Bathymetric and Molecular Diversity in two Marine Crab Species

Liocarcinus depurator and Geryon longipes are two crab species which widely differ with regard to the marine depths they inhabit and their associated environmental characteristics. The bathymetric distributions and molecular diversity were studied along the Atlantic-Mediterranean transition for the two species. A fragment of the COI (Cytochrome Oxidase subunit I) mitochondrial gene was studied in both species. In the case of L. depurator, a large number of haplotypes were detected and could be classified in two large haplogroups. One was predominant in water masses of Atlantic origin, and the other in Mediterranean waters. Three main areas were observed concerning the relative distribution of these two haplogroups: Gulf of Cadiz, Alboran Sea, and Levantine/Catalan coasts. Only eight haplotypes were detected in G. longipes. In this species and according to its haplotype distribution, three regions could be described: Alboran Sea, Gulf of Vera (between Cape Gata and Cape Palos), and Levantine/Catalan coasts (the species is apparently absent from the Gulf of Cadiz). In L. depurator, the marine currents and oceanographic fronts affecting larval dispersion could explain the pattern of haplotype distribution. A similar, but not exact pattern is shown by G. longipes, despite its markedly different habitat and depth they inhabit. The similarities in genetic structure may be accounted for by the epipelagic habitat of the larvae, which are the life history phase where most of the geographic dispersion takes place