Corals and Reef-Dwelling Fish Regulate Carbon Storage and Cycling Processes in Coral Reef Ecosystems

Coral reef ecosystems are among the most biodiverse and ecologically significant marine habitats; however, the carbon storage potential of these ecosystems and how corals and reef-dwelling fish participate in carbon cycling remain largely unexplored. In this study, stereo-video surveys, elemental analysis, and statistical modeling were used to quantify the carbon reservoirs of coral reef ecosystems in the South China Sea (SCS) in terms of carbon reservoirs in reef fish, coral communities, and sediment, and assess the factors influencing carbon storage. The results revealed that the average carbon stock of the SCS coral reef ecosystems is 3.22 kgC m^-2, with an estimated carbon storage of 25.73-121.99 TgC. Sediments are the dominant carbon reservoir and store 90.6%-95.7% of the total estimated carbon stock; however, coral and fish biomass also contribute to carbon stocks. The impact of corals and reef-dwelling fish on the carbon cycle of coral reefs far exceeds their direct carbon storage function, and reef fish communities transport an average of 235.63 gC m^-2 yr^-1 into the sediment carbon reservoir. These findings, reported for the first time, demonstrate the significant carbon sequestration potential of coral reef ecosystems, in which SCS reefs were used as an example, and provide critical insights into the role of corals and reef-dwelling fish in coral reef carbon cycling. These findings further highlight the necessity of biodiversity conservation amid increasingly severe global changes, specifically to maintain the carbon sequestration function and stability of coral reef ecosystems.