Corals are bearing the brunt of the effects of global warming. The Australian Institute of Marine Science (AIMS) revealed in a new study on Tuesday (November 19) that the northern Great Barrier Reef recently suffered record mortality, never before recorded. The Australian government agency responsible for monitoring the reefs found that twelve of them recorded a decrease in coral cover of around 72%. In the northern region, around a third of corals have died in recent months.
The Great Barrier Reef, which stretches 2,300 kilometers along the coast of the state of Queensland (northeast Australia), is considered the largest living structure in the world. It is home to extremely rich biodiversity, with more than 600 species of coral and 1,625 species of fish.
The AIMS results are the first official assessment of the impact of the fourth global mass coral bleaching event, beginning in February 2023, which resulted in thermal stress high enough to bleach more than 70% of the planet's corals, affecting reefs in more than 70 countries.
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Bleaching occurs when corals are exposed to sources of stress such as temperature extremes or pH variations. In response, they expel symbiotic algae, zooxanthellae, which provide them with nutrients. This process turns corals white and deprives them of their main food source, compromising their survival.
“Very strong recurrence”
“If the stressful episode does not last long and does not repeat itself too often, the coral can survive”explains Lucie Penin, researcher in marine biology at the University of Réunion. But the rise in ocean surface temperatures leaves these colonies little respite. “There is a very strong recurrence of these bleaching events, which can sometimes come back at very short intervals, that is to say from one year to the next. This does not give the corals time to recover: they become fragile and end up dying”continues the specialist.
The Great Barrier Reef has experienced five episodes of mass bleaching in eight years, linked to ocean warming. A study published in Nature in August revealed that the water temperature in this region was higher in the last ten years than in the last four centuries.
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