Woods Hole broadcasts healthy-reef sounds to draw coral larvae onto damaged Caribbean reefs

Coral larvae can sense sound and use it as a cue while searching for a permanent home, and the Woods Hole project rests on that finding ^[4]. Taking it onto a degraded reef raises a design problem. A test of whether a speaker changes anything needs matched degraded sites with and without speakers, and a count of the young corals that settle at each. The Nature report does not say whether the Caribbean deployments include quiet control sites or how settlement will be counted ^[1]. "Healthy reefs are naturally broadcasting sound all over the place," said Aran Mooney, the WHOI marine bioacoustician who leads the project ^[5].

Sound acts on one step, the moment a larva picks a spot, and it does nothing about heat. Bleaching happens when corals expel the symbiotic algae they rely on for nutrients, and it can kill them ^[8]. This year's record ocean temperatures come from human-caused climate change and a super-strong El Nino brewing in the Pacific ^[7]. They are expected to rise further in 2027 as the El Nino reaches full strength ^[11]. Larvae settle permanently ^[1], so any recruit a speaker draws in this season will be fixed to that reef when the 2027 heat arrives ^[11]. "It's sort of like having COVID, also getting the flu, and at the same time being stressed about your job," said Amy Apprill, a marine geochemist who leads WHOI's coral-restoration team, of the stress that has built up on reefs ^[13].

Reefs can recover from bleaching, but recovery takes time ^[20]. Hot oceans have bleached corals worldwide four times since 1998 ^[16]. The 9.5% figure comes from an August report by hundreds of scientists comparing hard coral cover in 2020-2024 with 1980-2009 ^[17]. The same report found that 2024's record heat caused bleaching at nearly all the world's reefs and cut cover 8.9% from 2023, the largest single-year drop so far ^[18]. The first figure compares averages across decades and the second compares one year with the year before, so the two cannot be added into a single total loss ^[1]. "What that decline tells us is that the recovery is never enough before that decline happens again," said Manuel Gonzalez-Rivero, a report co-author at the Australian Institute of Marine Science ^[19].

NOAA's Coral Reef Watch found that large swathes of ocean had reached temperatures putting corals at risk of bleaching and heat mortality ^[10]. In my view the evidence supports a modest claim. More researchers are intervening directly this season ^[6], and programmes such as Coral Reef Watch still tell them where the heat is ^[10]. Michael Sweet, a coral biologist at the University of Derby, described the mood among researchers who have chosen to keep working. He said: "You swing between almost giving up, to going, 'I'm going to fight to my dying breath to try and make things a bit better'." ^[15]