October 30, 2013
A Changing Climate May Not Spell Doom For Coral Reefs After All
April Flowers for redOrbit.com - Your Universe Online
A new study from the National Oceanic and Atmospheric Administration (NOAA) and its academic partners reveals that coral reefs may be able to adapt to moderate climate warming, improving their chance of surviving through the end of this century, if there are large reductions in carbon dioxide emissions.The findings, published online in the journal Global Change Biology, also suggest corals have already adapted to part of the warming that has occurred.
"Earlier modeling 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 Cheryl Logan, PhD, an assistant professor in California State University Monterey Bay's Division of Science and Environmental Policy.
Warm water contributes to "coral bleaching," a potentially fatal process in which reef-building corals eject algae living inside their tissues. When oceans warm just 2-4 degrees Fahrenheit above normal summertime temperatures, coral bleaching occurs. Prolonged bleaching, and the associated disease, often kills corals because the dying algae supply the coral with most of its food.
The research team explored a range of possible coral adaptive responses to thermal stress previously identified by the scientific community, which suggested that coral reefs may be more resilient than previously thought due to past studies that did not consider effects of possible adaptation. Through genetic adaptation, the researchers project that the reefs could reduce the currently projected rate of temperature-induced bleaching by 20 to 80 percent 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, PhD, 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," Logan said.
Previous studies have documented many other general threats to coral species that affect their long-term survival, including coral disease, acidification, and sedimentation. Additional threats include sea-level rise, pollution, storm damage, destructive fishing practices, and direct harvest for ornamental trade.
According to the Status of Coral Reefs of the World: 2000 report, issued by the International Coral Reef Initiative, coral reefs have been lost around the world in recent decades. High temperatures during the 1998-1999 El Nino and La Nina killed nearly 20 percent of global reefs, and an 80 percent loss of coral cover in the Caribbean was documented in 2003. Many subsequent studies have documented these losses.
Among the most diverse ecosystems in the world, tropical coral reef ecosystems provide economic and social stability to many nations in the form of food security, where reef fish provide both food and fishing jobs and revenue from tourism. Over the last 30 years, mass coral bleaching and reef death has increased around the world, raising questions about the future of coral reef ecosystems.
The research team used global sea surface temperature output obtained from the NOAA/GFDL Earth system Model-2. This model allowed the team to project rates of coral bleaching from the pre-industrial period through 2100.
The initial results revealed that past temperature increases should have bleached reefs more often than has actually occurred. Because of this, the research team investigated ways that corals may be able to adapt to warming and delay the bleaching process.
Further research is needed 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.