Dolphins do skin care with corals

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Mother dolphin with her calf at the “medicinal” corals. © Angela Ziltener

In the Red Sea off the coast of Egypt, a wildlife biologist has observed dolphins behaving astonishingly: they regularly rub against certain corals – and even queue up behind their fellow dolphins until it is their turn. But why? To answer this question, the researchers took samples of the corals and sponges preferred by the dolphins and examined them in the laboratory. The result: The friction releases bioactive substances with antibacterial properties. It is possible that the dolphins use the coral reefs as a kind of pharmacy to prevent and treat skin diseases.

Numerous animal species are known to seek their own remedies in the wild: chimpanzees eat medicinal plants when they have intestinal problems, honey bees produce and use the antibacterial substance propolis, and some birds make their nests from plant materials that prevent mite infestation in their offspring. Behavior has also been observed in dolphins that suggests self-medication: Bottlenose dolphins regularly rub against certain corals. To what extent these have medicinal properties, however, was previously unclear.

Pharmacy in Coral Reef

A team led by Gertrud Morlock from the University of Gießen has now analyzed two types of corals and a sponge that dolphins prefer to visit: the gorgonian coral (Rumphella aggregata), the leather coral (Sarcophyton sp.) and the sea sponge Ircinia. In fact, they identified 17 active metabolites with antibacterial, antioxidant, hormonal and toxic effects. “Repeated rubbing causes the active metabolites to come into contact with the dolphin’s skin,” explains Morlock. “The metabolites could help stabilize skin homeostasis and be useful for prophylaxis or adjunctive treatment against microbial infections.”

The research team concludes that the dolphins are in fact practicing a form of self-medication. Co-author Angela Ziltener had already suspected this in 2009, when she observed for the first time during research dives in the Red Sea off the coast of Egypt how bottlenose dolphins rubbed against corals and even “queued” until it was their turn. “I had never seen this behavior before, and it was clear that the dolphins knew exactly which coral they wanted to use,” says Ziltener.

learned behavior

To find out exactly which corals the bottlenose dolphins chose, the research team first had to gain the animals’ trust. It was only when the dolphins allowed the researchers to get closer that they were able to identify and sample the corresponding corals and sponges. They also found that the intensive rubbing releases a slime from the corals, which probably sticks to the dolphins’ skin.

During the behavioral observations, the researchers also noticed that the dolphin calves did not participate in the rubbing procedures, but watched the older group members doing it. When they first participated, around the age of one year, they approached the coral cautiously at first and only touched it with parts of their bodies. Only gradually did they learn to rub against it from nose to tail. “This could mean that the behavior and the potential knowledge about the effects of the contained bioactive substances are not innate but acquired through social learning processes,” the authors write.

Source: Gertrud Morlock (University of Gießen) et al., iScience, doi: 10.1016/j.isci.2022.104271

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