Heatwaves kill coral reefs far faster than thought

In fact, though the study focused on the effects of ocean heatwaves during the heatwave that hit Australia's Great Barrier Reef in 2016, researchers determined that this heatwave phenomenon affected 37% of coral reefs globally between 2014 and 2017.

According to this new study, extreme spikes in ocean temperatures can cause entire coral reef systems to decay and collapse in a matter of days. These increasingly severe thermal conditions are causing an unprecedented increase in the frequency and severity of mortality events in marine ecosystems, including on coral reefs. The degradation also puts at risk many other sea creatures that live in the sea coral.

Also, the researchers revealed that not only coral bleaching is threatening corals, but warmer seawater temperatures are also endangering the marine organisms.

The report showed that a severe marine heatwave will not only trigger bleaching events, but can lead to heat-induced death of the coral itself. "Corals can survive a bleaching event, but they are under more stress and are subject to mortality", the US' National Oceanic and Atmospheric Administration (NOAA) explains on its website. "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".

The researchers used CT scans of coral reefs to monitor the impact of extreme temperatures.

"We are just going so far beyond what's normal". "But what we're seeing here is that - when the coral tissue dies - it falls and breaks away from the skeleton", Dr Ainsworth explained. "Adopting these techniques more broadly will be central to understanding how this process occurs on reefs globally - we anticipate that heatwave mortality events, and rapid reef decay, will become more frequent as the intensity of marine heatwaves increase". This discovery fits into this category.

The team has also shown that even the skeletons are being eroded by the rapid growth of algae and bacteria, another unexpected product of severe heatwaves. "As we begin now to understand this impact, the question is how many more of these "unknown unknowns" might there still be that could bring faster and greater damage to coral reefs from climate change", he said.

Commenting on the analysis, Dr James Guest from Newcastle University in the United Kingdom, who has been researching coral reef habitats for more than 15 years, said: "It is onerous to know how a lot we've got to keep saying that this is a huge problem before policy-makers resolve to do something about it".

"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", said Ainsworth.