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Corals can be trained to endure heat stress

A new study led by the University of Miami’s Rosenstiel School of Marine and Atmospheric Science has found that a stressful temperature treatment in the laboratory for 90 days can make corals more tolerant to increased water temperatures.

Since global warming is the greatest threat that coral reefs currently face, these findings can offer restoration scientists new approaches to increase the success rate of planting new, more resilient coral onto degraded reefs as climate change continues to increase water temperatures.

While previous “stress-hardening” experiments have exposed corals to short-term higher temperatures, this new study assessed the effect of a long-term, variable treatment, where temperatures were increased to a stressful level for a brief period of time, twice per day.

“This ‘training’ regime is akin to an athlete preparing for a race,” said study lead author Allyson DeMerlis, a Ph.D. candidate at the UM Rosenstiel School. “We were able to demonstrate that this temperature treatment can boost the corals’ stamina to heat stress.”

DeMerlis and her colleagues collected fragments from six distinct genetic individuals of Caribbean staghorn coral from the UM Rosenstiel School’s Rescue a Reef coral nursery and randomly assigned them to three groups: field control, laboratory control, and variable temperature treatment.

While the laboratory control corals were kept at a constant 28 degrees Celsius for a period of three months, the variable temperature treatment corals were exposed twice per day to fluctuating temperatures between 28 and 31 degrees Celsius.

The scientists measured bleaching progression and the number of days that corals endured thermal stress before bleaching. They found that the variable temperature treatment significantly improved tolerance to thermal stress. Moreover, untreated corals were more prone to succumb to disease-like signs of tissue loss.

These results prove the benefits of using such methods to increase corals’ thermal endurance, and could be applied in the field by restoration practicians in order to identify locations where their nurseries and outplanting sites could be exposed to higher, fluctuating temperatures.

“We have unfortunately reached the point where active intervention and restoration are necessary to ensure that valuable coral reefs are able to persist for generations to come,” said study senior author Ian Enochs, a coral scientist at the National Oceanic and Atmospheric Administration (NOAA). “We want to increase the efficiency and efficacy of these efforts, and ultimately ensure that the corals that are placed back out on a reef have the greatest chance of enduring the stressful conditions they will face in the future.”  

“Our findings bring a glimmer of hope to the uncertain future of corals, as we identified a treatment in which we can enhance their tolerance to heat stress,” concluded DeMerlis.

The study is published in the journal Coral Reefs.

By Andrei Ionescu, Staff Writer

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