12 October 2017
Maldives coral reef, 2016.  Photo: Paul Muir
Large areas of reef were heavily damaged during the mass coral bleaching event of 2016 associated with unusually warm sea temperatures. This was the most severe event on record and in the Maldives most of the corals were bleached white and will probably die over the ensuing weeks. This research suggests that divers may have to dive deeper in future if they want to see healthy coral. Photo: Paul Muir

A team of researchers led by a Global Change Institute adjunct from the Museum of Tropical Queensland (MTQ) has revealed that corals living in deeper reefs could be vital in the global effort to save shallow coral reefs.

MTQ’s Coral Collection Manager Dr Paul Muir said coral bleaching caused by unusually high sea temperatures was one of the greatest threats to coral reefs.

“When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white,” Dr Muir said.

“To date, limited understanding of the effects of coral bleaching in deeper waters and within individual coral species has impeded global management of its devastating impacts.”

During the 2016 bleaching event in the Maldives, Dr Muir and a team of experts from Australia, New Zealand and Maldives studied bleaching effects in 192 coral species living in water depths of three to 30 metres.

“We found great variation in the effects of bleaching between species, and overwhelming evidence that coral bleaching reduces as water depth increases,” Dr Muir said.

“We believe deep corals which are less susceptible to bleaching may be essential in minimising species extinctions and providing coral larvae to reseed damaged shallow reefs.

“In the Maldives we calculated the risk of extinction from bleaching for each of the coral species, finding several at high risk and three that already appear to be extinct in the area.” 

The researchers investigated differences in susceptibility for over 190 species of corals from 3 to 30 m depth, finding that the great majority of species had much lower bleaching damage in deeper waters. Photo: Paul Muir

Some corals adapting?

However, Dr Muir said the team was pleased to find some corals appeared to be adapting to increased water temperatures.

“Contrary to current belief, susceptibility to bleaching can vary quite widely within closely related coral species,” Dr Muir said.

“We discovered some highly resistant corals within three species normally considered very vulnerable to bleaching which suggests a small number of species may be able to adapt to rising sea temperatures.”

Queensland Museum’s Acting CEO Dr Jim Thompson said that the team was hoping to raise funds to return to the Maldives sites.

“The researchers want to conduct a similar study of Great Barrier Reef corals, and further investigate how deep corals may help reseed damaged reefs and assist them to become more resilient to bleaching,” Dr Thompson said.

This research published in Proceedings of the Royal Society was produced by Dr Paul R. Muir from Queensland Museum and UQ’s Global Change Institute, Associate Professor Paul A. Marshall from The University of Queensland, Dr Ameer Abdulla and Dr J. David Aguirre. The expedition was funded by the International Union for Conservation of Nature and USAID in collaboration with the Maldives Marine Research Centre.


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