Caribbean reefs have lost 48% of hard coral since 1980, study finds | Coral

Caribbean reefs now contain half as many hard corals as in 1980, a study suggests.

The 48% decrease in coral cover is due to climate change, in particular marine heat waves. They affect the microalgae that feed corals, making them toxic and forcing the coral to expel them.

In 2023-24, the region’s corals experienced “the most destructive thermal stress on record,” said Dr. Jérémy Wicquart of the Global Coral Reef Monitoring Network, one of the study’s editors. This resulted in a decrease in coverage of 16.9% year-on-year.

Forty years ago, a diver would have seen a colorful and vibrant ecosystem that supported hundreds of marine species such as lobsters, conchs, parrotfish, turtles and sharks. Coral reefs cover less than 1% of the planet’s seabed, but are home to at least 25% of marine species.

But when Wicquart went diving last year after a conference in Puerto Morelos, Mexico, he encountered white, dying coral.

“All the corals were bleached. All the corals were white. I was very affected by that. It’s totally different when you see it in the field than when you see it on a graph.”

The bleaching effect is due to the loss of essential microalgae, which nourishes stony corals and gives them their color. Without these microalgae, hard coral can recover, but is more likely to die. The destruction is exacerbated by cyclones that shake the coral, turning it into rubble on the ocean floor.

Caribbean coral reefs generate $6.2 billion (£4.6 billion) a year from fishing and tourism, with reef tourism accounting for 10% of Caribbean GDP.

But where there was once coral, macroalgae thrive. Without competition from coral, its cover has increased by 85% since 1980. Its growth is favored by human activities in the area – overfishing of their herbivorous predators in particular.

The study, which was carried out by more than 300 scientists in 44 countries and territories, also highlights conservation successes that provide hope for the future. The southern Gulf of Mexico has been facing severe heat stress since 2023, yet researchers there have discovered ancient coral colonies that are resilient, disease-free, and contain critically endangered coral species.

As a result, the Mexican government created a new marine protected area in the Gulf that connects two existing national parks. Together they form a continuous corridor of reef habitats that allow corals and reef species to thrive.

“The science is unequivocal, but it also brings hope. When pressures ease and resources are supported, Caribbean reefs bounce back,” said Sinikinesh Beyene Jimma, head of the marine and coastal ecosystems department at the United Nations Environment Program.

The coral reefs of the Caribbean are unique because of the human density that surrounds them. The number of people living within 20 km of coral reefs has increased by 27.6% since 2000.

This means that reefs are more sensitive to local human activity, in addition to human-induced climate change. It also means people have the opportunity to restore reefs with the right management techniques.

“If you act on climate change, you will reduce heat stress on coral reefs and the impact of cyclones. The second major solution is to reduce local threats. You can improve water quality by implementing better wastewater management. You can restrict mass tourism and create marine protected areas. These are ways to improve coral reefs on a local scale,” Wicquart said.