Remoras are known for being the ocean’s hitchhikers because they spend most of their lives physically attached to hosts like whales, sharks and large fish. But these fish aren’t just mooching rides from their chauffeurs—the pair shares a mutually beneficial relationship. Hosts have potentially dangerous parasites removed while remoras get free meals, protection from predators and higher chances of meeting mates.
Scientists have long marveled at suckerfishes’ ability to stick to their hosts via a powerful suction disk on their heads, though they knew little about how it worked. Now, an accidental discovery has revealed the secret behind how remoras catch a ride.
Stanford marine biologist Jeremy Zucker had set out to learn about the feeding habits of blue whales in 2014 by attaching video cameras to their backs, reports Cara Giaimo for the New York Times. While reviewing the footage, he was surprised to see remoras skittering across the whales’ backs. “We were not expecting that at all,” Zucker told Giaimo.
It turns out that Zucker and his team had captured the first continuous recording of remora behavior on a host organism. An international team of scientists analyzed the footage and recently published their findings in the Journal of Experimental Biology. Previously, researchers only had still images and anecdotal evidence available to study remoras, according to a press release.
They discovered that remoras chose to stick to whales primarily at three places where they would face the least amount of resistance from the flow of water: behind the whale’s blowhole, behind and next to the dorsal fin, and above and behind the pectoral fin. There, remoras experienced up to 84 percent less drag, allowing them to cling to their hosts more easily.
Remoras aren’t necessarily hanging on for dear life. In fact, the suckerfish could freely move around on the whale, feeding and socializing even when their ride raced through the ocean at five meters per second. They did this by skimming and surfing within a thin layer of fluid just a few centimeters thick along the whale’s skin called a “boundary layer” that has lower drag forces compared to the flow outside the layer, a newly discovered behavior.
"Through lucky coincidence, our recordings captured how remoras interact in [whales’ flow] environment and are able to use the distinct flow dynamics of these whales to their advantage,” study co-author and assistant professor of biology at New Jersey Institute of Technology Brooke Flammang says in the press release. “It is incredible because we've really known next to nothing about how remoras behave on their hosts in the wild over any prolonged period of time."
Flammang and the other researchers analyzed live remoras and created a 3-D digital model of a blue whale. They wanted to run simulations of fluid flow on the model to determine how the remoras navigated their hosts, but because their computers were not powerful enough, the team had to turn to the Barcelona Supercomputing Center in Spain, per Amanda Buckiewicz of CBC Radio. In the process, the study produced the highest-resolution, whole-body fluid dynamic analysis of whales to date, according to the statement.
These calculations revealed that where the remoras choose to attach themselves to on the whale matters. Study co-author Erik Anderson, a biofluid dynamics researcher at Grove City College, says in the statement that when a remora is attached behind a whale’s blowhole, the suckerfish experiences half the force than it would in the free stream just centimeters above. However, remora’s suction disks have more than enough grip to withstand even the most turbid of placements on the whale’s body.
"We learned that the remora's suction disk is so strong that they could stick anywhere, even the tail fluke where the drag was measured strongest, but they like to go for the easy ride," Anderson says in the statement. "This saves them energy and makes life less costly as they hitchhike on and skim over the whale surface like a NASA probe over an asteroid."
The new research has exciting implications for underwater monitoring technology. Flammang wants to use the new insight on remoras’ sucking techniques to develop devices that can stick to whales and other animals more effectively than current technologies, which rely on glue and suction cups and can only stay on for about 24 hours, according to CBC Radio.
Marianne Porter, a biologist at Florida Atlantic University who was not involved in the study, told theTimes the researchers’ work was “a great example of how science should work—a question going from one place to another.”
The team plans to continue to study the flow environment of whales and the evolved mechanisms that certain species like remoras use to attach to hosts. They hope to use their findings to improve the tagging and tracking of whales for extended periods.
"It's an extremely arduous process to study whales what with permitting, research regulations and the game of chance of finding animals, all for the tags to usually fall off within 48 hours," says Flammang. "If we can come up with a better way to collect longer term data through better tag placement or better technologies, it could really advance our learning of the species, and many other animals that remoras attach to."