Climate Change Remains a Threat to Corals

Hopes that coral reefs might be able to survive, and recover from, bleaching caused by climate change are fading for certain coral species, according to new research published by the University of Buffalo this week.

It shows, for the first time, that while hard corals can take up from the environment new stress-tolerant algae that provide critical nutrients, the coral may not be able to sustain the relationship with these algae over a long period. The findings may mean that certain types of coral will not be able to adapt rapidly enough to survive global warming, says the study’s lead author, Mary Alice Coffroth.

“Our findings suggest that not all corals can maintain a long-term symbiosis with these stress-tolerant strains of algae,” she says.

“That’s the problem,” Coffroth continues, “if they can’t take up the stress-tolerant symbionts, or if they take them up but can’t maintain the symbiosis with them, as we found, then they likely won’t be able to adapt rapidly enough to survive global warming.”

During the past two decades, Coffroth explains, coral reefs, known as the rain forests of the sea for their incredible biological diversity, have suffered bleaching events due to high water temperatures and light levels that cause them to literally “spit out” their algal symbionts, which provide their sustenance. Severe bleaching can lead to coral death.

In recent years, though, it has been reported that some corals appear to respond to rising sea temperatures by acquiring new stress-tolerant symbionts from the environment, which could allow them to survive the warmer oceans caused by climate change.

Coffroth says that the UB research shows that while the corals they studied were able to acquire new stress-tolerant symbiont strains from the water, they were unable to maintain that symbiosis for very long.

After about five weeks, the proportion of new symbionts within the coral had declined dramatically and after 14 weeks was no longer detectable in the corals.

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