Ophiuroid fauna of cobalt-rich crust seamounts in the Northwest Pacific Ocean

Seamounts are vulnerable ecosystems in the deep sea and can be heavily impacted by human activities,such as bottom fishing and deep-sea mining.The species composition and distribution patterns of benthic fauna is key information for the designation of marine protected areas and environmental management plans.Three contracts for cobalt-rich crust exploration have been granted to China,Japan and Korea in the Northwest Pacific Ocean by the International Seabed Authority.However,our knowledge of benthic biodiversity in this area is extremely insufficient.During 2013–2020,eight Chinese Ocean Mineral Resources R&D Association(COMRA)cruises were conducted to investigate the benthic assemblages of nine seamounts in this region.In this study,191 ophiuroids collected from seamounts in the Northwest Pacific were identified into 29 species in 11 families.Ophiacanthidae and Euryalidae were the two most dominant families with 12 and 6 species,respectively.Ophiotomidae and Ophiopyrgidae were represented by two species each,while seven families were represented by only one species.Four species were widely distributed among 4–5 seamounts,and 17 species were found only at a single site.An integrated regional taxonomic dataset of Ophiuroidea was generated and analyzed.A total of 23 and 14 species were obtained from the Magellan Seamount Chain(MSC)and the Marcus-Wake seamounts(MWS),respectively,with 8 species shared between the two seamount groups.The individual-based rarefaction curves did not reach an asymptote,suggesting that the sampling effort was inadequate for either the entire region or each single seamount.Most species distributed in a narrow depth range,and the species composition was different between water depths above and below 2000 m.Our results greatly improve the understanding of megafaunal biodiversity from seamounts in the Northwest Pacific Ocean,and highlight the necessity of further surveys to provide more robust information for environmental protection and management in this region.

Morphological description and population structure of an ophiuroid species from cobalt-rich crust seamounts in the Northwest Pacific:Implications for marine protection under deep-sea mining

Many seamounts are covered with cobalt-rich ferromanganese crusts,and are increasingly attracting interest for the potential extraction of valuable mineral resources from deep seabed environments.However,the impacts of potential mining activities on the vulnerable seamount ecosystem remain unclear.To enhance the understanding of connectivity in benthic invertebrate populations in the Northwest Pacific,several seamounts were surveyed and biological samples collected.In the present study,the ophiuroid species Ophioplinthaca defensor is reported for the first time from four deep seamounts in the Northwest Pacific,and described,providing more detailed morphological diagnosis characters.To assess the population structure of the species between and within seamounts,two mitochondrial markers(COI and 16 S)were sequenced.In total,20 haplotypes from 32 COI sequences and 8 haplotypes from 3716 S sequences were recovered.The star-shaped TCS networks and nonsignificant pairwise population differences reveal the absence of distinct population structures between and within seamounts.In addition,the O.defensor population seemed to have undergone a demographic expansion in history.This is the first study on the genetic population structure of a benthic invertebrate from seamounts in the Northwest Pacific,and this results suggest a potentially high,long distance dispersal capacity in O.defensor between seamounts,which could inform the development of the Regional Environmental Management Plans for the cobalt-rich crust seamounts in the area.