In the Red Sea off the coast of Egypt, bottlenose dolphins barrel through a soft, bushy coral. Looks like fun, but maybe it’s medicine.
Dolphins may rub on specific corals and sponges to treat their skin, researchers reported Thursday in the journal iScience. These stationary sea creatures may serve as drive-by pharmacies, dispensing a chemical cocktail that could treat bacterial or fungal infections or support skin health. The scientists said that cetaceans have not been observed self-medicating before.
Angela Ziltener, a biologist, spotted this behavior in 2009. Dolphins lined up in front of a coral and each one took their turn, sometimes circling to the back of the line for another go. “It was very organized actually,” said Dr. Ziltener, who works at the Dolphin Watch Alliance in Switzerland.
The dolphins seemed to have clear preferences — out of hundreds of coral species in the reef, they used a select few, Dr. Ziltener said. Sometimes after the dolphins hit up a coral, their skin was stained yellow or green. Knowing that sponges and corals contain an assortment of chemical compounds, Dr. Ziltener connected with 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 exude.
During the summer of 2019, the researchers snipped tiny pieces from two soft coral and one sponge species they’d seen dolphins rubbing against in the Red Sea. Combining several powerful techniques, the team sleuthed for a range of substances. Dr. Morlock said they found a “potpourri” of 17 bioactive compounds, including antimicrobials, antioxidants and hormones.
Some of these molecules may serve as immune boosters or sunscreens, said Julia Kubanek, a marine chemist at the Georgia Institute of Technology who wasn’t part of the work. People have known about corals’ and sponges’ medicinal properties for around 50 years, she said.
“But dolphins may have known about how to use marine organisms as medicines 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 totally plausible,” said Eric Angel Ramos, a marine mammal scientist at the Rockefeller University in New York who was not part of this study. “But equally it’s plausible that they just love to rub against it.” Dolphin skin is very sensitive to touch, and contact plays a large role in how these animals interact with one another and their surroundings, he said.
He suggested testing whether the dolphins get a medicinal benefit from these invertebrates by working with captive animals. They often scratch, bite or otherwise beat up one another, which provides an opportunity to track how dolphins’ skin fares after some coral or sponge skin care.
The research team is working to analyze footage of thousands of dolphin rubs on corals and sponges from 2009 through 2021, Dr. Ziltener said. That data could contain clues to whether the dolphins are getting an Rx on the reef. For instance, if some of them repeatedly dose themselves, that could bolster the case for self-medicating. Tracking dolphins’ rubbing behavior could also reveal whether dolphins learn this behavior from one another, as the authors suggested.
“I’ve seen this exact behavior, and I didn’t think about it in those terms,” Dr. Ramos said. Though it might take years or decades to unravel whether dolphins self-medicate, he said, this study is opening a door to solve that mystery.