What do we know about the evil that is killing the dolphins?
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(CNN) --
In the Red Sea off the coast of Egypt, bottlenose dolphins were seen doing something unusual in 2009.
They lined up to rub their bodies against the coral.
They chose what kinds of corals they rubbed against, noted wildlife biologist Angela Ziltener, a visiting researcher at the University of Zurich who spent the next 13 years trying to unravel the puzzling behavior.
The results of their extensive research on the community of 360 dolphins were published this Thursday.
In the dolphin watching and studying the properties of the coral, Ziltener and his colleagues discovered that dolphins seem to use the reef as a kit: the bioactive compounds in the mucus released by two different types of coral and marine sponge probably help dolphins protect your skin.
It is the first time such behavior has been observed in cetaceans — the scientific order of marine mammals that includes dolphins, whales and porpoises — according to the study.
However, it has previously been observed that some birds, mammals, insects, and reptiles use plant parts or other substances to combat pathogens or parasites.
building trust
It took Ziltener years of diving with the local dolphin population to gain their trust.
"You have to be adopted by the dolphins. He took time to see all the secrets of him," he said.
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The dolphins only rubbed against a gorgonian coral known as Rumphella aggregata, the leather coral Sarcophyton sp.
and the sea sponge Ircinia sp., Ziltener observed.
In addition, they used the organisms in different ways.
With leather corals and sponges, which are more compact and harder in texture than the soft branches of gorgonian coral, the dolphins tended to push on an isolated body part and twist it, according to the study.
Rather, they slid their entire bodies into the gorgonian coral multiple times, rubbing various body parts at once.
The dolphins' behavior of rubbing against gorgonian coral, called gorgoning, and Ziltener's research were first revealed in 2017 in the BBC documentary "Blue Planet II" and other nature documentaries.
However, this is the first time that a detailed study of the behavior has been published in a scientific journal.
When in groups, the dolphins would often line up and take turns rubbing up against the gorgonian coral.
Interacting with the leather coral did not appear to be a group activity.
With leather coral, a dolphin would sometimes pluck it off the ground and carry it in its mouth for a few minutes, rocking it, an action that caused the compounds to come out of the coral and spread around the dolphin's head, turning it yellow and green. .
coral samples
Because the reef is protected, the team got permission to take small samples—just one centimeter—of the corals and sea sponges used by the dolphins.
Analysis of the study found that these organisms contained 17 bioactive compounds, with different properties, such as antibacterial, antioxidant or hormonal attributes, said co-author Gertrud Morlock, an analytical chemist and professor of food sciences at Justus Liebig University Giessen in Germany.
The three different organisms showed similar and some different effects, Morlock said.
"They had in common that all three had a lot of antibacterial and antimicrobial activities. And what was special to the leather pen, for example, contained estrogen-like compounds, while the other two did not."
Dolphins learn the behavior to protect their skin instead of being innate.
"We were surprised to find that there were so many (compounds)," he said.
"We think that (the dolphins) very clearly select these substrates, and we have proven that they have bioactive compounds and when they rub on this (the coral), their skin is in direct contact with these molecules."
skin treatment
The purpose of the behavior is likely to be to regulate and protect the skin's microbiome, a bit like humans might use a skin cream, Morlock explained.
She said the research team had no definitive proof that the dolphins were using the coral as a form of medicine, although dolphins regularly suffer from fungal infections and skin rashes.
Not all of the dolphins in the pod rub against the coral.
Calves under 1 year old just watch, Ziltener said.
This led researchers to believe that behavior is learned rather than innate.
"Initially, this behavior could have arisen as a result of impulse or instinct, or simply by chance. Perhaps, a dolphin with irritated skin rubbed a random coral that released skin-healing chemicals. The relieved dolphin recalled the behaviors and repeated, then taught those behaviors to others, as in the case of the Australian population using bottlenose sponges," said Diana Barrett, a professor in the department of biology at the University of Massachusetts Dartmouth, who was not involved in the research.
"This ability to remember behaviors and their resulting effects, and then repeat those behaviors to treat future skin problems, adds (to) the wealth of evidence that dolphins are intelligent," he said.
Dolphins have long been seen as highly intelligent animals that can communicate and use tools, such as shells, to help them hunt.
Ziltener said it's possible that other marine animals could use corals in this way, but it's difficult to systematically observe underwater animals.
Ziltener said that dolphins often wake up from their nap to perform coral-rubbing behavior.
"It's almost like they're taking a shower, cleaning up before going to sleep or getting up to start the day," he said.
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