Chemical Waste From Plastic Pollution May Be Altering What Octopuses Eat

Images of turtles tangled in nets or fish choked by bags are the most obvious signs that plastic pollution is harming our oceans. But plastic isn’t just dangerous because of its physical bulk, it’s also dangerous due toe to the chemicals it contains.

A new study has characterized how one of these chemicals, oleamide, alters interactions between the common South Florida octopus (Octopus vulgaris) and its crustacean prey. The research showed that oleamide altered how animals responded to one another, suggesting that the plastic chemical could alter 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 that is used to reduce friction in compounds such as polyethylene and polypropylene. But as these plastics break down, oleamide leaks out. This is a problem for marine species, many of which produce the compound naturally.

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 in Marine Pollution Bulletin, influences reproduction in other crustacean species. If industrial oleamide reaches these creatures, it may interfere with their natural signaling systems.

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

How Oleamide Impacts Octopuses and Their Prey

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

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

If the octopuses successfully chowed down on their prey, the team scored the interaction as a “successful predation.” If the predators instead failed to consume their prey, quickly grasping it and letting it go, the team scored the interaction as “non-consumptive.”

The team explored how these interactions changed before and after oleamide was added to the aquarium. The team noted immediate changes, some of which persisted for more than 72 hours. The octopuses increased the number of interactions they had with prey. While they didn’t consume more of the prey after the chemical’s addition, they seemed to shift their preferred menu.

Oleamide’s Interference With Avoiding Predators

Prior to oleamide’s addition to the aquarium, the octopuses in the study showed a preference for crustaceans — opting for free-living and hermit crabs over other prey. During and after oleamide exposure, the octopuses lost their taste for hermit crabs, which became almost as unpopular as the least favored prey option — snails.

What was particularly surprising to the researchers was how the prey species in the aquarium behaved after exposure to oleamide.

“What’s striking about this study is that when oleamide entered the system, that chemical communication appeared to break down. Crustacean prey reduced their predator-avoidance behaviors, even as the octopus became more exploratory and increased their interactions, especially grasps. Normally, more predator contact would heighten prey defenses. But in the presence of oleamide, that expected response simply didn’t happen,” said McCoy.

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

Changing the Predator/Prey Relationship

The fact that the octopuses didn’t eat more prey in total suggests that the chemical may alter the predators’ motor or hunting systems. The scientists proposed that oleamide may be interfering with the chemical cues that the octopuses usually deploy to detect nearby prey, and that the increase in non-consumptive interactions may reflect the predators’ efforts to get a grip on their surroundings.

While the exact mechanisms aren’t clear, these findings suggest that, if oleamide has a similar effect outside the lab in the wider oceans, the chemical could alter key behaviors of marine animals.

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

Read More: Octopuses Pick Up On Invisible Microbial Cues to Avoid Rotting Food

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