Genetic population structure of four hydrothermal vent shrimp species (Alvinocarididae) in the Okinawa Trough, Northwest Pacific

Understanding the formative factors of connectivity among deep-sea chemosynthetic communities may clarify the biogeographic mechanisms that facilitate the establishment and development of vent/seep fauna. This study identified interspecific differences in the geographical distribution and genetic population structure of 4 alvinocaridid shrimp species inhabiting hydrothermal vents in the Okinawa Trough, Northwest Pacific. Shinkaicaris leurokolos populations were widely distributed at 580 to 1651 m depth, with partial nucleotide sequences of the mitochondrial COI gene revealing extremely high genetic diversity (haplotype diversity: 0.98 to 1.00). In contrast, local populations of Alvinocaris dissimilis and A. longirostris, both of which have narrower bathymetric distributions, were characterised by low haplotype diversity (0.29 to 0.52). In the Okinawa Trough, Alvinocaris sp. only occurs at the Irabu Knoll, but this species also inhabits the Suiyo Seamount on the volcanic front of the Izu-Bonin Arc (Northwest Pacific). This undescribed species had relatively high haplotype diversity (0.70 to 0.82), with no genetic differentiation between the 2 sites. Certain factors may allow this species to occur at both sites (e.g. a chemical environment derived from similar substratum), despite geological differences in hydrothermal circulation (i.e. a back-arc basin versus an arc volcanic front, respectively). The findings of this study indicate that (1) the wide geographical and bathymetrical distributional ranges of the vent shrimp species cause high genetic diversity associated with stable population connectivity and (2) certain environmental features (e.g. depth and substratum) and life-history traits (e.g. feeding habitat and larval characteristics) represent important formative factors in the connectivity of alvinocaridids in the Northwest Pacific.