The threat of climate change and warming oceans looms large over the world’s coral reefs, which are struggling to adapt to increasingly inhospitable waters. Scientists at the University of Pennsylvania have demonstrated a new way we may be able to limit the damage, by taking coral species that have already survived severe heat stress and transplanting them to degraded reefs to sow the seeds for restoration.
We are seeing a lot of focus from environmental scientists on how vulnerable corals can be made more resistant to heat stress. Some creative solutions include implanting them with helpful bacteria, developing more durable species through an innovative technique known as “directed evolution,” and feeding them probiotics to boost their chances of survival.
All of this is part of the effort to prevent the changes brought upon coral by abnormal sea temperatures, which causes algae living in their tissues to become stressed and break free. This leaves the coral without a key source of sustenance and causes them to turn white, whither, and in a lot of cases, die off, as seen in the bleaching events to plague Australia’s Great Barrier Reef in recent years.
The solution being explored by the University of Pennsylvania team focuses on coral that has already proved itself in the face of severe bleaching events. The scientists combed Hawaii’s coral reefs, which endured severe bleaching in 2015, in search of species that resisted the bleaching all together, with the intention of studying how they respond to being placed in an entirely different environment.
“The big thing that we were really interested in here was trying to experimentally test whether you an take a coral that seems to be resistant to climate change and use that as the seed stock to propagate and put out on a different reef that might be degraded,” says Katie Barott, who led the research team. “The cool thing was we didn’t see any differences in their bleaching response after this transplant.”
This is similar to strategies being explored at the Great Barrier Reef, where we have seen underwater robots reseed damaged areas with larvae captured during unpredictable coral blooms or turbo-charged larvae raised to have a higher thermal tolerance. This new research is designed to inform these kinds of strategies, by investigating whether transplanted coral collected from affected reefs can maintain their resilience after transplantation.
“If you take a coral that is resistant to bleaching in its native habitat, it could be that the stress of moving to a new place might make them lose that ability,” Barott says.
Factors like water flow rate, access to food and nutrients and light could all impact whether or not transplanted corals are as resilient as they were in their original habitat. To investigate these possibilities, the scientists gathered heat-resistant corals from two impacted reefs, one with a higher flow of water farther from shore and one closer to shore with more stagnant waters.
The heat-resistant corals were taken from one reef and transplanted to the other, while some were also placed in tanks where the scientists simulated bleaching events. The researchers tracked their health over six months after transplantation through metrics like photosynthesis rates, metabolism, calcification rates and the health of the algae, and found that they retained their resistance to bleaching.
“What was really novel is that we had this highly replicated experiment,” Barott says, “and we saw no change in the coral’s bleaching response.”
One thing that the experiments did appear to impact was the corals’ reproduction rates.
“The corals from the ‘happy’ site – the outer lagoon that had higher growth rates prior to the bleaching event – generally seemed a little happier and their fitness was higher,” Barott says. “That tells us that, if you’re going to have a coral nursery, you should pick a site with good conditions because there seems to be some carryover benefit of spending time at a nicer site even after the corals are outplanted to a less ‘happy’ site.”
While the findings bode well for the idea of targeting vulnerable reefs for seeding strategies, as is the case with other approaches to coral transplantation scaling these techniques up to address the broader problem isn’t a viable solution.
“I think techniques like this can buy us a little bit of time, but there isn’t a substitute for capping carbon emissions,” says Barott. “We need global action on climate change because even bleaching-resistant corals aren’t going to survive forever if ocean warming keeps increasing as fast as it is today.”
The research was published in the journal Proceedings of the National Academy of Sciences.
Transplanted coral retains resistance to heat in new environments [New Atlas]