Oleamide From Plastic May Disrupt Marine Animal Behaviour

A seemingly harmless piece of plastic could alter how marine animals hunt, conceal themselves and stay alive. Scientists are increasingly finding that chemicals released by plastic rubbish may subtly disrupt undersea life in unexpected ways.

More than 350,000 chemicals are currently used worldwide. Plastic pollution carries many of them into the ocean. As plastic accumulates in coastal waters, it gradually gives off substances known as additives.

These additives may disrupt the chemical cues marine animals rely on to locate food, avoid predators, select secure habitats and communicate.

One compound attracting particular attention is oleamide.

Plastic chemical mimics natural signals

Manufacturers use oleamide as a lubricant in widely used plastics, including polyethylene and polypropylene. As plastic slowly fragments in water, oleamide leaks out.

Oleamide is not solely man-made: living organisms produce it too. In mammals, it influences sleep. For certain marine animals, it acts as a pheromone-a chemical signal used for communication.

It also closely resembles oleic acid, a chemical associated with death in species such as crabs.

Since oleamide resembles naturally occurring chemicals, marine animals may misread its presence. That misunderstanding could alter their behaviour.

Testing octopus behaviour

Researchers at Florida Atlantic University set out to examine how oleamide influences predator-prey behaviour.

Their study centred on Octopus vulgaris, a species frequently found in the waters of South Florida. This octopus feeds on smaller marine animals, including crabs and clams.

In laboratory tanks, scientists presented octopuses with four prey types: hermit crabs, free-living crabs, snails and clams. Cameras captured their behaviour in 90-minute sessions.

The researchers also monitored the octopuses’ food consumption over 24 hours. Altogether, they analysed more than 31,500 observations.

The team classified predator-prey encounters into three categories: successful hunts, failed attempts and brief grasps. Failed attempts and brief grasps were defined as non-consumptive interactions.

What changed in the water

Before oleamide was introduced, octopuses showed a clear preference for crustaceans. They selected hermit crabs and free-living crabs more often than clams or snails. Snails were the least preferred food throughout the study.

Once scientists added oleamide to the water, the octopuses’ behaviour shifted rapidly. They selected more free-living crabs and fewer hermit crabs.

This change persisted for at least three days after the chemical was removed. Hermit crabs were selected less often than clams, something that had not previously occurred.

Encounters between the octopus and its prey also became more frequent. Yet successful hunts did not increase. Instead, failed attempts and brief grasps occurred more often.

When communication breaks down

Scientists think oleamide could confuse crustaceans. It may resemble oleic acid, which acts as a death signal in some species. As a result, prey may keep foraging rather than taking steps to avoid danger.

“Many species rely on chemical information to detect food, assess predation risk, and balance the tradeoffs between foraging and staying safe,” said Dr. Michael W. McCoy, senior author of the study.

“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.”

The octopus itself may be confused as well. Octopuses detect prey using chemical signals in the water and through touch. Oleamide may disrupt this capacity, producing more contact without increasing successful hunts.

Broader implications of the oleamide study

Small shifts in behaviour can still affect an entire ecosystem. Food chains may change if prey do not avoid predators effectively. Increased contact among species can also alter how energy passes through the system.

“These changes in predator-prey interactions could have far-reaching effects on marine ecosystems,” said Madelyn A. Hair, first author and a research lab manager for the Gil Lab at University of Colorado Boulder.

“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.”