An image of a dolphin with her calf swimming near coral along the sea floor
When a group of 360 dolphins visited corals located in the Northern Red Sea, reseachers noticed that calves under one year old would watch adults brush themselves against the coral. Angela Ziltener

When wildlife biologist Angela Ziltener went on deep-sea dives, she often observed something extraordinary. A group of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) lined up and took  turns rubbing their bodies against corals or sea sponges along the seafloor. After observing the behavior for over a decade as an “adopted member of the pod, ” the  University of Zurich scientist  and her team found that the sea mammals may be using the invertebrates as pharmacies to self-medicate, reports Erin Garcia de Jesús for  Science News .   The study detailing the particular find was published this month in  iScience .

The dolphins brush up against soft gorgonian corals ( Rumphella aggregata ), sturdier leather corals ( Sarcophyton   sp. ) and other specific sponges ( Ircinia   sp. ). The  sea mammals  slide into the branches multiple times, and  push body parts like their heads or flukes against more compact corals and sponges,   Popular Science’s   Kate Baggaley reports.  

Some dolphins even rip out leather coral from the seabed, hold it in their mouths, and wave it around until a yellow and green substance oozes out and stains their own snouts and bodies. The  invertebrates may make antibacterial compounds that they release  into the water that give the dolphins  healthy skin, per  Science News . Overall, the gathering is peaceful, and dolphins won’t fight each other to rub against the coral reefs. “It’s not like they’re fighting each other for the turn, ” Ziltener says to  Science News . “No, they wait, and then they go through. ” Previous studies have found that dolphins are vulnerable to skin ailments like poxvirus infections or fungal diseases like lobomycosis, Science reports.

Researchers also observed adult dolphins teaching young calves the behavior. When a group of 360 dolphins visited corals located in the Northern Red Sea, they noticed that calves under one year old would watch adults brush themselves against the coral, reports  Well-known Science . Adult dolphins only rubbed against the invertebrates under quiet and calm conditions. If boats disturbed  the area, dolphins didn’t  engage in the behavior.

“This is very valuable work, ” Michael Huffman, an  expert on animal self-medication at Kyoto University  not involved with the research, tells Tess Joose for Science . “I’ve long awaited a really solid study of self-medication in a marine animal species. ” After analyzing the pieces of the dolphins’ preferred coral and sponges for massaging, researchers found 17 total compounds in the invertebrates, per  Science News . Ten of the compounds had antibacterial properties or antimicrobial activity. Other compounds resembled the estrogen hormone. Estrogen helps keep the skin firm plus moisturized in humans,   Popular Science   reports.

More research is needed to confirm if the dolphins are buffing against coral reefs and sponges to treat skin infections since experts have not observed or seen proof of a coral cure, Science Information reports. The team plans to look into how the coral rubbing behavior differs in dolphins of different sexes and ages—and which areas of the body dolphins brush the most. Ziltener tells  Popular Science   that while more studies are needed, the find reveals the importance of conserving coral reef systems. “So far in this publication, we just can show the link between the invertebrates and the dolphins, ” Zeiltener tells  Popular Science .

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