If a human comes down with a rash, they might go to the doctor and come away with some ointment to put on it. Indo-Pacific bottlenose dolphins get skin conditions, too, but they come about their medication by queuing up nose-to-tail to rub themselves against corals. In the journal iScience on 19 May, researchers show that these corals have medicinal properties, suggesting that the dolphins are using the marine invertebrates to medicate skin conditions.
Thirteen years ago, co-lead author Angela Ziltener a wildlife biologist at the University of Zurich, first observed dolphins rubbing against coral in the Northern Red Sea, off the coast of Egypt. She and her team noticed that the dolphins were selective about which corals they rubbed against, and they wanted to understand why. “I hadn’t seen this coral rubbing behavior described before, and it was clear that the dolphins knew exactly which coral they wanted to use,” says Ziltener. “I thought, ‘There must be a reason.’”
She and her colleagues were able to identify and sample the corals that the dolphins were rubbing on. Ziltener and her team found that by repeatedly rubbing against the corals, Indo-Pacific bottlenose dolphins were agitating the tiny polyps that make up the coral community, and these invertebrates were releasing mucus. In order to understand what properties the mucus contained, the team collected samples of the coral.
When lead author Gertrud Morlock, an analytical chemist and food scientist at Justus Liebig University Giessen in Germany, and her team used planar separations combined with on-surface assays and high-resolution mass spectrometry to analyze samples of the gorgonian coral Rumphella aggregata, the leather coral Sarcophyton sp., and the sponge Ircinia sp., they found 17 active metabolites with antibacterial, antioxidative, hormonal, and toxic activities.
This discovery of these bioactive compounds led the team to believe that the mucus of the corals and sponges is serving to regulate the dolphin skin’s microbiome and treat infections. “Repeated rubbing allows the active metabolites to come into contact with the skin of the dolphins,” says Morlock. “These metabolites could help them achieve skin homeostasis and be useful for prophylaxis or auxiliary treatment against microbial infections.”