Bottlenose dolphins may use corals to help treat skin infections

Dolphins need a bit of skincare from time to time, new international research suggests.

A paper published in the journal iScience has reported that Indo-Pacific bottlenose dolphins rub themselves against corals in reefs off the coast of Egypt. Co-lead author on the paper, Angela Ziltener of the University of Zurich in Switzerland, first observed this behaviour over a decade ago.

“I hadn’t seen this coral rubbing behaviour 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.’”

Two bottlenose dolphin adults and one calf at a coral reef
A bottlenose dolphin calf being taught how to rub against the coral by its mother. Credit: Angela Ziltener.

“Many people don’t realise that these coral reefs are bedrooms for the dolphins, and playgrounds as well,” Ziltener continues. According to her, the dolphins will often head over to the corals after waking up from a nap – much as a human might shower after getting out of bed. They will even form queues to wait their turn for a coral session.

After some time diving with the dolphins and letting them get used to her, Ziltener was able to zero in on exactly which corals the dolphins were using. She and her team then collected samples of the gorgonian coral species Rumphella aggregata and a leather coral species, as well as a sponge.

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As the dolphins rub against them, the microscopic polyps that make up the corals are agitated and release mucus. By analysing the chemistry of the coral samples, the researchers hoped to understand what the mucus might contain and how it would affect the dolphins.

The coral and sponge samples were analysed using high-resolution mass spectrometry and other techniques by a team at Justus Liebig University Giessen in Germany led by co-first author Gertrud Morlock. 

Dolphins “queuing” to rub against gorgonian corals. Credit: Angela Ziltener.

Morlock’s team found several bioactive compounds in the corals, including 17 with antibacterial, antioxidative, hormonal and toxic properties. The researchers now believe these properties could be helping protect against or treat skin infections in the dolphins.

“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.”

Read more: Female dolphins like to get frisky

Ziltener hopes to continue studying how the dolphins use corals. She is also the president of Dolphin Watch Alliance, a conservation organisation that aims to promote tourism experiences that are safe for dolphins.

“The tourism industry makes a lot of money now out of dolphin swimming,” Ziltener explains. “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.”

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