Dolphins use healing properties of corals, study suggests

In the Red Sea off the coast of Egypt, dolphins were seen in 2009 doing something unusual. They lined up to rub their bodies against the corals.

They were picky about what kind of corals they rubbed, noted wildlife biologist Angela Ziltener, a visiting researcher at the University of Zurich who spent the next 13 years trying to unravel the baffling behavior.

The results of its extensive survey of the community of 360 dolphins were published this Thursday (19).

By observing dolphins and studying the properties of coral, Ziltener and his colleagues found that dolphins seem to use the reef as a medicine chest: bioactive compounds in mucus released by two different types of corals and a sea sponge likely help dolphins to protect your skin.

This is the first time this type of behavior has been witnessed in cetaceans — the scientific order of marine mammals that includes dolphins, whales and porpoises — the study said.

However, some birds, mammals, insects and reptiles have been observed using plant parts or other substances to fight pathogens or parasites.

building trust

Ziltener took years of diving with the local dolphin population to earn their trust. “You have to be kind of adopted by the dolphins. It took time to really see all the secrets,” she said.

The dolphins just rubbed against a gorgonian coral known as Rumphella aggregata, leatherback coral Sarcophyton sp., and sea sponge Ircinia sp., noted Ziltener. Also, they used the organisms in different ways.

With leathery corals and sponges — which are more compact and harder in texture than the soft twigs of gorgonian coral — dolphins tended to push an isolated body part and twist it, the study found.

In contrast, they slid their entire bodies onto the gorgonian coral several times, rubbing multiple body parts at once.

The dolphins’ behavior of rubbing against the gorgonian coral, and Ziltener’s research, were first revealed in the 2017 BBC documentary “Blue Planet II” and several other nature documentaries. However, this is the first time that a detailed study of the behavior has been published in a scientific journal.

When in groups, the dolphins often lined up and took turns rubbing against the gorgonian coral. Interacting with the leather coral didn’t seem like a group activity.

With leather coral, a dolphin would sometimes pull it off the ground and hold it in its mouth for a few minutes, shaking it — an action that caused the compounds to leak out of the coral and spread around the dolphin’s head, staining it. the yellow and green.

coral samples

As the reef is protected, the team obtained permission to collect small samples – just one centimeter – of the corals and sea sponges used by dolphins.

Analysis of the study found that these organisms contained 17 bioactive compounds, with different properties, such as antibacterial, antioxidant or hormonal attributes, said co-author Gertrud Morlock, an analytical chemist and professor of food science at Justus Liebig Giessen University in Germany.

The three different organisms showed similar and some different effects, Morlock said.

“In common was that all three had a wealth of antibacterial and antimicrobial activities. And what was special about the leather corral, for example, contained estrogen-like compounds, while the other two did not.”

“We were surprised to find that there were so many (compounds),” she said. “We think that (dolphins) select these substrates very clearly, and we’ve proven that they have bioactive compounds, and when they rub that (coral) their skin is in direct contact with these molecules.”

Skin treatment

The purpose of the behavior is to regulate and protect the skin’s microbiome — a bit like humans might use a skin cream, Morlock explained.

She said the research team had no definitive evidence that dolphins were using coral as a form of medicine, although dolphins regularly suffer from fungal infections and skin rashes.

Not all pod dolphins rub against corals. Puppies under a year old just watch, Ziltener said. This has led researchers to believe that behavior is learned rather than innate.

“Initially, this behavior may have come about as a result of impulse or instinct, or just by chance. Perhaps, a dolphin with irritated skin rubbed along a random coral that released skin-healing chemicals. The relieved dolphin remembered the behaviors and repeated them, then taught those behaviors to others, as in the case of the Australian population using bottle nose sponges,” said Diana Barrett, a professor in the biology department at the University of Massachusetts Dartmouth. , who was not involved in the research.

“This ability to remember behaviors and their resulting effects and then repeat those behaviors to treat future skin problems adds (to the) wealth of evidence that dolphins are intelligent,” she said.

Dolphins have long been seen as highly intelligent animals that are able to communicate and use tools, such as shells, to help them hunt.

Ziltener said it’s possible that other marine animals use corals in this way, but it’s difficult to observe underwater animals systemically.

She pointed out that dolphins often wake up from naps to perform the behavior of rubbing corals. “It’s almost like they’re showering, cleaning up before going to sleep or getting up for the day,” she said.