Researchers have observed a unique behaviour among the bottlenose dolphins that inhabit the northern Red Sea, off the coast of Egypt: The animals rub their bodies against certain coral species, which the biologists believe is for medicinal purposes.
This process — zoopharmacognosy, or self-medication by non-human animals — has never been reported in cetaceans before, though other species have exhibited similar rubbing behaviours. In a recent paper, a team of chemists and biologists scrutinised the Red Sea’s Indo-Pacific bottlenose dolphin (Tursiops aduncus) population and their propensity for this rubbing behaviour.
The team also detailed the chemistry of the involved corals and the specifics of how the dolphins would interact with them. Their work is published today in iScience.
“Dolphins appear to be selectively matching certain body parts to specific corals,” said Angela Ziltener, a wildlife biologist at the University of Zurich, in an email to Gizmodo. “They seem to be very aware of what they are choosing. 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.”
Ziltener’s team observed the dolphins in the Red Sea numerous times and filmed the animals rubbing themselves on the coral. Ziltener said it appeared the dolphins were intentional about which corals they rubbed on and when. The animals rubbed their whole bodies on gorgonian coral (Rumphella aggregata), but mostly used leather corals and sponges on their heads, bellies, and tail fins. The dolphins avoided those coral, however, if they were growing close to potentially irritating species like fire coral, which are venomous.
The team suspects that the dolphins are benefitting from chemicals that the corals release to protect themselves from microbial infections. By rubbing their skin on the corals, the dolphins forced the coral polyps to release mucus — mucus that the researchers sampled and examined in the lab. Using mass spectrometry, they found that the mucus contained bioactive compounds, some of which had antibacterial properties.
“Repeated rubbing allows the active metabolites to come into contact with the skin of the dolphins,” said Gertrud Morlock, an analytical chemist at Justus Liebig University Giessen in Germany, and a co-author of the paper, in a Cell release. “These metabolites could help them achieve skin homeostasis and be useful for prophylaxis or auxiliary treatment against microbial infections.”
The researchers even observed the dolphins waiting in an underwater queue for their turn swimming through some of the coral. So not only do the animals stay healthy, but they remain polite all the while.
Because the region of the Red Sea the dolphins swim in is heavily trafficked by tourists, the researchers set up the Dolphin Watch Alliance to spread awareness of the creatures’ presence and the need to protect them. During some of the COVID-19 pandemic, a downturn in tourist traffic meant that the researchers were able to study the mammals in greater detail.
There’s still more to understand about the nature of the relationship between the dolphins and the coral. While it appears the mammals use the invertebrates for medicinal purposes, the researchers aren’t sure how not having the coral at all would affect the animals’ health. Future observations will likely reveal more about exactly what the dolphins get out of this routine rubbing.