A team of scientists at the University of California believes they have figured out why seabirds eat plastic trash they find floating in the ocean. Published in the journal Science Advances, the new study revealed that a common kind of algae emits dimethyl sulfide (DMS), a chemical that is released when krill gobble up the algae. Seabirds feed on krill, and it is evident to them that there is prey around when they smell the chemical, so they eat the krill and the plastic the algae are floating on.
The researchers found that plastic trash in the ocean usually accumulates algae as well as other organic matter on its surface. The process is known as biofouling. Millions of tons of plastic waste end up in the ocean each year.
The chemical really stinks up the place, and that is irresistible for seabirds such as shearwaters, which cannot tell apart algae from plastic that smells just the same. Biologist Matthew Savoca and his fellow researchers figured out why seabirds ate plastic by putting plastic bags to float around in the ocean for three weeks and then taking them to the university’s food and wine laboratories to track the chemicals contained in the plastic.
The bags had been filled with high-density polyethylene, low-density polyethylene, and polypropylene, which are three of the most common types of plastic debris. The researchers had attached the trash to buoys in the ocean. Once they analyzed the chemicals contained in the plastic trash, they were able to discover that all of it actually reeked of that sulfur compound because of the algae that got in touch with it when it was floating on the sea. Unlike the plastic that had not been soaked in the ocean, the scientists identified a DMS signature on all of the plastic that had been in the sea for three weeks.
Marine ecologist Chelsea Rochman at the University of Toronto explained that plastic is so harmful to any living thing because it is made of chemicals not meant to be eaten. It also quickly absorbs many of the chemicals contained in oil and those washing off from pesticides, and flame retardants, among other industrial pollutants, National Public Radio reported.
It is interesting to note that not all birds are attracted by DMS. By pooling data from previous studies on seabirds who consume plastic, the researchers found that those birds known to be attracted by DMS eat plastic five times as frequently compared to species which are not responsive to the chemical.
Both Rochman and Savoca believe that fish and other marine animals might also be eating the plastic for the same reason as seabirds, which could be harmful to people who consume marine food.
Plastic ingestion by animals could also be attributed to other things
Scientist Chris Wilcox, who was not involved in the research, told The Washington Post in an email that this paper “provides a convincing argument for the Procellariiform seabirds as to why they might pick up plastic from the ocean.” He is a senior research scientist at the Commonwealth Scientific and Industrial Research Organization in Australia.
Nevertheless, he pointed out that other non-DMS-responsive species have also shown evidence of plastic ingestion. Many species could make a mistake due to visual factors, and this may even include seabirds which are attracted by DMS, Savoca noted.
“I think it’s quite possible that these hypotheses are complementary, they really build on each other,” Wilcox said in the email. “If something looks like food and smells like food, it would be much harder not to eat it.”