Two-thirds of coral killed from severe heatwaves

A substantial loss of coral reef from heatwaves in Central Indian Ocean have been recorded by researchers.

Bleached and dead coral reef. © ZSL

A study carried out by the Zoological Society of London (ZSL) found that about 70 per cent of hard coral populations were decimated after extreme periods of high temperatures over two years.

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Reef health was monitored between 2015 and 2017, and for nearly two months at the start of the study seawater temperatures around the area were abnormally high.

Researchers compared surveys of the archipelago’s coral reefs before and after the heatwave in 2015 to monitor the damage. Their findings showed that 60 per cent of coral had died from the rise in temperature with some species more susceptible than others.

A year later, another heatwave struck the British Indian Ocean Territory, which lasted four months. The surviving corals from 2015 suffered yet again, with data collected suggesting 68 per cent of them were bleached and 29 per cent perished.

Bleached coral close up. © ZSL
Bleached coral close up. © ZSL

Even though these figures seem discouraging, the study found that of those surviving corals from 2015 comparatively fewer of them died the following year, despite the heatwave lasting a lot longer.

It’s thought the remaining coral are more resilient to increasing sea temperatures, and their ability to endure and regenerate may be significant in conserving reef populations from climate change-induced temperature increases.

Young coral regrowing. © ZSL
Young coral regrowing. © ZSL

Marine biologist and head of ZSL’s Institute of Zoology, Dr Catherine Head, says, “It is encouraging that reefs may have some degree of natural resilience, though further research is needed to understand the mechanisms by which some corals are able to protect themselves. This may be our best hope to save these vital habitats from the catastrophic effects of climate change.”

Hard corals, or Scleractinia, are animals closely related to sea anemones and form when individuals, known as polyps, group together and construct a hard calcium carbonate skeleton around their soft bodies.

These corals are the foundation of reefs, creating unique habitats that sustain a quarter of all marine species and provide people with food and protection from storms and high tides. These animals are in global decline, but the exact reasons why are still difficult to identify.

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Main image: Bleached and dead coral reef. © ZSL