Corals that withstood a severe bleaching event and were transplanted to another reef retained their resilient properties, according to a new study led by Katie Barott of the University of Pennsylvania
Photo credit: S. Matsuda
In 2015, almost half of Hawaii’s coral reefs were hit by the worst bleaching event to date. Coral bleaching occurs when warmer than normal ocean temperatures cause corals to drive away the algae that normally live in them and that the corals rely on for food.
Bleaching events are terrifying, but corals can sometimes recover while others resist bleaching altogether. In a new study in the journal Proceedings of the National Academy of Sciences, Researchers led by Katie Barott from the University of Pennsylvania found that these battle-hardened, resilient corals can thrive even if they are transplanted to a different environment and subjected to additional heat stress. The results give hope that robust corals could serve as a foundation population for reef restoration in the future.
“The big thing that really interested us here was trying to test experimentally whether you could take a coral that appears to be resistant to climate change and use it as a seed store to multiply and relocate to another reef that may have been degraded. ”“ says Barott. “The cool thing was that we didn’t see any differences in their bleaching response after this transplant.”
Mass coral bleaching is becoming more common, raising concerns that corals will become victims of climate change in the near future. However, Barott and colleagues have studied the corals that resist bleaching to buy corals more time to hold out in the face of the warming and acidification of ocean waters.
One strategy that she and others have envisioned and tried in areas like the Great Barrier Reef is coral transplantation. Researchers could replenish reefs damaged by climate change – or other anthropogenic attacks such as sedimentation or the run-up of a ship – with corals that have proven to be robust and can survive in the face of harsh conditions.
For this to work, however, the “survivors” of the corals would have to continue to show their resilient properties after being moved into a new environment.
“If you take a coral that is resistant to bleaching in its natural habitat, the stress of moving to a new location could cause it to lose that ability,” says Barott.
Just as a fern grown well in the shade can wither if moved to sunny property, so too can the conditions of a new environment, including water flow, food access, light, and nutrient availability, affect the resilience of the transplanted coral.
Barott and colleagues investigated this question with an experiment on two reefs in Hawaii’s Kaneneohohe Bay on the island of O? Ahu: one closer to the shore with more stagnant waters and another further away from the coast with higher currents. In each area, researchers identified coral colonies that had resisted bleaching during the 2015 bleaching event and collected samples from them the following year. Corals are clonal organisms, so a piece of a colony can grow back and have the same genetics as the “mother” coral. For each colony, they kept some samples on their home reef and transplanted others to the second reef.
After the corals had spent six months in their new location, the biologists also filled coral samples from each location into tanks in the laboratory and simulated further bleaching by increasing the water temperature over several days.
The team carefully tracked coral health and environmental conditions, measuring rates of photosynthesis, metabolism and calcification rates, and the health of the symbiotic algae. They found that bleach-resistant corals stayed that way in a new environment.
“The really new thing was that we had this highly replicated experiment,” says Barott, “and we didn’t see any change in the coral’s bleaching response.”
The researchers also looked at how well the corals reproduced in the summer after they were collected. The natural site conditions of a coral had an impact on its future reproductive ability, they found.
“The ‘happy’ site corals – the outer lagoon, which had higher growth rates before bleaching – generally appeared a little happier and their fitness levels were higher,” says Barott. “This tells us that if you want a coral nursery you should choose a location with good conditions, as there seems to be some benefit in spending time in a nicer location, even after the corals have been planted in a less planted location were. “happy side.”
The “lucky” spot, the lagoon farther from the shore, had higher flow rates than the other reef, which is closer to the shore, less salty and more stagnant. “Higher flow rates are really important in helping corals get rid of waste and get food,” says Barott.
Barott, who started as a postdoctoral fellow at the Hawaii Institute of Marine Biology, continues her research on coral resilience at her laboratory in Penn, including a study of the effects of heat stress and bleaching on reproductive success and function of coral sperm.
The results of the transplant study are promising, but they are only a temporary solution to the impending climate change.
“I think techniques like this can buy us a little bit of time, but there is no substitute for limiting carbon emissions,” she says. “We need global action against climate change, because even bleach-resistant corals will not survive forever if ocean warming increases as fast as it does today.”
Katie L. Barott is an Assistant Professor in the Department of Biology at the University of Pennsylvania School of Arts & Sciences.
Barott’s co-authors on the work were Penns Teegan Innis and Ariana S. Huffmyer of the University of Hawaii, Jennifer M. Davidson, Elizabeth Lenz, Shayle B. Matsuda, Joshua R. Hancock, Crawford Drury, Hollie M. Putnam, and Ruth D. Gates.
The study was supported by the Paul G. Allen Family Foundation, the University of Pennsylvania, and the National Science Foundation (grants 1923743 and 1323822).
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