As climate change makes the ocean hotter, marine heat waves are causing coral bleaching—when a healthy, colorful reef suddenly expels algae. The reef turns white, and tiny coral polyps, which had been living symbiotically with the algae, risk disease and starvation. If the stress continues too long, the corals die.
Probiotics designed for coral reefs might be able to help. In a new study, scientists simulated a heat wave in aquariums, pushing the temperature of the water up to 86 degrees for 10 days. In some of the tanks, fragments of coral reefs were dosed with a mix of beneficial bacteria. Others were sprayed with a placebo dose of saline. All of the corals that got the probiotics survived. Forty percent of the corals in the other group died.
“We are using native bacteria that are very abundant in the reef,” says Raquel Peixoto, a marine science professor at Saudi Arabia’s King Abdullah University of Science and Technology and one of the authors of the study. Climate change can disrupt that balance. She compares the process of rebuilding the ecosystem of microorganisms to reforestation. “We are trying to reboot this microbiome by replacing these bacteria,” she says.
While it’s easy to add probiotics inside a tank, it will be more challenging in the ocean. “Just dropping microbes in or even putting them on the surface of the coral gives you a very low probability” of them attaching to the coral, says Raja Dhir, cofounder of Seed Health, a startup now partnering on the project. The company, which also makes probiotics for humans and a probiotic designed to help bees better resist the effects of pesticides, is helping study various methods of delivery. One option might be something like a nicotine patch. “One side is a gel-like material which mimics the mucus of the coral,” Dhir says. The patch would slowly release a dose of probiotics directly onto the coral. Peixoto says that the team is also exploring the robots that could help scale up coverage more quickly. Projects that farm coral to replant in the ocean could also boost their baby corals with probiotics, which could have a second benefit of helping the corals grow faster.
Before the process is used in the ocean, there will be more lab tests to see the impacts on a wider range of coral species, and then pilot tests in small areas of reefs. Dhir argues that the world needs to act quickly, while taking precautions to make sure that the probiotics don’t unintentionally introduce new problems. “We take the stance that if it’s human-induced behavior which is causing the decline of these ecosystems, then we have a moral imperative to intervene in the most fragile of those ecosystems if we know we can do so safely and efficaciously,” he says.
The bacterial cocktails can be used in combination with other strategies, such as breeding corals to resist heat. But the most critical step is reducing emissions: If climate change continues on its current path, coral reefs won’t survive. Probiotics might help buy more time now, but aren’t a complete solution. “We need to work on the only solution, which is CO2 mitigation,” says Peixoto. “And in addition, we need to develop some strategies to accelerate adaptation.”