Importance and Threats to Corals

A report discussed in Nature in October 2025 announced that warm-water coral reefs have become the first major Earth system to pass a climate tipping point, beyond which it will be extremely difficult to reverse their decline without drastic action to halt and reverse climate change. The 2023-2025 global bleaching event has affected approximately 84% of reefs worldwide.

Climate change and ocean warming cause heat stress, leading to mass coral bleaching. In these events, the symbiotic algae, or zooxanthellae, that corals host can produce harmful free radicals above a certain temperature. This becomes toxic to the corals, causing them to expel the algae and turn white. Corals can sometimes readopt their symbionts at a later point and may survive for a short period without them, but prolonged marine heatwaves can lead to large-scale coral death. In shallow reef areas, excessive sunlight and UV exposure can further intensify this heat stress, especially when water temperatures remain high for extended periods.

In Southeast Asia, coral populations face numerous overlapping stresses. In the Coral Triangle and surrounding seas, including the Riau Archipelago, one of the biggest challenges is the intensification of coastal populations, shipping, tourism infrastructure, land reclamation, and industrial development. Around Singapore, reefs have long been affected by dredging, reclamation, port activity, and heavy shipping traffic, all of which increase sedimentation and turbidity. This leads to murky, sediment-rich waters that can cause light starvation. Ships and coastal works can also stir up sediment, creating “brown-out” conditions that block sunlight and restrict the corals’ ability to photosynthesise. Corals may also experience sonic stress from the noise of shipping, construction, and industrial activity.

These pressures are also visible in Bintan. In the north of the island, resort development in the Lagoi area has transformed parts of the coastline for tourism, while coastal construction, boating, and beach infrastructure can place pressure on nearby reef environments. In other parts of Bintan and the wider Riau Archipelago, land-use change, bauxite mining, plantation runoff, and aquaculture, including prawn ponds, can increase sediment, nutrients, and pollutants entering coastal waters. Coral reefs are highly sensitive to toxins and changes in water quality. Fertilisers, sewage, waste from plantations, and runoff from aquaculture can alter nutrient levels, fuel algal growth, and reduce coral health. Marine debris, including mostly plastics, degrade into microplastics over time, and can also introduce harmful substances, damage coral tissue, and block sunlight. Oil sludge and oil spills add further pressure, especially in busy maritime areas such as Singapore and the Singapore Strait.

Ocean acidification is another long-term stress. As more CO2 is absorbed by the ocean, seawater pH decreases and carbonate ions become less available, making it harder for corals to build their calcium carbonate skeletons. While acidification is not always the most immediate local threat compared with warming, sedimentation, and pollution, it can weaken reef growth and reduce long-term resilience.

A further local and regional issue is destructive fishing. Blast fishing uses dynamite to create underwater explosions that stun or kill fish, which then float to the surface and can be collected. This practice is banned in many ASEAN countries, but past and continuing blasts have damaged reefs and the breeding habitats of reef fish and corals. Other destructive practices, including cyanide fishing, trawling, careless anchoring, and trampling by visitors, can physically break coral colonies and slow reef recovery. Overfishing also removes herbivorous fish that normally graze algae; without them, algae can overgrow corals and prevent young corals from settling.

The video clips below share the perspectives and opinions of various collaborators on the importance of corals and the threats to these spaces.