by They were selective about the type of coral they would rub, said wildlife biologist Angela Ziltener, a visiting researcher at the University of Zurich who spent the next 13 years trying to unravel the complex behavior.
The results of her extensive research in the 360 dolphin community were published on Thursday.
Observing dolphins and studying the properties of corals, Ziltener and her colleagues discovered that dolphins appear to use the reef as medicine: Bioactive compounds in mucus released by two different types of corals and a marine sponge probably helps dolphins protect their skin.
Building trust
Ziltener took years of diving with the local dolphin population to gain their trust. “You have to be somewhat adopted by the dolphins. It took time to really see all their secrets,” he said.
The dolphins were rubbed only with a mermaid coral known as Rumphella aggregata, the leather coral Sarcophyton sp. and the marine sponge Ircinia sp., Ziltener observed. In addition, they used the organizations in different ways.
With leather corals and sponges – which are more compact and harder in texture than soft coral branches – dolphins tended to push an isolated part of the body and twist it around, according to the study. Instead, they slid their whole body into the mermaid coral several times, rubbing many parts of their body at the same time.
The behavior of dolphins in rubbing the mermaid coral, called gorgoning, and Ziltener’s research were first revealed in 2017 in the BBC documentary “Blue Planet II” and many other nature documentaries. However, this is the first time a detailed study of behavior has been published in a scientific journal.
When in groups, dolphins were often lined up and rubbed alternately with mermaid coral. Interaction with leather coral did not seem to be a group activity.
With a leather coral, a dolphin sometimes uprooted it from the ground and carried it in its mouth for a few minutes, shaking it around – an action that caused the compounds to leak from the coral and spread around the dolphin’s head, soiling the yellow and green.
Coral specimens
Because the reef is protected, the team was allowed to take small samples – just one centimeter – corals and marine sponge used by dolphins. The study found that these organisms contained 17 bioactive compounds with different properties, such as antibacterial, antioxidant or hormonal properties, said co-author Gertrud Morlock, an analytical chemist and professor. food science at Justus Liebig Giessen University in Germany.
The three different organizations showed similar, and somewhat different, results, Morlock said.
“The common denominator was that all three had a variety of antibacterial and antimicrobial effects. And what was special about the skin fold, for example, was that it contained estrogen-like compounds, while the other two did not.”
“We were surprised to find that there were so many (associations),” he said. “We believe that (dolphins) choose these substrates very clearly and we have proven that they have bioactive compounds even when rubbed on it (coral), “Their skin is in direct contact with these molecules.”
Skin treatment
The purpose of the behavior is likely to regulate and protect the skin microbiome – a bit like how people can use a skin cream, Morlock explained. He said the research team had no conclusive evidence that dolphins used coral as a form of medicine, although dolphins regularly suffer from fungal infections and skin rashes.
Not every dolphin is rubbed on the pod with coral. Young calves under 1 year old are just watching, Ziltener said. This led the researchers to believe that behavior is learned rather than innate.
“This ability to remember behaviors and their consequences and then repeat those behaviors to treat future skin problems adds to the wealth of evidence that dolphins are smart,” he said.
Dolphins have long been regarded as highly intelligent animals that are able to communicate and use tools, such as shells, to help them hunt. Ziltener said it is possible for other marine animals to use coral in this way, but it is difficult to observe systematic underwater animals.
Ziltener said dolphins often wake up to do coral friction behavior.
“It’s almost like taking a shower, cleaning before going to bed or waking up for the day,” he said.
