Coral reefs may be more resilient to global warming than first thought, according to a study funded by NOAA. In fact the results suggest corals have already adapted to part of the warming that has occurred.
"Earlier work suggested that coral reefs would be gone by the middle of this century. Our study shows that if corals can adapt to warming that has occurred over the past 40 to 60 years, some coral reefs may persist through the end of this century," said study lead author Cheryl Logan, Ph.D., an assistant professor in California State University Monterey Bay’s Division of Science and Environmental Policy. The scientists from the university, and from the University of British Columbia, were NOAA’s partners in the study.
Warm water can contribute to a potentially fatal process known as coral "bleaching," in which reef-building corals eject algae living inside their tissues. Corals bleach when oceans warm only 1-2°C (2-4°F) above normal summertime temperatures. Because those algae supply the coral with most of its food, prolonged bleaching and associated disease often kills corals.
The study, published online in the journal Global Change Biology, explores a range of possible coral adaptive responses to thermal stress previously identified by the scientific community. It suggests that coral reefs may be more resilient than previously thought due to past studies that did not consider effects of possible adaptation.
The study projected that, through genetic adaptation, the reefs could reduce the currently projected rate of temperature-induced bleaching by 20-80% of levels expected by the year 2100, if there are large reductions in carbon dioxide emissions.
"The hope this work brings is only achieved if there is significant reduction of human-related emissions of heat-trapping gases," said Mark Eakin, Ph.D., who serves as director of the NOAA Coral Reef Watch monitoring program, which tracks bleaching events worldwide. "Adaptation provides no significant slowing in the loss of coral reefs if we continue to increase our rate of fossil fuel use."
"Not all species will be able to adapt fast enough or to the same extent, so coral communities will look and function differently than they do today," CalState’s Logan said.
In the study, researchers used global sea surface temperature output from the NOAA/GFDL Earth System Model-2 for the pre-industrial period though 2100 to project rates of coral bleaching.
Because initial results showed that past temperature increases should have bleached reefs more often than has actually occurred, researchers looked into ways that corals may be able to adapt to warming and delay the bleaching process.
The article calls for further research to test the rate and limit of different adaptive responses for coral species across latitudes and ocean basins to determine if, and how much, corals can actually respond to increasing thermal stress.
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