USC Coral Study Throws Coral Heat Tolerance Characteristics Into Question

USC marine scientists published a study this week that serves as a cautionary note for existing coral research and protection projects.

Assistant Professor of Biological Sciences Carly Kenkel led a team to study the endangered, near-shore mountainous star coral under the Caribbean Sea. The team wanted to understand the coral’s resistance to warmer temperatures and how the trait appeared in their offspring.

That question has been studied frequently within the Great Barrier Reef and reefs throughout the Pacific Ocean, but Kenkel wanted to see how those findings applied to reefs in the Caribbean Sea.

“We wanted to know was this tolerance something that they could pass on to their offspring, like to new baby coral,” Kenkel said. “So we set out to try to answer that question and honestly, we thought the answer was going to be yes.”

Turns out, not so much.

After a study in 2019, they found that the near-shore adults with higher tolerance spawned offspring that don't do as well in resisting heat.

“It's almost like training for a marathon,” Kenkel said. “The adults have trained and they've become more temperature tolerant because of that repeated stress. It seems like it's actually come at the cost of their ability to reproduce or make high quality offspring. They're investing in themselves, but that means they don't have anything left to give to their babies.”

The findings contrast commonly held notions among scientists that coral parents with heat tolerance breed the same trait in their offspring.

The researchers went back in 2021 and found not only the same response in heat-tolerant adults, but discovered another surprise — that less heat-tolerant adults bred offspring with higher tolerance.

Besides the impacts constantly high temperatures have on corals’ natural reproduction abilities, Kenkel worries that strategies implemented to help the coral, like selective breeding, rely on logic inconsistent with the study.

“Our data says you can't just assume that the more tolerant parents are going to produce more tolerant babies. That's something that really needs to be tested before going down the road of using those kinds of interventions for restoration,” Kenkel said.

Though her team was planning to study another species of Caribbean coral this past summer, the extreme heat killed off much of their population in question. She hopes the findings will at least start the conversations around whether the study applies to other species of coral and whether it is a dynamic that could become more normal with rising temperatures.

“I think there's lots of follow up questions that could be asked,” Kenkel said.