Chemical Waste From Plastic Pollution May Be Altering What Octopuses Eat

Images of turtles tangled in nets or fish suffocated by bags are the clearest signs that plastic pollution is harming our oceans. But plastic is not only dangerous because of its physical volume, it is also dangerous because of the chemicals it contains.

A new study has characterized how one of these chemicals, oleamide, modifies interactions between the South Florida common octopus (Octopus vulgaris) and its crustacean prey. The research showed that oleamide changed the way animals responded to each other, suggesting that the plastic chemical could change the structure of marine communities. The study was published in the Journal of Experimental Marine Biology and Ecology.

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What is oleamide?

Oleamide is a lubricant used to reduce friction in compounds such as polyethylene and polypropylene. But as these plastics break down, oleamide escapes. This is a problem for marine species, many of which naturally produce this compound.

The biological form of oleamide functions as a pheromone in marine species such as hermit crabs and is structurally similar to oleic acid which, according to a study conducted in Marine Pollution Bulletininfluences the reproduction of other crustacean species. If industrial oleamide reaches these creatures, it can interfere with their natural signaling systems.

“Many species rely on chemical information to detect food, assess predation risk, and balance trade-offs between foraging and safety,” Michael W. McCoy, an oceanographer at Florida Atlantic University and co-author of the new study, said in a statement.

How Oleamide Affects Octopuses and Their Prey

In the new study, McCoy and his team examined the octopus’ response to four prey species: hermit crabs, free-living crabs, snails and clams.

In the laboratory aquariums, the researchers presented the octopuses with their unfortunate prey. They monitored their interactions during 90-minute recording sessions, which tracked the octopuses’ proximity to their prey every 30 seconds. They also recorded what the octopuses ate over 24-hour periods. In total, the team recorded more than 30,000 predator-prey interactions.

If the octopuses successfully ate their prey, the team considered the interaction “successful predation.” If predators failed to consume their prey, grabbing it quickly and releasing it, the team considered the interaction “non-consumptive.”

The team explored how these interactions changed before and after adding oleamide to the aquarium. The team noted immediate changes, some of which persisted for more than 72 hours. Octopuses have increased the number of interactions with their prey. Although they did not consume more prey after the chemical was added, they appeared to change their preferred menu.

Oleamide interference to avoid predators

Before oleamide was added to the aquarium, the octopuses in the study showed a preference for crustaceans, opting for hermit crabs and hermit crabs over other prey. During and after exposure to oleamide, octopuses lost their taste for hermit crabs, which became almost as unpopular as their least preferred prey: snails.

What particularly surprised the researchers was the behavior of the prey species in the aquarium after exposure to oleamide.

“What is striking about this study is that when oleamide entered the system, this chemical communication seemed to break down. The crustacean prey reduced their predator avoidance behaviors, even though the octopus became more exploratory and increased its interactions, particularly grasping. Normally, greater contact with predators would strengthen the prey’s defenses. But in the presence of oleamide, this expected response simply did not occur,” McCoy said.

The researchers proposed that the chemical may be interpreted by crustaceans as a “foraging” signal, encouraging them to continue exploring their immediate surroundings even when threatening predators wave their tentacles nearby. The chemical may also interfere with animals’ ability to detect or escape predators.

Changing the predator/prey relationship

The fact that the octopuses did not eat more prey overall suggests that the chemical could alter the predators’ motor or hunting systems. The scientists proposed that oleamide may interfere with the chemical signals that octopuses usually deploy to detect nearby prey, and that the increase in non-consumptive interactions may reflect predators’ efforts to master their environment.

Although the exact mechanisms are unclear, these results suggest that if oleamide has a similar effect outside the laboratory in the wider oceans, the chemical could alter key behaviors in marine animals.

“These changes in predator-prey interactions could have profound effects on marine ecosystems,” Madelyn Hair, a study co-author currently working at the University of Colorado Boulder, said in a press release. “By altering how prey respond to predators and increasing non-consumptive interactions, oleamide leaching from plastics can ripple through entire marine communities. These subtle behavioral changes could reshape resource distribution and abundance, alter feeding dynamics, and affect interaction rates among multiple species, ultimately influencing the structure and function of coastal marine ecosystems in ways that we are only beginning to understand.”

Learn more: Octopuses detect invisible microbial signals to prevent food rotting

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