The disappearance of the largest coral reef on the planet is accelerating at an unprecedented speed. The continuing loss of adult corals from global warming does not allow new corals to develop. The study Global warming impairs stock-recruitment dynamics of corals has revealed that, compared to the average of the last 20 years, the number of new larvae has been reduced by 93% in 2018. In 2017 it was 89%.
The figures are alarming. "Recruitment, (that is, when the larvae settle on a coral reef) varies from year to year, but the decline of 2018 is unprecedented," says Terry Hughes, author of the report and Director of the Coral Reef Studies Center at James Cook University from Queensland, Australia.
The average number of births in each reef has undergone a drastic change in 20 years, but especially after coral bleaching or bleaching of 2016 and 2017. The heating of the water causes some corals to expel zooxanthellae (the algae that give them their color), and acquire a whitish tone. Once the loss of tonality begins, it tends to continue (even if the temperature recovers). If the coral colony survives the period of thermal stress, zooxanthellae take months or years to recover. In the case of the Great Barrier "it will take between five and 10 years for a recovery of recruitment to occur." We are very concerned that the repair may be interrupted or reversed if another mass whitening occurs, "says Hughes.
The team of Coral Reef Studies Center at James Cook University has measured the amount of adult corals on the reefs before and after the discoloration. They calculated the length of the corals and identified each species. "We measure the number of baby corals each year by providing a surface for them to settle." The team placed 1,000 panels that were fixed to the reefs along the 2,300 km of the Great Barrier Reef, just before the annual spawning of the corals, and they were collected after eight weeks. In this way they obtained an estimate of the larval supply of the reef.
The great barrier is found in the Coral Sea, facing Queensland (northeast of Australia) and forms a line parallel to the coast but discontinuous. It consists of more than 2,000 individual reefs, around 1,000 islands and can be seen from space. It begins near latitude 9 ° S, south of Papua New Guinea, and continues southeast until latitude 24 ° S, although its exact extent has not been delimited.
It is essential to reduce emissions drastically, especially CO2, and the only way is with a radical change in the energy model
Experts agree that the only way to save this natural wonder that agluitina one of the largest concentrations of biodiversity on the planet is to curb global warming through a reduction in emissions of greenhouse gases. "It is essential to drastically reduce emissions, especially CO2, and the only way to achieve this is by making a radical change in the energy model through a rapid transition to renewable energies," says Carles Pelejero, a researcher in Marine Biology and Oceanography. at Institut de Ciències del Mar (ICM), in Barcelona. "The longer we take to react, the more aggravate the problem," adds Pelejero.
New ways of recovery
Some reefs of the Great Barrier have disappeared or are about to become extinct and it is not viable to try to recover them. However, there are initiatives to try to save some of them. Australian researcher Ove Hoegh-Guldberg focuses on the reefs that have more favorable health conditions with the initiative 50 Reefs. Its intention is to protect some reefs from the stress factors that affect these ecosystems, (in addition to temperature, pollution, overfishing or coastal development). "These protected reefs could serve as coral nurseries to later transplant them to other reefs and restore coral reef cover," explains Pelejero.
Other researchers across the globe are proposing biotechnological options for repopulation such as assisted gene flow through the transplantation of coral varieties adapted to warmer conditions. For example, the transfer of species from the Persian Gulf to the reefs of the Great Barrier Reef, so that they mix with native corals transmitting their genes to improve tolerance to high temperatures.
"They are not miraculous measures nor will they manage to save the Great Barrier in the long term if we do not slow down global warming," says Andrew Baird, a coral reef researcher at the James Cook University of Australia. "If there are more bleaching, the reef will change, but it will not be completely destroyed for centuries," he says.
Coral reefs are unique ecosystems, rich in biodiversity. That is, its structures house a large number of organisms (it is estimated that 25% of marine species live in association with coral reefs). As the corals of a reef die, the community of organisms that live there diminishes their diversity. "Corals are the engineers of the reef ecosystem. Without corals there would be no reef or associated fauna, "concludes Baird.