Dolphins think of corals as sort of the medicine cabinet of the ocean.
Just like humans turn to ointment to medicate a rash, some dolphins rub themselves against specific corals to soothe skin conditions, a new study finds.
Researchers studied Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Northern Red Sea in Egypt. They noticed that they lined up to rub certain body parts against certain corals and sponges.
Scientists found these specific marine invertebrates have medicinal capabilities, which suggests the dolphins use them to self-medicate skin conditions.
Co-lead author Angela Ziltener, a wildlife biologist at the University of Zurich, Switzerland, tells Treehugger she is interested in how intelligent behavior differs from species to species, particularly in intelligent species close to humans.
“Bottlenose dolphins have highly developed cognitive skills such as self-recognition, tool using (for example foraging with a sponge in Shark Bay), learning from each other and transferring the knowledge to the next generation (culture),” Ziltener says.
“They also have a long-life history and a fission and fusion society like humans and a highly developed communication system.”
In 2004, when Ziltener first went diving in the Northern Red Sea, Egypt, she witnessed wild Indo-Pacific bottlenose dolphins rub against gorgonian coral. She and her team noticed the dolphins were picky about which coral they rubbed against and were curious why they were so choosy and why they did it in the first place.
Because Ziltener is a diver, she says she was accepted into the dolphin group and was able to study them up close.
“On the gorgonian coral, dolphins slide into the branches of the coral and rub several body parts against it. Upon rubbing, the gorgonian coral polyps start to secrete mucus and to close and the mucus secreted by the corals can then be transferred to the skin of the dolphin,” Ziltener explains.
“Through the closed polyps and resultant harder and rougher surface of the coral, skin contact via abrasion and subsequent absorption might be even more efficient. For example, the dolphin rubs its ventral, lateral, or dorsal body part on the leather coral and its head and fluke [tail fin] often touches the coral, too.”
Sometimes, researchers observed a dolphin rub its belly or back and tail fin on a sponge, push its head strongly against it, and then twist around.
Researchers studied the dolphins as they rubbed against gorgonian coral (Rumphella aggregata), leather coral (Sarcophyton sp.), and a sponge (Ircinia sp.).
“Dolphins queue up behind each other and wait for their turn to approach the invertebrate,” Ziltener says. “This group event has been observed for the gorgonian coral and sponge, but not for the leather coral. The leather coral rubbing appears more randomly, mostly alone.”
Mucus and the Microbiome
Lead author Gertrud Morlock, an analytical chemist and professor at Justus Liebig University Giessen in Germany, analyzed samples of the corals and sponges along with her team. They found 17 active metabolites with antibacterial, antioxidative, hormonal, and neurotoxic activities.
Discovering these bioactive compounds in the corals and sponges led the researchers to believe that the mucus in the invertebrates helps regulate the microbiome in the dolphin’s skins and treats infections.
“Leather corals and sponges are more compact and harder in their texture than the soft gorgonian coral branches, so the dolphins push one particular body part strongly into the selected substrate,” Ziltener says. “Repeated rubbing allows the active metabolites to come into contact with the skin of the dolphins, which in turn could help them achieve skin homeostasis and be useful for prophylaxis or auxiliary treatment against microbial infections.”
The results were published in the journal iScience.
Coral Reefs for Rest and Fun
Coral reefs act as both bedrooms and playgrounds for dolphins, Ziltener says. They go there to rest and to have fun.
“The reefs give them shelter and protection from predators like sharks,” she says. “They are hunting in the deeper water in the night and coming to the reefs during daytime to rest, socialize, and clean their skin.”
She says it’s almost as if they are cleaning off before they go to sleep at night or get up to start the day.
“Because the dolphins chose particular corals or sponges to rub specific body parts,” Ziltener says. “The more sensitive calves aged under one year have not been observed engaging in the group rubbing on these particular organisms, instead they watch the adults doing the rubbing. We know that dolphins learn from each other and transfer the knowledge to the next generation (culture).”
Ziltener and her team started an organization called Dolphin Watch Alliance, a nonprofit group focused on research, awareness, and conservation of wild dolphins. One focus is on protecting the animals from human threats such as unregulated dolphin tourism.
She says, “The aim is respectful and regulated encounters between humans and animals in the wild, taking into account the needs of all parties.”