Helping Corals Beat The Heat

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Helping Corals Beat The Heat

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Climate change means coral populations in our seas are threatened by warming sea temperatures. A new study has found a way to help corals beat the heat.

US scientists have discovered that coral – the tiny creatures that bring colour and life to submerged reefs in the world’s oceans – can be trained to tolerate increases in temperatures.

The discovery has profound implications for ecology and maritime conservation across the world as climate change threatens the future of vastly disparate temperature-sensitive coral populations.

The study, conducted by researchers at the University of Miami in the United States, revealed that corals that endured a stressful laboratory-controlled temperature treatment lasting three months were more tolerant to increases in water temperatures.

Increasing water temperature sits at the heart of threats to the future of famous coral populations such as the great barrier reef off the Eastern coast of Australia.

The findings hold out fresh hope to coral restoration scientists by providing a fresh approach to potentially increase the success rate of planting nursery-raised staghorn coral onto degraded reefs as climate change continues to warm ocean temperatures

It is these temperature variations that cause widespread bleaching events. Staghorn coral – scientific name Acropora cervicornis – has died off throughout South Florida in US waters and the Caribbean and is listed as “threatened” on the US Endangered Species Act.

There are approximately 160 species of staghorn corals worldwide. Staghorn corals are believed to have evolved around 55-65 million years ago and have proliferated in many reefs during the past 500,000 years.

Staghorn coral is also one of the most common species of coral found on the Great Barrier Reef, emphasising the international implication of the new study in the fight against the impacts of climate change.

While previous “stress-hardening” experiments on corals have employed exposure to short-term temperatures, the University of Miami team assessed the effect of a long-term, variable treatment where temperatures reached a stressful level for a brief period, twice per day.

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

Corals showing healthy coloration at the beginning of the heat-stress test. Photos such as this were taken daily in order to track the progression of bleaching during the tests. Photo Credit: Amanda Kirkland

Allyson and her team collected coral fragments from six distinct genetic individuals of Caribbean staghorn coral and randomly assigned them to one of three groups: (1) field control, (2) laboratory control, and (3) variable temperature treatment.

The tests were conducted over a three-month treatment period.

Laboratory controls were kept at 28 degrees Celsius, while the changing temperature regime corals were introduced to intermittent temperatures between 28 to 31 degrees Celsius twice each day.

The intermittent treatment significantly improved coral endurance during thermal stress, often by as much as several days, in comparison to the untreated corals.

Moreover, they found that untreated corals were more likely to succumb quickly to disease-like signs of tissue loss.

Reef restoration scientists may in the future be able to translate these findings in the field by identifying locations where coral nurseries can be exposed to more 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,” says Ian Enochs, a senior study author and a coral scientist at the US Atlantic Oceanographic and Meteorological Laboratory.

“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.”

Allyson DeMerlis says the 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.”

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