Coral reefs rapidly die from marine heatwaves

Coral reefs rapidly die from marine heatwaves

During the extreme temperature event the team studied, which occurred on the Nice Barrier Reef between 2016 and 2017, there was an estimated lack of a 3rd to half of the corals.

In 2016 the team's research showed that just a 0.5C increase in ocean temperature changes the extent of mortality that happens in coral during bleaching.

But the new study found that severe marine heatwaves can actually degrade the skeletal structure of the coral, potentially killing the organisms in a matter of days or weeks.

The scientists concluded that severe and frequent marine heatwaves can destroy corals through a processes called "bleaching".

"The severity of these heatwave events is beyond the bleaching process, it's actually a point where the coral animal itself is dying", said Dr Tracy Ainsworth, a co-author of the study from the University of New South Wales.

As per new research carried on by the University of New South Wales (UNSW), the University of Technology Sydney, the University of Newcastle, the US NOAA, and James Cook University, ocean heatwaves due to global warming affect coral reefs worldwide more than scientists expected. They suggest that severe heatwave-induced mortality events should therefore be considered a distinct biological phenomenon, with more direct damage different from coral bleaching. "The water temperatures are so warm that the coral animal doesn't bleach-in terms of a loss of its symbiosis-the animal dies and its underlying skeleton is all that remains".

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Ocean heatwaves are also leading to the multiplication of bacteria and algae that are harmful to coral reefs all over the world.

The researchers used CT scans of coral reefs to monitor the impact of extreme temperatures. "We show that this process is devastating not just for the animal tissue, but also for the skeleton that is left behind, which is rapidly eroded and weakened". "But what we're seeing here is that - when the coral tissue dies - it falls and breaks away from the skeleton", Dr Ainsworth explained.

"It confirms that we are on a trajectory where heatwave events and heat stress is becoming so severe it's beyond the capacity of the ecosystem to withstand it", she told AAP.

Commenting on the research, Dr James Guest from Newcastle University in the United Kingdom, who has been studying coral reef habitats for more than 15 years, said: "It's hard to know just how much we have to keep saying that this is a big problem before policy-makers decide to do something about it". This discovery fits into this category.

The effects of climate change on coral reefs is fairly well-known; most schoolchildren have seen side-to-side comparisons of lively, healthy coral reefs juxtaposed with bleached, lifeless ones, caused by pollution and other human activities.

"Across the globe coral reefs are still a source of inspiration and awe of the natural world, as well as being critically important to the communities that rely upon them".

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