South China Sea coral reefs are storing carbon at levels once thought exclusive to mangrove forests and seagrass beds—a discovery that reframes how scientists understand the climate value of Earth's most vibrant underwater ecosystems. A research team led by Prof. Qian Peiyuan at The Hong Kong University of Science and Technology, alongside researchers from the Institute of Zoology at the Chinese Academy of Sciences and the Southern Marine Science and Engineering Guangdong Laboratory, has quantified just how much carbon these reefs sequester, revealing findings that challenge decades of overlooked potential.
Coral reefs have long been celebrated for their biodiversity and productivity, yet their role as carbon reservoirs remained poorly understood—a critical gap for climate science. The team developed a novel method combining stereo-video surveys, elemental analysis, and statistical modeling to measure carbon stored across three critical reef components: fish biomass, coral communities, and surface sediments. The results showed that South China Sea coral reefs store carbon nearly equivalent to, if not exceeding, the country's blue carbon ecosystems—mangroves, salt marshes, and seagrass beds—which have been recognized as essential for global climate mitigation.
The breakthrough reveals sediment as the dominant carbon pool on coral reefs, while coral and fish biomass also meaningfully contribute to overall carbon stock. This matters enormously: when coral reef ecosystems degrade, they lose capacity to store carbon and risk releasing previously sequestered carbon into the ocean and atmosphere. The team analyzed contributions from reef-dwelling organisms through pathways of calcification, production, bioerosion, excretion, and respiration. By synthesizing results from over fifty studies of coral reef hotspots globally, they identified a positive trend in both net calcification and net production at the ecosystem level, indicating that coral reefs operate as dynamic, complex systems continuously exchanging and redistributing carbon.
Perhaps most strikingly, reef fish exert disproportionate influence on coral reef carbon budgets. Fish are estimated to transport relatively large amounts of carbon into sediment reservoirs annually—a contribution far exceeding what their direct biomass alone would suggest. This finding underscores an ecological truth: conserving reef animal populations isn't simply about maintaining biodiversity or species beauty. It's about preserving the mechanisms that allow sediments to function as long-term carbon vaults.
Prof. Qian captured the broader significance: "Our study demonstrates the significant carbon sequestration potential of coral reef ecosystems, using SCS reefs as an example, and provides critical insights into the role of corals and reef-dwelling fish in coral reef carbon cycling. These findings highlight the necessity of biodiversity conservation amid increasingly severe global changes, specifically to maintain the carbon sequestration function and stability of coral reef ecosystems."
As climate solutions increasingly focus on natural carbon sequestration, this research repositions coral reefs from being viewed primarily through the lens of conservation and tourism to being recognized as active participants in planetary carbon cycles. The work, published in Advanced Science by Yiting Chen and colleagues, suggests that protecting reef ecosystems isn't just an environmental imperative—it's a climate strategy.