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For manta rays, parasitic hitchhikers can be a pain in the rear, study finds

Giant remoras hitching a ride with an oceanic manta ray. Image by Guy Stevens / Manta Trust.

  • A new study has found that 13 species closely associate with reef manta rays and oceanic manta rays in the Maldives.
  • The associations between the manta rays and these other species are not always mutually beneficial, with the “hitchhiking” species usually gaining more benefits than they give to the manta rays.
  • The study is based on more than 76,5000 sightings of the two manta ray species over a 30-year period.

Manta rays tend not to swim alone. Not only do they socialize with their own kind, but they’re also accompanied by a range of different species — from sharksuckers to trevally to trumpetfish.

In a new paper published in PLOS ONE, a team of researchers from the Manta Trust, a U.K.-based charity, and the University of Bristol analyzed more than 76,500 sightings of reef manta rays (Mobula alfredi) and oceanic manta rays (Mobula birostris) over a 30-year period in the Maldives to figure out what kinds of species associated with them. The most common “hitchhiker” species seen with these rays were sharksucker remoras (Echeneis naucrates) and giant remoras (Remora remora), which are both from the Echeneidae family. But the researchers also identified 11 other tag-along species, including the black trevally (Caranx lugubris), rainbow runner (Elagatis bipinnulata), and Chinese trumpetfish (Aulostomus chinensis).

The study identified thirteen different species associated with manta rays in the Maldives. Image courtesy of the

“There have been a few studies [focusing on] manta rays [and] remora species,” lead author Aimee Nicholson-Jack, a scientist at the Manta Trust, told Mongabay in an interview. “But our paper is the first to cover new hitchhiking species that aren’t part of the remora family.”

It’s generally been understood that manta rays have a symbiotic relationship with remora species: remoras will remove ectoparasites from their manta ray hosts, while the manta rays help remoras gain better access to food and shelter. But the researchers noticed that the remoras could also be somewhat parasitic to the manta rays.

“Mantas start to end up with quite severe red abrasions and open wounds from the remora literally clinging on to it just so constantly,” senior author Guy Stevens, chief executive and founder of the Manta Trust, told Mongabay. “And sometimes the remoras go inside the anus … of the manta, so you can have like a 3-foot [90-centimeter] remora literally swimming up your bum — that, I’m sure, can’t be that comfortable.”

An oceanic manta ray with an injury caused by a remora. Image by Guy Stevens / Manta Trust.

Other remora species will go into the manta rays’ mouths, spiracles or gill slits, causing injuries in the process, Stevens said.

Non-Echeneidae species, on the other hand, had a different kind of relationship with the manta rays. While these hitchhiker species gained some benefits, the manta rays received neither negative nor positive impacts from their presence, the study found.

The researchers also found that the remora species didn’t always stay with mantas for long periods of time.

“We always assumed that these remoras — these sharksucker remoras — were staying with their hosts on a long-term basis,” Stevens said. “But actually, I think what we’re starting to find now is that they may only be staying with them for one or two hours at a time, and then they’re free swimming or switching to other hosts.”

The relationships between manta rays and associated species could be influenced by season, location, and whether the manta rays were pregnant, the study found.

Golden trevalley swimming alongside a reef manta ray. Image by Guy Stevens / Manta Trust

Stephanie Venables, a senior scientist at the Marine Megafauna Foundation, said this study advances our understanding of manta rays and the fish that associate with them, which hasn’t been looked at in great detail thus far. But she also said that the findings weren’t entirely surprising.

“As someone who spends quite a bit of time in the water observing manta rays, the findings were somewhat expected in terms of the identified hitchhiker species and the differences observed between manta ray species and life stages,” Venables told Mongabay in an email. “There were a couple of hitchhiker species that I personally haven’t seen associating with manta rays in other parts of the world (Mozambique, Australia, Indonesia), which would make for an interesting comparison across different regions.”

Reef manta rays are considered to be vulnerable to extinction, while giant manta rays are endangered, mainly due to the fact that both species are directly targeted by fishers or accidentally caught as bycatch. Stevens said he hopes this new study can help protect these species by adding to our knowledge and understanding of them.

“If you want to protect a species like a manta ray, you need to understand how it interacts with other species in its environment,” he said. “We talk about these relationships being symbiotic, you know, mutually beneficial, in some cases, potentially parasitic in other cases. And obviously, as species interact in a beneficial or negative way with other species in their environment — that has potential life survival outcomes and species population survival outcomes.”

Citation:

Nicholson-Jack, A. E., Harris, J. L., Ballard, K., Turner, K. M., & Stevens, G. M. (2021). A hitchhiker guide to manta rays: Patterns of association between Mobula alfredi, M. birostris, their symbionts, and other fishes in the Maldives. PLOS ONE, 16(7). doi:10.1371/journal.pone.0253704

Banner image credit: Giant remoras hitching a ride with an oceanic manta ray. Image by Guy Stevens / Manta Trust.

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