Strong genetic differentiation of the gilthead sea bream Sparus aurata (L., 1758) between the two western banks of the Mediterranean

We characterised four samples of gilthead sea bream from the two western Mediterranean banks with three microsatellite loci and two RAPDs systems. Contrarily to what could be predicted for a highly mobile species with a planktonic larval dispersal phase, we observed a strong and significant genetic differentiation at all loci between the two banks (F(st)=0.069(***)), whereas two samples from the Gulf of Lions were almost identical (F(st)=0.003 ns) while the two from the Gulf of Annaba displayed varied levels of differentiation according to the molecular marker considered. RAPDs showed a similar trend as microsatellites. The reasons for this surprisingly strong genetic differentiation, as compared to what has been observed in other species over comparable geographical distance, may be sought for either in a smaller as suspected larval dispersal, or in the non-neutrality of the loci studied.