Corals Depend On Precise Timing To Reproduce; That's Now Disintegrating, And No One Knows Why
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Across 225 nights spread over four years, Shlesinger snorkeled through the Gulf of Eilat for hours, recording the number of spawning corals. Several species, he realized, had abandoned their regular year-on-year patterns. It’s not that they had shifted to a different time window. One of them spawned at a full moon in 2015, but at a new moon in 2016. Two others spawned in fits, on almost every night over several months. “They were completely unsynchronized,” he says. “Every night, I just saw a few individuals spawn, and they released just a few drops of material. It’s meant to blast into the ocean, but I just saw dribbles.”
On land, climate change has repeatedly screwed with nature’s schedules, making once-synchronized species out of step with each other. In parts of Alaska, brown bears are abandoning their usual feasts of salmon. Songbirds are struggling to feed their chicks as hatching periods become uncoupled from gluts of insects. Earlier snowmelts mean that snowshoe hares are becoming dangerously conspicuous as their still-white fur contrasts against exposed earth. Shlesinger’s work “supports the idea that natural patterns in the ocean are changing in similar ways to what we’ve observed on land,” says Erika Woolsey of the Stanford Center for Ocean Solutions.
The worst bit about this is that no one really knows why it’s happening. Light pollution from nearby cities could throw the corals off, as could plastics, pesticides, or human-made pollutants that resemble hormones. Then again, Shlesinger found that corals in isolated nature reserves had become just as desynchronized as those growing near urban areas. Whatever’s making them misfire is widespread in its reach, and rising temperatures seem like a likely culprit. “I wouldn’t be surprised if we hear about this phenomenon elsewhere in the next few years,” Shlesinger says. (Woolsey adds that scientists might be able to use crowdsourced data from dive-tour operators, Facebook groups, and apps like iNaturalist to check on coral-spawning patterns around the world.)
Read: Since 2016, half of the coral in the Great Barrier Reef has died
But even in the Red Sea, not all corals are affected. Some corals fertilize their eggs internally and release fully formed larvae, instead of spawning en masse. And among the mass-spawners, some are still keeping to their usual schedules. “It’s not that everything is going to hell,” Shlesinger says. But the species that have gone out of sync are already paying the price: For two species, Shlesinger couldn’t find a single juvenile. If that trend continues, those populations seem destined to age, and eventually disappear.
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https://www.theatlantic.com/science/archive/2019/09/great-spawning-corals-becoming-undone/597466/