Treatment options for coral reefs stricken with tissue loss diseases often involve antibiotic treatments that can have an adverse impact on the surrounding environment and can lead to increased antibiotic resistance. 

An international team of researchers have developed an alternative treatment in the form of a paste made from chlorine and cocoa butter. Their findings were recently published in the Frontiers in Marine Science journal. 

Studying the corals at Horseshoe Reef

To evaluate the effectiveness of the alternative treatment, researchers travelled to the coral reefs of Horseshoe Reef, near the British Virgin Islands. There, they treated one group of diseased corals with amoxicillin, an antibiotic, and another group with a paste that was made from chlorine and cocoa butter. 

The active ingredient in the paste was sodium hypochlorite, an antiseptic used to kill bacteria or viruses. The chlorine powder was the same used for cleaning swimming pools, and the cocoa butter was the delivery mechanism used to spread the chlorine on the coral lesions.

Both treatments were applied directly to the corals. The researchers revisited the corals every four to five weeks to monitor and record their condition, and to reapply the treatment as necessary.

According to a press release, after about 80 days, “the median percentage of tissue lost was 17.6 percent for chlorine-treated colonies and 1.7 percent for amoxicillin-treated colonies.”

Environmentally friendly

Although the antibiotic treatment was more effective in treating the corals, this was outweighed by the adverse effects, like developing bacteria that was resistant to antibiotics. If this happened, it was not only corals that would be affected. “Any organism—crabs, fish, even humans—in that same environment has a higher risk of encountering bacteria that are now antibiotic-resistant,” cautioned Aeby.

In contrast, the chlorine and cocoa butter paste was natural and biodegrades easily, with the chlorine deactivating naturally within a day. This contrasted with the antibiotic treatment, which required substances that were expensive and tedious to produce.

More to be done

However, not all coral species responded equally well to the new treatment. More research was needed to test the effectiveness of this treatment method on the coral species in the other regions of the world.

Senior author Dr Greta Aeby, a researcher at Qatar University, also highlighted that directly treating the disease—by hand and individually—would not remove the disease from the coral population at large and was not feasible in the long term.

“The best strategy would be to improve environmental conditions so that corals have a better chance of fighting disease themselves. This includes cleaning up water pollution and rebalancing the ecosystem,” she said.