Dolphins head to coral 'clinics' to treat skin infections

In the Northern sea, off the coast of Egypt, dolphins wait in line for their medication.

Their clinics? Corals.

Indo-Pacific bottlenose dolphins have been found queuing up nose-to-tail to rub themselves against corals, which heals them of their skin problems. 

A report in iScience has revealed that these corals have medicinal properties, suggesting that the dolphins are using the marine invertebrates to medicate skin conditions. 

Fascinating, isn't it.

The phenomenon was first spotted 13 years ago.

Where it all began

Co-lead author Angela Ziltener, a wildlife biologist at the University of Zurich, Switzerland, first observed dolphins rubbing against coral in the Egyptian Northern Red Sea. Her team immediately noticed that the dolphins were selective about the corals they rubbed against. That kind of intuition demanded an answer.

“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.'"

Now, most dolphin research is conducted from the surface of the water. But Ziltener was a diver, and it gave her the advantage to explore dolphins up close.

It did take some time to earn the trust of the pod, which she was able to do also because these dolphins weren't fazed by the large bubbles released by the diving tanks and habituated towards divers.

“Some dolphins, like spinner dolphins in the Southern Egyptian Red Sea, are shyer regarding bubbles,” she says.

Once the pod allowed her to visit them regularly, Ziltener and her colleagues were able to identify and sample the corals that the dolphins were rubbing on. She 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.

Solid protection against microbial infections

It was imperative to understand the properties of this mucus, and so the team collected samples of the coral.

Enter lead author Gertrud Morlock, an analytical chemist and food scientist at Justus Liebig University Giessen in Germany. She 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.

Their findings revealed the presence of 17 active metabolites with antibacterial, antioxidative, hormonal, and toxic activities.

The 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.”

The dolphins need a safe space too

These reefs also serve as bedrooms and playgrounds for the local dolphin populations.

In between naps, the dolphins often wake to perform the coral rubbing behavior. “It’s almost like they are showering, cleaning themselves before they go to sleep or get up for the day,” Ziltener says.

Ever since she began researching dolphins in Egypt in 2009, Ziltener has noticed an alarming trend. 

“The tourism industry makes a lot of money now out of dolphin swimming. People are dreaming of swimming with the dolphins, so they are figuring out which reefs they use and disturbing the dolphins if they don’t follow the guidelines for how to approach them in a responsible way,” she says.

She was so worried that she started a conservation group called Dolphin Watch Alliance that educates and informs tour guides, tourists, and the public on how to give tourists experiences that are safe for dolphins. The group also lobbies for the reefs to become protected areas.

As long as the reefs remain a safe place for the dolphins, Ziltener and her team can continue to study coral rubbing and identify which selected corals are being used for specific body parts.