Hawaiian corals show surprising resilience to warming oceans

A long-term study of Hawaiian coral species provides a surprisingly optimistic view of how they might survive warmer and more acidic oceans resulting from climate change.

Researchers found that the three coral species studied did experience significant mortality under conditions simulated to approximate ocean temperatures and acidity expected in the future — up to about half of some of the species died.

But the fact that none of them completely died off — and some actually were thriving by the end of the study — provides hope for the future of corals, said Rowan McLachlan, who led the study as a doctoral student in earth sciences at The Ohio State University.

“We found surprisingly positive outcomes in our study. We don’t get a lot of that in the coral research field when it comes to the effects of warming oceans,” said McLachlan, who is now a postdoctoral researcher at Oregon State University.

The study lasted 22 months, which is much longer than most similar research, which often spans days to up to five months, Grottoli said.

Rising levels of carbon dioxide in the atmosphere have led to warmer oceans and about a quarter of the carbon dioxide in the air dissolves into the ocean, causing it to become more acidic. Both rising acidity and temperatures threaten coral, Grottoli said.

In this study, the researchers collected samples of the three most common coral species in Hawaii: Montipora capitataPorites compressa and Porites lobata.

The samples were placed in tanks with four different conditions: a control tank with current ocean conditions; an ocean acidification condition (-0.2 pH units); an ocean warming condition (+2 degrees Celsius); and a condition that combined warming and acidification.

Results showed that warming oceans will hurt coral species: 61% of corals exposed to the warming conditions survived, compared to 92% exposed to current ocean temperatures.

The two Porites species were more resilient than M. capitata in the combined warming and acidification condition. Over the course of the study, survival rates were 71% for P. compressa, 56% for P. lobata and 46% for M. capitata.

“Of the coral that survived, especially the Porites species, they were coping well, even thriving,” McLachlan said. “They were able to adapt to the above-average temperature and acidity.” For example, the surviving Porites were able to maintain normal growth and metabolism.

Journal Reference:

  1. McLachlan, R.H., Price, J.T., Muñoz-Garcia, A. et al. Physiological acclimatization in Hawaiian corals following a 22-month shift in baseline seawater temperature and pHScientific Reports, 2022 DOI: 10.1038/s41598-022-06896-z

Ohio State University (via ScienceDaily), 10 March 2022. Press release.

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