"I Saw 3 Live Corals In 45 Minutes" - Even Resilient Coral Reefs In French Polynesia Failing To Regrow Post-Bleaching
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In the middle of the South Pacific, 2,700 miles south of Hawaii, Moorea is known within the coral science community as an incredibly resilient place. But a new study has uncovered a peculiar phenomenon never before seen in scientific literature: hollowed-out dead corals are being structurally maintained by an encrusting algae. When corals die, a cycle begins. Usually, storms pass through that remove dead coral “rubble” from the seabed, creating a clean slate on which new corals can seed and grow. But in Moorea, these dead corals are held in place by a host of microscopic organisms, so even as storms pass through, the skeletons remain.
Since they aren’t breaking down, no new space is being created for coral to grow. Because corals face myriad climate-related threats, understanding how and why they aren’t recovering is crucial. Though this study marks the first documentation of this hollowing-and-scaffolding phenomenon, there is some anecdotal evidence of it happening elsewhere, including on nearby islands. If this is indeed regional, or even global, this study could be the first step towards restoring reefs like Moorea’s—that are stuck somewhere between life and death. Diving on these reefs today presents a sobering picture. The grey rubble of dead corals stretches as far as underwater visibility will allow. Every few hundred feet, a living coral can be seen hanging on. On one such dive, Hannah Stewart, head of science for the local nonprofit Coral Gardeners, was astonished. “I saw three live corals in 45 minutes,” she said. “It’s shocking.”
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On the outside, the encrusting red algae not only blanket the coral skeleton; their presence also drives the accretion of even more calcium carbonate from the seawater. “It’s like a natural cement that forms,” Fouke said. “And the problem with algae is that they are masters at biochemical warfare,” he said, able to produce enzymes, lipids and proteins that make the surface an inhospitable place for baby corals to land. Without a proper substrate to attach to, new corals have little hope of survival. The usual formula here includes coral mortality, the cycle of skeletons turning to rubble, that rubble getting cleared by storms and fresh substrate exposed for new corals. “But now this possibility for a reef to get stuck between the mortality and rubble formation phase has prolonged any sort of possibility of recovery,” Scafidi said.
The study is significant, said Edmunds, because it addresses how reefs degrade in a changing ocean. “Present-day reefs operate in a very different world of warmer seawater and more frequent storms,” Edmunds said, “so there is little reason to expect the old rules to apply to new situations.”In the South Pacific Ocean, fringing reefs encircle both volcanic islands and atolls, providing structural protection against storm surge and flooding. Islands like Moorea may survive if the reef dies, but without a coral reef, nearby low-lying atolls that rely on the reef for protection and sand replenishment could disappear beneath the sea.
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https://insideclimatenews.org/news/01062026/french-polynesia-coral-reef-bleaching/