Seabirds are often found to have stomachs stuffed full of plastic they have ingested having mistaken fragments and particles of polymeric flotsam for food. One might assume that the unfortunate birds are simply attracted to the appearance of plastic food packaging and other debris. However scientists suspect there is something else that attracts ocean-faring birds to feast on such flotsam.
Research carried out at the University of California, Davis by two graduate students, Matthew Savoca, Martha Wohlfeil, with Professors Susan Ebeler and Gabrielle Nevitt suggests a far subtler effect is at play and might explain why certain species of tube-nosed seabirds, including petrels, shearwaters, are prone to ingest plastic. The researchers have demonstrated that biofouling can occur on plastic experimentally deployed at sea and that the algal coating emits dimethyl sulfide (DMS). Certain species of seabird have a species-specific response to DMS and that this is linked to different types of foraging strategies. [Savoca et al. Sci Adv (2016); 2(11), e1600395; DOI: 10.1126/sciadv.1600395]
"It's important to consider the organism's point of view in questions like this," explains Savoca. "Animals usually have a reason for the decisions they make. If we want to truly understand why animals are eating plastic in the ocean, we have to think about how animals find food." Insights into why seabirds and marine organisms, such as fish and turtles are repeatedly dining on plastic rather than food might lead to new solutions to this highly troubling form of pollution.
To sniff out the smell of marine plastic debris, the team tested beads of high-density polyethylene, low-density polyethylene, and polypropylene placed in the ocean off the California coast and sought the assistance of Ebeler of the Department of Viticulture and Enology. The team could analyze the sensory-response data with respect to published data on plastic ingestion collected from many different investigators. "The study shows that species that have been shown to respond to DMS at sea also consume a lot of plastic, when corrected for sampling effort," Nevitt told Materials Today. Savoca and Wohlfeil also demonstrated that the biofouled plastic is emitting DMS. "Previous work conducted by me and collaborators at CNRS in France have shown that some of these species can detect DMS at concentrations that are well below the concentrations that the biofouled plastics are emitting," Nevitt adds. "So all the pieces of the puzzle fit together."
Nevitt and co-workers had also previously demonstrated that DMS is commonly released by animals, such as krill, that have themselves ingested algae. The researchers explain that while plastic coated with algae does not smell like actual food, it does smell like food being eaten. The study suggests that seabird species that use the odor of DMS to help them find prey are nearly six times more likely to eat plastic than those that do not.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".