Hitchhiking fish called remoras are known for sticking to bigger marine animals for rides. However, a new study reveals a surprising twist: these fish sometimes squeeze into the rear ends of manta rays.
Remoras, part of the Echeneidae family, often attach themselves to sharks, whales, and turtles using their unique suction discs. Previously, scientists believed this partnership was beneficial for both parties, with remoras providing a cleaning service. But this recent research suggests that might not always be the case for manta rays.
Emily Yeager, a marine biology doctoral candidate at the University of Miami, explained how a diver watched a remora slide into a manta ray’s cloacal opening. The ray didn’t seem comfortable with the intrusion, shaking after the remora’s sudden movement. This behavior, detailed in a recent study in Ecology and Evolution, challenges the assumption that remora-host relationships are harmless.
Yeager noted that remoras often appear to travel alongside their hosts without causing visible harm. However, this new evidence indicates that mantas might struggle to remove remoras from their bodies. “The manta’s ability to dislodge the remora is probably quite limited,” Yeager commented.
David Shiffman, a marine conservation biologist, expressed both amazement and concern. He pointed out that while the remoras might benefit, it may be discomforting or even damaging for the manta rays.
In expanding on this behavior, Yeager gathered reports from manta ray experts worldwide. She found cloacal diving—where remoras enter the cloaca—has been observed only seven times over 15 years, hinting that this might be more common than thought, but easily overlooked.
Historically, symbiotic relationships have been categorized into mutualism (both benefit), commensalism (one benefits, no harm to the other), and parasitism (one benefits at the other’s expense). Yeager suggests this interaction might fit better in the parasitism category due to potential harm to the manta rays, raising questions about our understanding of these interactions in ocean ecosystems.
The study also discusses the broader implications of these findings. Manta rays might face discomfort, energy loss from trying to rid themselves of remoras, or even challenges during reproduction. Observations show mantas engaging in behaviors like jumping out of water or rubbing against surfaces to try to remove the fish.
Yeager emphasizes that relationships in nature can be complex and varied rather than easily placed in boxes. She compares this to family dynamics: while some days might be good, others can be challenging. By spending more time observing these interactions, we can gain deeper insights into the underwater world.
For more detailed information, the full study can be accessed here.
