High species richness of Northwest Pacific deep-sea amphipods revealed through DNA barcoding

Although deep sea has become a subject of intense studies in the recent years, our knowledge of the diversity of benthic organisms, especially at the molecular level, is far from complete. In the present study we focused on Amphipoda, known to be an abundant and diverse component of the marine zoobenthos. COI barcoding of an extensive collection of abyssal and hadal amphipods from the Kuril-Kamchatka Trench (KKT) area revealed 133 Molecular Operational Taxonomical Units (MOTUs). The richness of species varied between stations, with the highest observed in the areas where high organic carbon (C-org) content was recorded. Among the recognized MOTUs as many as 42% were singletons and only 28 were found at three or more stations. Their distribution was variable with seven taxa occurring at the most distant stations situated across the KKT. This shows that the trench does not constitute a barrier for the distribution of certain species. However, it may limit the gene flow in the case of others. The most common MOTUs were divided into three bathymetric categories: typically abyssal and hadal species as well as eurybathic ones inhabiting both the abyssal and hadal depth zones.