A recent study in the northern South China Sea offers a roadmap that could buy precious time for collapsing coral reefs across the tropics.
Summary:
- Local human pressures – especially overfishing, nutrient runoff, and coastal urbanisation – are shown to be a bigger immediate threat to northern South China Sea reefs than global warming alone.
- Fishing pressure is the strongest driver of coral decline, with reef fish decline closely linked to lower live coral cover across Hainan, Sanya, and Xisha.
- The study argues for tailored solutions by place: runoff and fisheries reform in Hainan, wastewater and sediment control in Sanya, and fish recovery plus starfish control in Xisha.
- Integrated land-sea management works well, with combined interventions producing much stronger reef recovery than isolated fixes.
- The message is urgent but hopeful: reefs are badly stressed, yet local policy action could buy time while climate change efforts catch up.
Bleached and dying coral has become a symbol of climate change, as characteristic as a polar bear stranded on an ice floe.
A new study from the northern South China Sea, near China's Hainan Island, however, delivers a surprising and more hopeful message. Importantly, local human activities, such as overfishing, agricultural nutrient runoff, and rapid coastal urbanisation, are doing more damage than rising sea temperatures.
That matters far beyond China. From the Coral Triangle (spanning Indonesia, Malaysia, the Philippines, Papua New Guinea, Timor-Leste, and the Solomon Islands) to the Caribbean, the findings point to a practical conservation strategy: global climate change is difficult to control in any single region, but in the near term, localised pressures can be managed through targeted policies. That is the core argument made by a lead author of the study, Assistant Professor Tong Liu at the Lee Kuan Yew School of Public Policy.
Why coral reefs matter
Coral reefs are often called the rainforests of the sea. They cover less than one per cent of the ocean floor but support roughly 25 per cent of all marine species. In the Coral Triangle alone, over 120 million people directly depend on reef ecosystems for food and income.
“The most affected groups are often small-scale fishermen who have relied solely on fishing for generations, low-income families, and groups with limited livelihood options,” said Asst Prof Liu. These groups typically lack the funds and capacity to transition to deep-sea fishing, tourism, or aquaculture, requiring greater education and financial guidance.
Moving from environmental degradation to human crisis is rarely a single dramatic event. As Asst Prof Liu highlighted: "The loss of resilience is a gradual process. The crisis has already started once local residents face malnutrition or begin migration."
Damage beneath the surface
Globally, the picture is grim. Since the 1950s, the world has lost approximately 50 per cent of its live coral cover (LCC), which is the percentage of a reef’s surface covered by living corals – a key indicator of overall reef health.
Marine heatwaves are becoming more frequent and intense, triggering mass bleaching events from Australia's Great Barrier Reef to the Maldives to the Caribbean. Bleaching occurs when heat-stressed corals expel the colourful algae that live inside their tissues, turning them white and often leading to death.
The northern South China sea is no exception. Over two decades of field monitoring, the researchers documented a 40 per cent decline in LCC. Current levels now average around 19 per cent, far below the global average of 30 per cent.
The damage, however, was uneven throughout Hainan, Sanya, and Xisha. Crucially, the study finds that local pressures compound one another. Fishing pressure emerged as the dominant driver across all three subregions: a 10 per cent decrease in reef fish density corresponded to a 3.5 to 7.3 per cent reduction in LCC, depending on location. But the mechanisms differ by context.
On Hainan's east coast, overfishing combines with agricultural nutrient pollution to create a devastating twin pressure. Depleted fish populations can no longer control algae, while excess nitrogen from fertiliser runoff fuels macroalgae blooms that outcompete young coral. The result is a permanent coral-algae phase shift that makes recovery difficult.
Around Sanya in the south, rapid urbanisation is the culprit. The population surged as rural migrants flocked to the coast, and tourism arrivals soared in the 2000s. Wastewater treatment infrastructure could not keep pace. Sediment from coastal construction smothered reefs, and nutrient-rich sewage fed algal growth.
In the remote Xisha Islands, the story is different, but the root cause is similar. Overfishing removed predator species that naturally control crowns-of-thorns starfish (CoTS). When an outbreak occurred between 2005 and 2009, there was nothing to stop it. The starfish consumed coral faster than it could recover.
Climate warming also plays a role. While healthy corals in pristine conditions can better withstand and recover from thermal stress, reefs degraded by overfishing and pollution are less resilient when heatwaves hit. But the data clearly shows that local stressors explain 73 per cent of the variance in LCC; thermal stress explains less.
The fix starts close to shore
This is where the study moves from diagnosis to prescription, offering cautious optimism. The researchers modelled four intervention scenarios, supported by recent conservation practices. The results are striking.
In Hainan's east coast, reducing agricultural nutrient runoff by 60 per cent (back to 1990s levels) and doubling reef fish density through fisheries management lifted LCC by two to four times under continued warming. Importantly, the minimum coral cover crossed the 10 per cent threshold required for reefs to maintain their calcium carbonate structure. Below that, reefs physically collapse.
In Sanya, where urbanisation drives degradation, the modelling shows that upgrading wastewater treatment and controlling sediment from construction sites yields meaningful improvements, though recovery is slower due to the intensity of coastal development.
In the Xisha Islands, where land-based pollution is minimal, the priority is different. Simply restoring fish populations to around 250 individuals per 100 square metres – achievable through no-take zones and seasonal fishing bans – was enough to push coral cover above the collapse threshold. CoTS removal adds further protection.
Overall, integrated land-sea management outperforms isolated interventions. Smarter fisheries management and nutrient reduction are two helpful practices – together, the synergy lifts coral cover far more.
Is there a roadmap?
The study proposes an Integrated Coast-Reef Management (ICRM) framework with five steps: quantitative evaluation, stressor identification, tailored strategies, implementation and enforcement, and regulation and maintenance.
On paper, this sounds sensible. In practice, not so easy. The framework requires coordination across agriculture, fisheries, urban planning, tourism, and environmental agencies – often at multiple levels of government.
The authors acknowledge the challenge but point to existing mechanisms. In China, the summer fishing ban (strictly enforced since 2015) and marine protected areas provide institutional scaffolding. The question is whether these can be adapted for integrated, cross-sectoral management. “The real value lies in observing which practices are effective,” Asst Prof Liu noted, referring to cases such as Apo Island and the Karimata region.
The study suggests starting with a simple diagnostic: measure live coral cover, fish biomass, nutrient levels, and CoTS abundance. Then identify the dominant local stressor. In some places, it will be fishing. In others, pollution. In remote atolls, it may be starfish outbreaks. Tailor the intervention to the diagnosis.
Funding remains the hardest question. The authors note that agricultural green development, precision fertilisation, wetland buffers, and nutrient recycling, can be cost-negative over time, reducing fertiliser bills while saving reefs. Fisheries restoration through no-take zones and fish seed release requires upfront investment but pays dividends in catch outside protected areas.
"The conversation needs to shift from conservation as a cost to conservation as an investment," said Asst Prof Liu. "Reefs provide storm protection, tourism revenue, and fisheries. Protecting them saves money in the long run."
The authors recommend a tripartite governance model comprising a multi-stakeholder "science-policy hub" to translate data into action; tiered responsibility where local authorities handle day-to-day interventions and national budgets fund infrastructure; and "blue finance" instruments to supplement traditional funding through ecosystem service payments and public-private partnerships. Enforcement, they argue, should shift from "police-style" to "community-led management", with local stakeholders involved in monitoring and compliance.
Coral reefs are not waiting for a perfect plan. They are bleaching, breaking down, and disappearing while policy debates stall and funding cycles churn. But the science is clear, the tools exist, and the cost of inaction outweighs the cost of intervention. What reefs need now is political will translated into enforceable action – not whether we can save them, but whether we choose to before the window shuts for good.
Read more in this policy brief by Assistant Professor Tong Liu.