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Full Story: National Geographic (9/24), ScienceAle
The hunt was going well—until one fish got out of line. In a sudden flash of black and white, the color-changing octopus whipped out its arm and—whack—landed a punch. The fish, a blacktip grouper, obliged, returning to its place in the group of predators in search of a meal.
Scientists first observed this comical behavior among day octopus in 2018 and 2019 in the Red Sea, which intrigued National Geographic Explorer Eduardo Sampaio.
“One of the main questions last time was: Is this really collaboration, or are the fish just following the octopus around?”
To find out, Sampaio and colleagues recently set up two camera rigs to follow and film these Red Sea hunts, which they later reconstructed with computer software. After reviewing over a hundred hours of footage, the team is confident that day octopuses are indeed enforcing teamwork between the hunters, which often consist of a single octopus and between two to 10 fish. (Learn eight fascinating facts about octopuses.)
“The active predators, like the goatfish, are the ones that find the food,” while the octopus “basically unlocks the food for everyone,” says Sampaio, a postdoctoral researcher at the University of Lisbon in Portugal and Max Planck Institute of Animal Behavior.
“If the group is moving, everyone’s happy. It’s all good,” he says. But sometimes troublemakers, like blacktip groupers, gum up the works. Because these ambush predators usually wait for prey to come to them, their lack of movement can slow down the hunt.
“Half of the times [a grouper is] present, it’s getting punched,” says Sampaio, whose study appeared September 23 in Nature Ecology & Evolution. “So, it’s clearly an animal that the octopus understands is not collaborating.”
Reef ‘bulldozer’
But not all experts are knocked out by this new theory.
“Did Eduardo see something that the rest of us missed?” Jennifer Mather, an octopus cognition expert at Canada’s University of Lethbridge who wasn’t involved in the study, says in an email.
Mather describes hunting octopuses “like a bulldozer”: They “roil up the area” and scare animals off in all directions.
Previous studies—including her own—suggest other predatory fish are “dependent ‘followers’ that take advantage of the octopus’ disturbance of the environment,” says Mather. For instance, “fish often go in front and wait to see what runs from the bulldozer,” she says. (This octopus defends its space—by throwing things.)
During her research, Mather has seen a common octopus slapping a scavenging fish when it came too close. She’s also watched a damselfish attack an octopus.
What’s more, she believes the researchers should be looking at the direction the fish are facing, not their location in the group. Leaders in a cooperative hunt “would have pointed away from the octopus and scavengers pointed towards it,” she says.
Alexandra Schnell, a National Geographic Explorer and visiting research associate at the University of Cambridge in the U.K., says it’s not that simple.
“The octopus’s ability to flush out prey affects how other fish interact with the group, even if it’s not always at the front,” Schnell, who wasn’t involved in the study, says via email.
Although more research is needed, it’s not far-fetched to think the fish and octopus have learned to hunt together for mutual benefit, she says.
In the videos, some of the octopuses spread out their arms over a rock or coral reef for long periods, a sign that they have trapped prey, such as smaller fish, the study authors say.
Mather, again, doesn’t agree: She thinks octopuses may just be checking out chemicals left by prey fish.
Teamwork makes the dream work
If Sampaio’s hypothesis is right, an octopus saves energy by working with fish: Together, the predators can explore a larger area more quickly than if they were alone. For the octopus, this frees up more time for other activities, such as reproduction, social interaction, playing, and building or maintaining a den.
Other examples exist of animals enforcing behavior in cooperative situations.
“In cleaner fish species, such as cleaner wrasse, males may punish females if they take bites from their clients, which are supposed to be cleaned rather than eaten,” says Schnell.
The study reveals the octopuses’ “capacity for complex social interactions and role differentiation within a group,” she says. (Read why octopuses remind us so much of ourselves.)
Curiosity abounds
Many questions remain. Are these animals collaborating or, as Mather suggests, “just in the same place at the same time?”
Sampaio is curious if the octopuses’ black-and-white coloration is a warning sign to the fish, a way of saying: “You are annoying me already!” He also wants to know if the fish understand this cue and then behave differently.
Another mystery is whether an octopus can distinguish individual fish, many of which live for decades. “Do they know that it’s… Steve or Martha, and they really like to hunt with Steve and Martha?”
Though all researchers might not be aligned on these findings, they agree on one thing—they want to know more.
As Mather says, “It’s a puzzle and scientists get curious—that’s our job.”
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