Dolphins use coral as medicine – and wait their turn to do so

This is the first time this behavior has been seen in cetaceans. The researchers collaborated with experts from the non-profit organization Dolphin Watch Alliance, who have been diving in the northern Red Sea since 2009 to build trust with schools of dolphins. “It takes time to understand the social structure and behavior of a dolphin population,” said Gertrud Morlock, lead author of the study.

The behavior turned out to be complex: the dolphins selected only a few corals to rub against, and did so with specific, presumably affected body parts. If a coral was already busy, the animals waited patiently for their turn. In addition, the researchers saw that young dolphins watch from a distance before they themselves carefully swim along the coral – an indication that the behavior is not innate, but learned.

To determine whether the sanding was really intended as self-medication, the scientists took small samples of the corals to a lab to analyze their chemical composition. The researchers found no fewer than seventeen ingredients with a medicinal effect, from antibacterial substances to antioxidants. This made self-medication a “pretty plausible” explanation, according to Morlock.

polyps

Incidentally, the fabrics do not come from the corals themselves, but from small polyps that live in the corals. When a dolphin rubs against a coral, the polyps secrete mucus that deposits on the dolphin’s affected skin. In some cases, the researchers even saw some dolphins pull pieces of coral from the bottom and shake them to get the slime out of the coral.

This is a remarkable study for several reasons, says Fleur Visser, whale ecologist at the University of Amsterdam, who was not involved in the study. Studies in which dolphins are followed for a long time are not uncommon, which, according to Visser, makes it extra special that this behavior has only now been discovered. Visser also calls the fact that substances from the corals have been chemically analyzed exceptional.

Yet, according to Visser, the analysis is not yet complete: ‘I would have liked the researchers to have also examined the surrounding corals, which the dolphins did not rub against,’ she says. It is possible that the unused corals also contain medicinal substances. In that case, self-medication is not the only possible explanation for the fastidiousness of the dolphins. “I expect they’ll look into that.”