A new study shows that corals in the north of the Great Barrier Reef experienced a catastrophic death following the 2016 marine heat wave. “When corals are bleached from a heat wave, they can survive and recover their colour slowly, as the temperature goes down, or they can die. ”
Averaged across the Great Barrier Reef, Professor Terry Hughes, director of the ARC Center for Excellence in Coral Reef Studies (Coral CoE) in Australia, says that 30 percent of corals were lost in the nine-year period months between March and November 2016.
The scientists, whose work is published in Wednesday’s digital edition of ‘Nature’, mapped the geographic pattern of heat exposure from satellites and measured coral survival along the 2,300-kilometer long Great Barrier Reef. of Coral after the extreme marine heatwave of 2016. The amount of coral death that they measured was closely related to the amount of whitening and the level of exposure to heat, with the northern third of the Great Barrier Reef being the most severely affected.
The study found that 29 percent of the 3,863 reefs that make up the world’s largest reef system lost two-thirds or more of their corals, which transformed the ability of these reefs to maintain full ecological functioning.
“The extinction of corals has led to radical changes in the mix of coral species in hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with only a few remaining hard species,” says the co-author Andrew Baird, of Coral CoE at James Cook University.
“As part of a global coral bleaching event that covered 2014-2017, the Great Barrier Reef underwent severe heat stress and discoloration again in 2017, this time affecting the central region of the Great Barrier Reef,” says co-author Mark Eakin, of the National Oceanic and Atmospheric Administration of the United States.
A CALL TO CORAL AUXILIARY
“Now, we are at a point where we have lost about half of the corals in shallow water habitats in the northern two-thirds of the Great Barrier Reef due to subsequent bleaching in two consecutive years,” says Professor Sean Connolly, from Coral CoE at James Cook University.
“But that still leaves one billion live corals and, on average, they are more resistant than those that died, we have to urgently concentrate on protecting the glass that is still half full, helping these survivors to recover,” Professor Hughes proposes.
Scientists say these findings reinforce the need to assess the risk of a large-scale collapse of reef ecosystems, especially if global action on climate change does not limit warming to 1.5-2 degrees above pre-industrial levels. The study tests the emerging framework of the Red List of Ecosystems of the International Union for the Conservation of Nature (IUCN), which seeks to classify vulnerable ecosystems as “safe”, “threatened” or “endangered”.
“The Great Barrier Reef is really threatened by climate change, but it is not doomed if we quickly address greenhouse gas emissions.” Our study shows that coral reefs are already changing radically in response to unprecedented heat waves. , warns Professor Hughes.
The researchers warn that if climate change is not curbed, causing the global temperature to rise by much more than 2 degrees, the tropical reef ecosystems will be radically altered and the benefits they provide to hundreds of millions of people will be impaired, mainly in countries poor and rapidly be developing.