Coral reefs: Warming ocean waters fuel fourth global bleaching event

The health of the world's coral has significantly deteriorated, scientists at the world's top coral reef monitoring body warned Monday (Apr. 15).

Experts from the National Oceanic and Atmospheric Administration (NOAA) and International Coral Reef Initiative (ICRI) said that coral reef bleaching across at least 53 countries, territories or local economies has been confirmed from February 2023 to now.

"Today's announcement is basically a warning that, you know, we're seeing climate change impacts, simultaneously impacting essentially coral reefs around the entire planet,"  Derek Manzello, NOAA Coral Reef Watch coordinator said.

"Mass coral bleaching events due to ocean temperatures started, the first time it was documented was 1982, 1983." Coral reefs are important ecosystems that sustain underwater life, protect biodiversity and slow erosion. They also support local economies through tourism.

This year's bleaching follows the declaration that 2023 was the hottest year on record.

Bleaching happens when stressed coral expel the algae that are their food source and give them their colour. This can result in coral death.

Warming oceans are no good news for coral reefs. 

"Currently, more than 54% of the reef areas around the globe have experienced, bleaching level heat stress in the last year. And that number is growing by about 1% per week. The previous record was 56% of the reef areas experienced bleaching level heat stress during the third global coral bleaching event, which took place from 2014 to 2017. So this event is likely to become more spatially extensive than that event within the next couple of weeks," Manzello said.

Coral death can be avoided if the stress driving the bleaching diminishes. Coral can then recover with reefs maintaining their biodiversity and continuing to provide the ecosystem services that we rely on.

The International Coral Reef Initiative, a partnership of 101 international members, has developed strategies to increase the emphasis on their restoration and has incorporated resilience-based management practices into its 2018 strategic plan.

But action must be taken now. 

"This problem won't go away until there is international cooperation to reduce greenhouse gas emissions,"  Derek Manzello says.

"This problem's only going to get worse as time goes on and the oceans continue to warm, unfortunately. In the interim, one of the goals of, you know, the management science community is to try to reduce all the additional stressors that might be impacting reefs."