Safety in Numbers? Not So for Coral Amid Threat of Climate Change

Global changes in climate and ocean chemistry will affect coral reefs whether they are scarce or abundant, according to new research upending the traditional belief that corals do not face a risk of extinction unless they become very rare or have a very restricted range.

A team of scientists from University of Hawaii - Manoa (UHM), Joint Institute for Marine and Atmospheric Research (JIMAR) and the National Oceanic and Atmospheric Administration (NOAA) published their findings in the journal BioScience.

Based on an evaluation of the geologic record of past extinctions and recent events, the researchers were able to assess the characteristics of dominant corals under various conditions.

During periods advantageous to coral growth, the natural selection process favors coral with traits that make them more vulnerable to climate change, the scientists found.

"The last 10 thousand years have been especially beneficial for corals. Acropora species, such as table coral, elkhorn coral and staghorn coral, were favored in competition due to their rapid growth," the UHM said in a news release. "This advantageous rapid growth may have been attained in part by neglecting investment in few defenses against predation, hurricanes, or warm seawater. Acropora species have porous skeletons, extra thin tissue, and low concentrations of carbon and nitrogen in their tissues. The abundant corals have taken an easy road to living a rich and dominating life during the present interglacial period, but the payback comes when the climate becomes less hospitable."

The researchers suggest that the conditions driven by excess carbon dioxide ocean cause mortality at rates that are independent of coral abundance.

"This density-independent mortality and physiological stress affects reproductive success and leads to the decline of corals. Some coral species are abundant across a broad geographic range, but the new findings show that this does not safeguard them against global threats, including changing ocean chemistry and rising temperatures," the UHM researchers said.

Historically, assessments of the risk of extinction for a species of coral were made on the basis of how scarce or restricted in range it is. But the new findings highlight the vulnerability of abundant and widespread coral species as wells as species that are less prolific.

In future studies, the researchers said they hope to strengthen the case for directly addressing the global problems related to coral conservation.