Article body copy
Even a crafty hunter like an octopus sometimes needs help. On tropical coral reefs around the world, the day octopus scours the seafloor in search of tiny mollusks and crustaceans that hide within calcified crevices. But every so often, this prey eludes the octopus’s many-armed grasp. Unfortunately for the fleeing prey, groups of fishes—sometimes four or five different species—might be lying in wait, ready to cut off its escape and leaving it within the octopus’s reach.
For the octopus and the fish, it may seem like harmonious cooperation. But on this team, everyone plays an important part and must invest effort in capturing prey. If a fish joins the group and doesn’t pull its weight, the octopus can eject it from the group with a swift punch.
According to Eduardo Sampaio, a doctoral candidate at the University of Lisbon in Portugal and lead author on a new study documenting the behavior, there are a number of reasons an octopus might throw hands, from keeping its hunting partners in line to ejecting a parasitic group member.
Goatfish, for example, are active hunters that create prey opportunities for the octopus and the rest of the group, while blacktip grouper are ambush predators that hide and wait for prey to pass by. Sampaio says the octopus might view the goatfish as a collaborator, while viewing the blacktip grouper as a competitor that needs to be ejected.
“These hunting groups are complex. Every member has a different hunting strategy and a different level of investment,” says Sampaio. “In a situation like this, we would expect partner control mechanisms to evolve to help ensure a more fair distribution of payoff.”
To record octopuses’ outbursts, Sampaio and his collaborators followed hunting groups with underwater camera rigs capable of capturing a three-dimensional view of the reef and the positions of the animals within it.
Sampaio says his ultimate goal is to use this footage to tease apart the group dynamics that come before and after the punching behavior to better understand how it evolved.
“There’s just amazing natural history in this behavior,” says Redouan Bshary, a marine biologist at the University of Neuchâtel in Switzerland who is not affiliated with this study. Bshary’s research has explored similar hunting groups, such as the collaboration between grouper and moray eels. He says grouper chase prey into crevices, and eels signal to the grouper before they dive into those crevices. However, eels lack the appendages required to punch their collaborators.
While there is much left to learn about the octopus’s behavior, documenting it is a big step forward, says Sampaio. “First, we had to find octopuses, which is difficult … Then we had to find octopuses hunting with fish, which is even rarer.” Octopuses are known to forge alliances with other species to find food, but it is far from common.
Chelsea Bennice, an octopus biologist at Florida Atlantic University who is not associated with the research, has never seen direct evidence of collaborative hunting behavior in octopuses, but says she has witnessed that they tend to swat at trailing fish that approach too closely. This seems to suggest that the punching behavior also exists outside of collaborative contexts as a mechanism of pure competition.
Daniel Bayley, a marine biologist at University College London in England who is not involved with the work,* suggests climate change may be playing a role in driving these unlikely hunting groups together. After significant coral reef bleaching events, Bayley says he has documented sightings of collaborative hunting between octopuses and fish on reefs where the behavior had never before been recorded, suggesting the possibility that this might be an adaptive strategy to deal with limited food resources.
When prey becomes scarce, the thin line between collaboration and competition begins to blur.
*Correction: This sentence erroneously said Daniel Bayley was involved with the research.