Thai researchers help corals cope with global warming risk

Coral bleaching occurs when corals lose their vibrant colours and turn white due to changes in the ocean environment, particularly rising sea temperatures, tourism, fishing activities, and pollution.

A 2024 report by the International Union for Conservation of Nature (IUCN) revealed that 44% of reef-building coral species worldwide are at risk of extinction. 

Meanwhile, a 2018 report by the Intergovernmental Panel on Climate Change (IPCC) warned that if the average global temperature rises by 1.5°C, coral reefs could decline by 70–90%. If the temperature increase reaches 2°C, up to 99% of coral reefs could be lost.

In response to this critical issue, Suchana Chavanich, deputy director of Chulalongkorn University’s Aquatic Resources Research Institute, has been conducting research on coral propagation since 2005 at the Sichang Marine Science Research and Training Station in Chonburi province.

The research found that corals are better able to adapt and survive under global warming conditions when raised in high-temperature environments from birth.

Naturally, corals reproduce in two ways:

• Sexual reproduction, where corals release eggs and sperm into the water during a full moon night. However, only about 0.001% of these fertilised eggs survive to become mature corals, due to predation and unsuccessful fertilisation.
• Asexual reproduction, where fragments of coral break off and, if they fall into a suitable environment, can grow into new coral colonies. This method has a survival rate of around 50%, though it results in lower genetic diversity.

Both natural reproduction methods are slow processes. In the context of global warming, sexual reproduction rates have dropped even further. “If we allow corals to regenerate naturally, they may not recover quickly enough to replace those lost to bleaching events, risking extinction in the near future,” Suchana explained.

To accelerate coral recovery, the Aquatic Resources Research Institute has collaborated with the Plant Genetic Conservation Project and the Royal Thai Navy’s Naval Special Warfare Command to propagate corals through artificial fertilisation techniques.

Under this method, researchers collect coral reproductive cells—both eggs and sperm—during the full moon nights. These are fertilised in wells to produce coral larvae, which are then encouraged to settle on specially prepared bricks. 

The juvenile corals are reared in nurseries for two years before being transplanted back into the sea, where they grow for an additional three years. By the age of five, the corals are mature enough to spawn for the first time.

“This method significantly improves the survival and growth rates of corals,” Suchana said.

Not only is artificial fertilisation being used, but researchers are also simulating global warming conditions to enhance the natural resilience of corals. 

The research team places coral larvae, produced through artificial fertilisation, in nurseries with a high temperature of 34°C, compared to the normal range of 30-32°C. After two years, the surviving larvae are then returned to the sea.

It was found that these corals adapted better to the warmer sea temperatures than naturally occurring corals, giving them a higher chance of surviving bleaching events.

However, the cost of conserving corals using artificial fertilisation and maintaining them in nurseries for two years can be relatively high. The cost is approximately US$100 (3,367.85 baht) per coral larvae, compared to just $1 (33.67 baht) for a coral frag.

Despite the cost, the research team believes it is a worthwhile investment, as it produces new coral strains that have learned to survive and thrive in higher sea temperatures due to global warming. 

Additionally, once these corals reach maturity, they will release reproductive cells into the sea simultaneously. When this phenomenon occurs, the research team dives to collect these cells for further artificial fertilisation, producing new climate-resilient corals.

Suchana emphasised that coral conservation cannot be achieved by scientists alone; it must be a multi-faceted approach. Efforts need to include coral reef restoration, reduction of pollution and greenhouse gas emissions, long-term financial support, and the involvement of all sectors—especially the government, private sector and the general public.

These efforts will be key to protecting and restoring coral reefs for the future. With the right actions in place, corals may be able to recover and continue to thrive as a vital marine ecosystem, she said.