Malaysia's coral under threat? What you need to know about bleaching

SHAH ALAM - Malaysia’s vibrant coral reefs, known for their rich marine diversity, are now under severe threat from coral bleaching.

Reef Check Malaysia’s marine biologist and programme coordinator Alvin Chelliah said that coral bleaching happens when corals expel the algae that live within their tissues, resulting in a pale or white appearance.

He added these algae, known as zooxanthellae, were crucial for providing nutrients through photosynthesis and for giving corals their vivid colours.

“Several factors can trigger coral bleaching, but the primary cause is prolonged exposure to high sea temperatures.

“When water temperatures rise, corals become stressed and they expel the algae as a survival mechanism. Without the algae, corals lose their major food source and are more vulnerable to disease and mortality,” he said when contacted recently.

Chelliah also highlighted that climate change exacerbated coral bleaching by increasing ocean temperatures and causing more frequent and intense heat waves.

The ongoing stress reduced corals' chances to recover between bleaching events.

Additionally, factors such as pollution, runoff and marine debris could further stress corals on a more localised scale.

Chelliah said that the impact of coral bleaching extends beyond the corals themselves.

He said if bleaching leads to widespread coral death, it could cause an ecosystem collapse, disrupting the food web, reducing biodiversity and weakening coral reproduction and growth.

In the long term, this results in death and loss of critical marine habitats.

Life cycle of corals

Chelliah said the life cycle of corals involves several crucial stages essential for the growth and maintenance of coral reefs.

He said it started with spawning and reproduction, where corals reproduce sexually during synchronised spawning events, influenced by environmental cues like water temperature and lunar cycles.

During this process, he added corals release gametes (eggs and sperm) into the water, leading to external fertilisation and the formation of microscopic larvae called planulae.

“These planula larvae are free-swimming and drift in ocean currents for days to weeks before settling on a suitable substrate.

“Once they find a suitable surface, such as existing coral skeletons or rocky surfaces, they undergo settlement and polyp formation, attaching and transforming into juvenile polyps.

“These polyps secrete calcium carbonate to build their skeletons and grow into colonies through a process called budding. As these colonies expand, they contribute to colony growth and reef formation, creating the extensive coral reefs we see today,” he said.

Chelliah added the reefs were further maintained through the continuous deposition of calcium carbonate, which strengthened the reef structure.

However, he emphasised that vulnerability to coral bleaching could occur at various stages of this life cycle. However, it is particularly detrimental during critical periods like spawning or larval settlement.

He also highlighted that bleaching during these stages can significantly reduce coral survivorship and hinder the replenishment of coral populations.