Six Months After Heat Spike, Bleached Caribbean Corals In Serious Trouble

In the northern hemisphere, the summer of 2023 was the hottest on record. In the Caribbean, coral reefs sat in sweltering water for months—stewing in a dangerous marine heatwave that started earlier, lasted longer, and climbed to higher temperatures than any seen in the region before. In some places, the water was over 32 °C—as toasty as a hot tub. Ever since the water started to warm, researchers and conservationists have been anxiously watching to see how the debilitating heat has affected the region’s corals.

For many Caribbean corals, last year’s heat proved too much to bear. The more time corals spend in hot water, the more likely they are to bleach, turning white as they expel the single-celled algae that live within their tissues. Without these symbiotic algae—and the energy they provide through photosynthesis—bleached corals starve. Survival becomes a struggle, and what had been a healthy thicket of colorful coral can turn into a tangle of skeletons.

In The Bahamas, where the shallowest reefs were hit particularly hard, Valeria Pizarro, a marine biologist at the Perry Institute for Marine Science, started to see some bleached corals recover in October and November of 2023, gradually regaining patches of color as symbiotic algae recolonized their still-living tissues. But as recently as January 2024, she and her team were still finding bleached corals that have yet to regain their algal allies. “Some days it’s just frustrating,” says Pizarro.

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Last summer’s extreme heat also bleached and killed nearly all of the corals within parts of the Mesoamerican Reef—the western hemisphere’s largest barrier reef system which stretches from the coast of Mexico’s Yucatan Peninsula south to Belize, Guatemala, and Honduras. At the Mexican end of the barrier reef, calm water near shore rose to 3 to 4 °C warmer than normal, causing widespread coral mortality. The same was true farther south, in a shallow lagoon of the barrier reef in northern Belize. While these shallow reefs suffered heavier losses, Álvarez-Filip says corals in the deeper reefs he surveyed also experienced widespread bleaching. Even 15 to 25 meters below the waves, “it was just bright white everywhere,” Álvarez-Filip says. “It was really hard to find a coral that was not bleached.”

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https://hakaimagazine.com/news/six-months-after-the-heat-spiked-caribbean-corals-are-still-reeling/