More than 350,000 chemicals are used worldwide, and many find their way into the ocean through plastic pollution. As plastics accumulate in coastal waters, they continuously leach bioactive additives that can interfere with the chemical cues marine animals rely on to find food, avoid predators, choose habitats and communicate.
One such chemical, oleamide, is an industrial lubricant in plastics like polyethylene and polypropylene. As these plastics degrade, oleamide seeps into the water. But it's not just industrial: oleamide is naturally produced by many organisms and influences sleep in mammals, acts as a pheromone in some marine species, and closely resembles oleic acid – a cue tied to death and scavenging in arthropods like crabs. By mimicking natural signals, oleamide may quietly alter how marine life senses food and interacts with one another.
To understand these effects, Florida Atlantic University researchers studied how plastic-derived oleamide influences predator-prey behavior. They focused on a common South Florida octopus (Octopus vulgaris), a key mesopredator, and observed its responses to four widespread prey: hermit crabs, free-living crabs, snails and clams.
In controlled laboratory aquariums, each octopus was offered the four native prey. Researchers tracked what was eaten over 24-hour periods and monitored the proximity of prey to the octopus during 90-minute sessions using video scans every 30 seconds. They then analyzed more than 31,500 individual observations across all prey types.
Predator-prey interactions were classified as successful predation, failed attempts or brief grasps, with the latter two grouped as "non-consumptive." To see if oleamide affected prey choice, researchers used a scientific measure of preference before, during and after exposure.
Results of the study, published in the Journal of Experimental Marine Biology and Ecology , reveal that exposure to the plastic additive oleamide caused immediate changes in octopus prey choice, predator-prey proximity, and predator-prey interactions – some lasting at least three days. Even after the chemical was removed, overall attacks declined but non-consumptive interactions stayed high, showing that oleamide's effects can linger, subtly reshaping behavior and ecosystem dynamics.
Before oleamide exposure, all octopuses preferred crustaceans, selecting both hermit crabs and free-living crabs more than other prey. During active exposure, however, they increased their selection of free-living crabs while decreasing their selection of hermit crabs. Notably, this shift persisted, with hermit crab selection dropping below that of clams. Snails consistently remained the least-preferred prey throughout the study.
"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 , Ph.D., senior author, associate director, FAU School of Environmental, Coastal, and Ocean Sustainability , and professor of quantitative ecology, Department of Biological Sciences , FAU Charles E. Schmidt College of Science and FAU Harbor Branch Oceanographic Institute . "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."
Findings suggest that oleamide may be misinterpreted by crustacean prey as oleic acid. This misinterpretation appears to encourage prey to continue foraging despite the presence of a predator, increasing predator-prey proximity and elevating predation risk. Oleamide may also interfere with the prey's ability to detect predator cues or appropriately respond to them, further reducing predator-avoidance behaviors.
Interestingly, although predator-prey interactions increased during oleamide exposure, the number of successful predation events did not rise. Instead, non-consumptive interactions – such as failed attempts and brief grasps – were more frequent. This pattern may reflect effects on the octopus itself, including potential reductions in motor function or hunting motivation, or it may simply result from increased opportunities for interaction due to prey spending more time near the predator. Additionally, octopuses rely on both waterborne and contact chemical cues to detect prey, so oleamide could have confused or disrupted their chemosensory abilities, prompting increased exploratory behavior and physical contact with prey to gather more information.
"These changes in predator-prey interactions could have far-reaching effects on marine ecosystems," said Madelyn A. Hair, first author, a graduate alumna from FAU Harbor Branch, and a research lab manager for the Gil Lab at University of Colorado Boulder, Department of Ecology and Evolutionary Biology. "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."
Study co-authors are Chelsea O. Bennice , Ph.D., a research fellow at FAU's Marine Laboratory within the Charles E. Schmidt College of Science, and Krista A. McCoy, Ph.D., director of research and conservation at Florida Oceanographic Society.
This work was supported by internal funding from FAU and FAU Harbor Branch and by a grant from the Conchologists of America, Inc.
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About Florida Atlantic University:
Florida Atlantic University serves more than 32,000 undergraduate and graduate students across six campuses along Florida's Southeast coast. Recognized as one of only 13 institutions nationwide to achieve three Carnegie Foundation designations - R1: Very High Research Spending and Doctorate Production ," " Opportunity College and University ," and Carnegie Community Engagement Classification - FAU stands at the intersection of academic excellence and social mobility. Ranked among the Top 100 Public Universities by U.S. News & World Report, FAU is also nationally recognized as a Top 25 Best-In-Class College and cited by Washington Monthly as "one of the country's most effective engines of upward mobility." To learn more, visit www.fau.edu .
