Genetic Diversity of Populations of the Red Mullet Mullus barbatus Linnaeus, 1758 (Mulliformes: Mullidae) along the Bulgarian Black Sea Coast as Evident by Microsatellite Analysis

The red mullet Mullus barbatus holds significant ecological and economic value within the Black Sea fisheries. However, similar to numerous other species, the stocks of red mullet are currently being harvested at levels that are not sustainable. The knowledge of the genetic diversity is an essential prerequisite for maintenance of the resources of this species as well as for understanding its adaptation to various environmental pressures. In this case study, nine microsatellite markers were used to evaluate the genetic population structure of M. barbatus along the Bulgarian Black Sea coast. This investigation represents the initial assessment of such genetic patterns in this particular geographic area. Totally, 80 specimens were genotyped from two locations along the Bulgarian Black Sea coast, revealing 122 alleles. For the samples from both locations, the mean values of observed and expected heterozygosity were rather high (Ho = 0.628 and He = 0.696 for Balgarevo; Ho = 0.672 and He = 0.716 for Sveti Vlas), indicating a high level of genetic diversity. Our results showed a substantial level of migration occurring among populations of the studied species. The low Fst value (0.007) is primarily related to within-population variation (90.81%) and implies a low level of population differentiation. The Garza-Wiliamson index values, when combined with population size, show a decrease in genetic variation in the population studied because of a combination of high fishing pressure, habitat fragmentation and intrinsic fluctuations of the population size.