Tropical seagrass meadows and coral reefs often function as interconnected marine habitats, but they are often studied and managed as homogenous units. As macrohabitats, seagrass meadows provide important benefits to adjacent reef ecosystems by acting as natural filters of sediments and nutrients, and by providing critical feeding, nursery, and refuge habitats for reef fishes and other fauna. Whilst the macrohabitat functions of seagrass meadows have been often acknowledged, their microhabitats functions have largely been neglected. The purpose of the study is to explore how seagrass meadows provide multiple benefits to adjacent coral reefs through various microhabitat functions. The paper reveals some of the diversity of microhabitats that seagrass meadows contain, such as macroalgal mats, rubble cavities, sand patches with sparse seagrass, anemone gardens, hard substratum, and sponges mixed with seagrass. We highlight the ways in which reef creatures have diversified and specialized in using these different microhabitats, and postulate that seagrass microhabitat diversity enhances the habitat function and faunal diversity of seagrass meadows.

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.

Global change has generated challenges for oceans, from individuals to the entire ecosystem, and has raised contemporary issues related to ocean conservation and management. Specifically, coral reef ecosystems have been exposed to various environmental and human disturbances. In this study, the Ecopath with Ecosim model was used to explore the impacts of ocean warming and fishing on Xisha Islands coral reef ecosystem in the South China Sea. The variables in this model included two ocean warming scenarios and three fishing scenarios. The model consisted of 23 functional groups including algae, coral, sea birds, and sharks. Our results showed that by the middle of the century, ocean warming and fishing led to a 3.79% and 4.74% decrease in total catch compared with 2009, respectively. In addition, the combined effects of ocean warming and fishing caused a 4.79% decrease in total catch, and the mean trophic level of catch was predicted to decrease by 6.01% under the SSP585-High fishing scenario. Reducing the fishing effort mitigates the effects of ocean warming on some species, such as large carnivorous fish and medium carnivorous fish; however, under low fishing effort, some functional groups, such as small carnivorous and omnivorous fish, have low biomass because of higher predation mortality.