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Key points
- Manta rays are intelligent and social animals that gather in large numbers to feed on plankton and be cleaned by smaller cleaner fish.
- Observations collected at cleaning stations shows mantas move and position specialized fins called cephalic lobes toward other animals during social interactions.
- Scientists say the fin movements appear to be a form of gestural communication, like human sign language, and could be an important part of their social behavior.
- Learning about mantas' social behavior could help in the development of sustainable ecotourism and conservation initiatives.
New research documents manta rays moving their cephalic lobes—the modified fins on either side of their mouths—during social interactions with cleaner fish, one another, and human divers. The study, published in Behavioral Ecology and Sociobiology, suggests that cephalic lobe movements may play a role in gestural communication, as well as in feeding.
The cephalic lobes are a distinct feature of manta rays. They are a pair of flexible fins positioned on the side of the head specialized for directing water (and hence zooplankton) into the mouth. As maneuverable, hydrostatic organs, the cephalic lobes can move independently of each other and extend in various ways. Although specialized for feeding, the lobes may have a variety of uses.
Reef manta rays (Mobula alfredi) gather in large numbers around Raja Ampat, in the Indonesian province of West Papua, to feed on zooplankton and be cleaned by smaller fish. These gatherings are also an opportunity for social interaction. Previous work from this research team, which includes scientists from Marine Megafauna Foundation, Macquarie University, the University of Cape Town, and the University of Papua, showed that reef manta rays are incredibly social animals, with individuals recognizing and remembering their “friends” and forming social groups.
The mantas in Raja Ampat are used to the presence of human divers and can be curious, but mostly carry on with their natural cleaning and social behaviors, says senior author Culum Brown of Macquarie University.
“They will frequently approach to check you out and as they do so, they move their cephalic lobes,” he says. “It looked to us as though they were also using these fins as a kind of sign language to greet other animals.”
Different Types of Manta Ray Movement
From observations recorded at cleaning stations in Raja Ampat, Brown and his colleagues described various types of cephalic lobe movements and positions made by the mantas in different contexts.
Certain movements, such as small flicks of the lobe tips, were performed more frequently when rays were facing another individual, while tight rolling of the lobes was associated with being followed by others. Brown says they seemed to use specific lobe movements to greet other mantas and possibly get their attention.
Some lobe movement types were also made more frequently when interacting with cleaner fish. Most fish use specific gestures to solicit cleaning from cleaner fish, so this finding did not surprise Brown. He says the more surprising (and stranger) finding was that the mantas also gestured with their cephalic lobes when approaching human divers.
“They probably do this out of a sense of curiosity,” he says. “Perhaps they are trying to greet us? Who knows?”
Brown and his colleagues say that it seems clear the mantas are using their cephalic lobes to communicate; we just don’t have any idea what they are saying. It is also difficult to tease out which lobe movements are meant to communicate a message and which ones are made to streamline swimming or feed on zooplankton. To demonstrate that these movements really are a form of gestural communication, future research should investigate how other mantas and cleaner fish respond to the signals.
Why Manta Ray Research Matters for Conservation
“Our results add to the growing evidence that manta rays are fundamentally a social species, which is crucial knowledge for conservation,” says Robert Perryman, lead author of the study and a doctoral student at Macquarie University.
Although protected in Indonesia since 2014, manta rays still face threats including illegal fishing, ocean pollution, and climate change. But Perryman says an increasing problem may be people with good intentions who just want to see mantas in their natural habitat.
“We need to think carefully about how tourists could affect mantas’ natural behaviors, including social interactions,” he says. “Mantas are curious and approachable animals and extremely tolerant of humans, but we have seen them stop visiting particular sites if the pressure of tourism grows too much.”
Perryman says that at their field site in Raja Ampat, the team has been trialing restricting the number of boats and people in the water and promoting a code of conduct for interacting responsibly with manta rays. He hopes research like this also helps to broaden public support and enthusiasm for their protection around the world.
“Collecting information about manta rays’ social interactions, particularly at sites where they regularly encounter divers, is important to develop sustainable ecotourism and conservation initiatives that allow mantas to coexist with humans in their natural habitats,” Perryman says.
“We hope that showing the social nature of manta rays add to their overall perception by humans and demonstrates that they are fascinating and complex animals, deserving of our protection.”
References
Perryman, R.J., Carpenter, M., Lie, E., Sofronov, G., Marshall, A.D., and Brown, C. Reef manta ray cephalic lobe movements are modulated during social interactions. Behav Ecol Sociobiol 75, 51 (2021). Doi: 10.1007/s00265-021-02973-x.
