In the Red Sea off the coast of Egypt, bottlenose dolphins walk through soft, dense coral. It seems nice, but maybe it’s a drug.
Dolphins can rub on specific corals and sponges to treat their skin, researchers reported Thursday in the journal iScience. These stationary marine creatures can serve as drive-by pharmacies, releasing a chemical cocktail that can treat bacterial or fungal infections or support skin health. The scientists said cetaceans have not been observed self-medicating before.
Angela Ziltener, a biologist, saw this behavior in 2009. Dolphins lined up in front of a coral and each took their turn, sometimes circling to the back of the line for another try. “It was actually very organized,” says Dr. Ziltener, who works at the Dolphin Watch Alliance in Switzerland.
The dolphins seemed to have clear preferences — of the hundreds of coral species in the reef, they used a select few, said Dr. more salty. Sometimes after the dolphins hit a coral, their skin was yellow or green. Knowing that sponges and corals contain an assortment of chemical compounds, Dr. Ziltener contacted Gertrud Morlock, an analytical chemist at Justus Liebig University Giessen in Germany, to investigate whether the dolphins’ behavior could be explained by what’s in the goo these creatures secrete.
In the summer of 2019, the researchers cut small pieces from two types of soft coral and a sponge that they had seen dolphins rubbing against in the Red Sea. Combining several powerful techniques, the team searched for a range of fabrics. dr. Morlock said they found a “potpourri” of 17 bioactive compounds, including antimicrobials, antioxidants and hormones.
Some of these molecules could serve as immune boosters or sunscreens, said Julia Kubanek, a marine chemist at the Georgia Institute of Technology who was not part of the work. People have known about the medicinal properties of corals and sponges for about 50 years, she said.
“But dolphins may have known how to use marine organisms as medicine for much longer than we have,” she said.
Still, she noted that the scientists didn’t report whether dolphins prefer to rub against corals and sponges that contain more bioactive compounds.
Self-medication “seems perfectly plausible,” said Eric Angel Ramos, a marine mammal scientist at Rockefeller University in New York who was not part of this study. “But it’s equally likely that they just like to rub it.” Dolphins’ skin is very sensitive to touch, and contact plays a big role in how these animals interact with each other and their environment, he said.
He suggested testing whether the dolphins get a medicinal benefit from these invertebrates by working with animals in captivity. They scratch, bite or otherwise beat each other up, providing an opportunity to monitor how dolphins’ skin is doing after some coral or sponge skin care.
The research team is analyzing images of thousands of dolphin rubbings on corals and sponges from 2009 to 2021, said Dr. more salty. That data could provide clues as to whether the dolphins are getting an Rx on the reef. If some of them dose themselves repeatedly, it could reinforce the reason for self-medication. Tracking dolphins’ rubbing behavior could also reveal whether dolphins learn this behavior from each other, as the authors suggested.
“I’ve seen this exact behavior and I haven’t thought about it in those terms,” said Dr. Ramos. While it could take years or decades to unravel whether dolphins self-medicate, he said, this study opens a door to solving that mystery.