Half of the corals of the Great Reef in Australia have perished in the past 25 years, scientists said Wednesday, warning that global warming is irreversibly disrupting this underwater ecosystem.
A study published in the scientific journal Proceedings of the Royal Society sounds the alarm on the extent of the decline of all types of corals since the mid-1990s at the site in northeastern Australia, listed in 1981 as a Unesco World Heritage.
The largest species of coral – especially table-shaped and branched ones – have been the most affected, to the point where some of them have disappeared from the northernmost part of the Great Reef.
“They are 80 or 90% disappeared compared to 25 years ago,” James Cook University professor Terry Hughes, one of the study’s authors. “They offer the nooks and crannies that many fish and creatures take refuge in, and losing these huge three-dimensional corals will change the whole ecosystem.”
Besides its invaluable natural or scientific point of view, it is estimated that the coral reef, which stretches over 2,300 kilometers in length, generates four billion dollars in revenue for the Australian tourism sector.
The Great Barrier could lose its World Heritage status, due to its degradation which is largely due to the recurrence of episodes of coral bleaching, which is the consequence of climatic upheavals.
Coral bleaching is a process in which corals lose their characteristic color due to the extinction of the symbiotic microalgae, which coexist with them, this extinction being due to changes in ocean water. Algae acquire almost 90% of their energy through photosynthesis, which is why bleaching leads to the death of some coral species. The phenomenon occurs primarily because of changing ocean temperatures, bacteria causing disease, pollution, and ocean acidification linked to greenhouse gas emissions into the atmosphere.
During the 1980s, almost all of the major coral regions (Western Atlantic Ocean, Caribbean Sea, Pacific Ocean, Indian Ocean, Arabian Penisula and Red Sea) recorded bleaching. Since the 1990s, bleaching has worsened and spread, killing many corals.