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Dolphins heal their skin by exercising on certain corals and sponges.

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Just like we use medicines to treat skin problems, animals find medicines in nature. For example, wild Indo-Pacific bottlenose dolphins have been observed in their natural environment rubbing against selected corals and sponges in the northern Red Sea in Egypt. Researchers have shown that these marine invertebrates have medicinal properties against dolphin skin problems because they contain biologically active metabolites. Repeated rubbing allows these active metabolites to come into contact with the skin of dolphins, which may also be useful against microbial infections, as a preventive measure or treatment.

“I have never seen this kind of coral-rubbing behavior described before, and it is clear that dolphins know exactly what kind of coral they want to use,” Angela Ziltener, a wildlife biologist at the University of Zurich, explained in a press release. (Switzerland). and co-author of the study. “I thought there must be a reason.” The researcher and her team had already observed this behavior thirteen years ago, but it took them a while to study it closely and gain the trust of the dolphins.

Selective use of corals and sponges

In nature, friction against various substrates is part of the classic physical contact behavior in cetaceans, but so far it has only been observed in killer whales and beluga whales. The bottlenose dolphins studied constantly encounter three different marine invertebrates: gorgons (Rumphella aggregata), leatherbacks (Sarcophyton sp.) and sponges (Ircinia sp.). Each invertebrate is used selectively for a particular body part, as the texture of each substrate is unique.

In the past, similar gorgonian species were known to produce antimicrobial and cytotoxic secondary metabolites, and leather corals and sponges contain bioactive metabolites. That’s why the researchers in the new study relied on the hypothesis that these invertebrates self-medicate against skin disease pathogens.

Since 2009, about 360 Indo-Pacific bottlenose dolphins in the northern Red Sea have been surveyed by the research team using a unique combination of boat surveys and scuba diving. Ziltener and his team found that when Indo-Pacific bottlenose dolphins hit invertebrates, they waved tiny polyps and the substrate secreted mucus. In addition, in groups, dolphins have been observed to “stand in line” to get to the natural cure.

“On gorgons, dolphins slip into coral branches and often repeat this behavior so that several parts of the body rub,” the study authors write. “When rubbed, the gorgonian polyps begin to secrete mucus and close, and the mucus secreted by the corals can then be transferred to the skin of the dolphin. Leather corals and sponges are denser and harder in texture than the soft branches of gorgonians, so dolphins embed the isolated part of their body deeply into the substrate.” For example, a dolphin rubs its ventral, lateral, or dorsal body against leather coral.

Dolphin rubbing behavior (A) gorgonian Rumphella aggregata, (B) leatherback coral (Sarcophyton sp.), and (C) sponge Ircinia sp. ; (D) Underwater photographic documentation of sampling and their locations, eg for leatherback coral. © Morlock, Ziltener, Geyer et al. (2022)

17 active metabolites against skin diseases and microbial infections

To understand the properties of the slime, the researchers took coral samples and found 17 active metabolites with antibacterial, antioxidant, hormonal, and toxic activities. “These metabolites may help them achieve skin homeostasis and be useful for prevention. [la prévention] or an adjuvant treatment against microbial infections,” says co-author Gertrud Morlock, an analytical chemist and food scientist at the Justus Liebig University in Giessen, Germany. To gather information about the activity of the compounds and identify them, the scientists relied on separation science and high-resolution mass spectrometry on a single absorbent surface.

Although the study provides evidence for the use of invertebrates in dolphin self-medication, the volume of invertebrate specimens remains limited. In addition, she calls for further research into the interactions between vertebrates and invertebrates in coral reefs and the importance of efforts to conserve this important marine life habitat. Indeed, the tourism industry (such as swimming with dolphins) can disrupt the habits of dolphins in their natural state.

iScience

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