Genetic structure of the seagrass Posidonia oceanica in the western Mediterranean: Ecological implications

The seagrass Posidonia oceanica (L.) Delile plays a dominant role in coastal ecosystem dynamics in the Mediterranean Sea. This species reproduces both sexually through germination and asexually through vegetative propagation of subterranean rhizomes. Though flowering and fruiting are common, seedlings rarely succeed. An extensive population of P. oceanica on the coast of the Island of Ischia (Gulf oi Naples, Italy) was found to be nearly clonal when analysed with 2 DNA fingerprinting techniques, minisatellites and random amplified polymorphic DNA (RAPD); the results show similarity values of 1 and >0.91, respectively. Furthermore, a comparably high genetic similarity was observed between this population and individuals from another Ischia population and from the coast of Spain. These findings support clonal propagation as the dominant reproductive mode for this species. The presence of Limited numbers of genotypes in the Western Mediterranean basin coupled with a very slow rhizome elongation rate and the significant anthropogenic stress on these populations is cause for concern over the long-term ecological stability of this keystone species.