Checklist of the coral fish fauna of Xisha Islands, China

The Xisha Islands are composed of the Yongle Islands and the Xuande Islands in Hainan Province, China. It has one of the highest species diversity in the world and is also a typical oceanic distribution area of coral reefs globally. The ichthyofauna of the Xisha Islands were recorded by underwater visual census in May 2019 and July 2020. The survey data were combined with previous records of species into the checklist of the Xisha Islands presented herein. A total of 691 species, belonging to 24 orders and 97 families, was recorded. The major families were Labridae, Pomacentridae, Serranidae, Chaetodontidae, Hexanchidae, Lutjanidae, Scaridae, Gobiidae, Scorpaenidae and Carangidae. In this study, the Coral Fish iversity Index (CFDI) of six families (Chaetodontidae, Pomacanthidae, Pomacentridae, Labridae, Scaridae and Acanthuridae) was 229, indicating 756 coral fishes. In terms of the IUCN Red List, one species is Critically Endangered (Glyphis gangeticus), six species are Endangered (Stegostoma fasciatum, Aetomylaeus maculatus, Aetomylaeus vespertilio, Epinephelus akaara, Cheilinusundulatus sp. and Xiphias gladius), 16 species are Vulnerable, and 13 species are Near Threatened in the Xisha Archipelago, so conservation should be strengthened in this area in the future. One species is a new record for China (Dischistodus pseudochrysopoecilus) and 23 species are newly found in the Xisha Islands.

High-resolution acoustic data revealing peri-platform sedimentary characteristics in the Xisha Archipelago, South China Sea

Newly collected high-resolution acoustic data are used to describe the morphologies and sedimentary characteristics along the slopes of isolated carbonate platforms in the Xisha (Paracel) Archipelago. Base on multibeam bathymetric and seismic data, we identified seven types of morphological and depositional features around the platforms, including erosive grooves, mass transport deposits (MTDs), gullies, confined channels, canyons, mounded sediments and marginal contourite depressions. The occurrence of erosive channelized features around the platforms indicate that gravity flow is a major sediment-export mechanism for the transportation of excess neritic carbonates towards the slope. Marginal contourite depressions and mounded sediments are interpreted as bottom-current reworking products, suggesting an important role of bottom current and deep-water circulation of the South China Sea in shaping the slope morphology of the carbonate platforms. Furthermore, the bottom-current products tend to develop along the slopes of the carbonate platforms at the Xisha Uplift margin, in particular, erosional features formed by bottom current frequently occur in the southern side of the carbonate platforms. By comprehensive analysis of morphological and depositional features, we establish a facies model around the carbonate platforms to interpret different sedimentary transport processes, such as off-platform and along-slope sediment transport processes. These findings highlight a notable and complex relay-style channelized transport system consisting of grooves/gullies-channels-canyons, which has implications for linking neritic carbonate platforms into deep-sea basins.

Checklist of the coral fish fauna of Xisha Islands, China

The Xisha Islands are composed of the Yongle Islands and the Xuande Islands in Hainan province, China. It has one of the highest species diversities in the world and is also a typical oceanic distribution area of coral reefs globally. The ichthyofauna of the Xisha Islands were recorded by underwater visual census in May 2019 and July 2020. The survey data were combined with previous records of species into the checklist of the Xisha Islands presented herein. A total of 691 species belonging to 24 orders and 97 families was recorded. The major families were Labridae, Pomacentridae, Serranidae, Chaetodontidae, Hexanchidae, Lutjanidae, Scaridae, Gobiidae, Scorpaenidae, and Carangidae. In this study, the coral fish diversity index (CFDI) of six families (Chaetodontidae, Pomacanthidae, Pomacentridae, Labridae, Scaridae, and Acanthuridae) was 229, indicating 756 coral fishes. In terms of the IUCN Red List, one species is Critically Endangered (Glyphis gangeticus), six species are Endangered (Stegostoma fasciatum, Aetomylaeus maculatus, Aetomylaeus vespertilio, Epinephelus akaara, Cheilinusundulatus sp., and Xiphias gladius), 16 species are Vulnerable, and 13 species are Near Threatened in the Xisha Archipelago, so conservation should be strengthened in this area in the future. One species is a new record for China (Dischistodus pseudochrysopoecilus) and 23 species are newly found in the Xisha Islands.