Or, at least, they used to. “It’s all regulated by the environment,” Shlesinger says, “and when the environment is going through so much change, you’d expect that these processes will also change in response.”
Sure enough, Shlesinger and his colleague Yossi Loya have found that three common coral species in the Red Sea have lost their rhythm. Their timing is off; their unison is breaking. Rather than releasing a majestic unified blizzard of eggs and sperm at precise moments, they now spawn in pathetic, erratic drizzles across weeks and months. “It doesn’t look promising for those species,” Shlesinger says.
“This study is heartbreaking,” says Shayle Matsuda of the Hawaii Institute of Marine Biology. “This is something we’ve all worried might be true.”
Read: There is no escape for corals
“It’s definitely the case that the probability of fertilization goes way down if they don’t spawn at the same time, and really at the same time,” says Nancy Knowlton, a coral researcher at the Smithsonian National Museum of Natural History. There’s a huge evolutionary pressure for them to be synchronized, “so to not be synchronized is a really big thing.”
Shlesinger first realized something was wrong when he and Loya tried to rear some well-known coral species in large outdoor aquariums. To their surprise, some didn’t spawn at the expected times—an abnormality that Shlesinger initially blamed on his setup. “It took me two or three years to realize that things are completely off,” he says.
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.)