Gene pool and connectivity patterns of Pinna nobilis in the Balearic Islands (Spain, Western Mediterranean Sea): Implications for its conservation through restocking

Pinna nobilis is an endemic bivalve of the Mediterranean Sea, and a vulnerable species registered as endangered and protected under the European Council Directive 92/43/EEC and Barcelona Convention. In early autumn 2016, a mass mortality event impacted P. nobilis populations in the south-western Mediterranean Sea, including the Balearic Islands. At the time of this study, P. nobilis still maintained high population densities along the Balearic coasts (Western Mediterranean). This study evaluated the connectivity of P. nobilis post-larvae and adults in seagrass habitats around the Balearic Islands and identified its source and sink populations. These objectives were reached through a multidisciplinary approach including population genetics (10 microsatellites) and hydrodynamic modelling. High genetic diversity was found and significant genetic differentiation (inferred by fixation index F) was detected between post-larvae samples, but not between adult populations. Significant genic and genotypic differentiation was recorded for adults and post-larvae. This pattern was confirmed by correspondence analysis using allele frequencies. The genetic connectivity pattern was consistent with marine currents and dispersal models. This work not only improves knowledge of the P. nobilis gene pool in south-west Mediterranean populations and their connectivity patterns, but is also crucial to help evaluate the possibility of recovery from source populations and the possibility of restocking programmes, as well as provide a solid base to establish effective marine reserve networks.