay between species life-history traits and topographic and oceanographic features. With regard to the conservation and management of marine resources, these results stress once more the importance of taking into account both the species life-history traits and the habitat features that can limit connectivity at small geographic scales.