Plastics in the ocean don’t just look like a tasty meal to seabirds – they smell delicious too.
Researchers led by Matthew Savoca from the University of California, Davis in the US found microplastics in seawater emit a chemical irresistible to seabirds because it’s the same as a compound that signals that prey is nearby.
The study, published in Science Advances, explains why birds that rely on their sense of smell often end up with a belly full of plastic.
As of 2014, the oceans harboured a quarter billion metric tonnes of plastic – a number that’s rising each year. It’s no surprise, then, that marine life has been found gnawing on the stuff, with some 90% of seabirds accidentally eating it.
Seabirds in the order Procellariiformes – such as albatross and petrels – have a keen sense of smell and seem to be particularly affected.
They roam widely across the ocean, looking for signs of a chemical called dimethyl sulfide, which is produced by marine algae – especially when it is being nibbled on by little organisms such as krill. Krill is a favourite meal of many seabirds, and the scent of this compound tells them it’s time to eat.
Savoca and his colleagues thought plastic debris provided a handy growing platform for the algae that produced the compound. After a while, the plastic may take on the tasty chemical profile, attracting seabirds.
Birds that use dimethyl sulfide for finding food eat plastic more often – a rate almost six times as high as other seabirds.
So the researchers tied mesh bags of plastic beads made from three common plastics – which, together, comprise more than 60% of global plastic production – to a buoy for three weeks.
When they pulled them up again, dimethyl sulfide was found on every piece of plastic and at levels easily detectable by seabirds.
So while it was assumed that Procellariiformes eat plastic because it looks like food, chemical cues also appear to play a big part.
The research also suggests other animals that share similar diets, particularly those that eat crustaceans such as krill, might be attracted to the chemical signature that plastic debris takes on too.
Sea turtles, penguins, marine fish, and even mammals have all been shown to use this chemical for feeding in some way.
Not only are these animals in danger of eating too much plastic, they are being tricked into foraging in areas that don’t actually have many nutrients and missing out on real food.
The researchers hope that information on how plastic debris operates within marine food webs can help us understand why many marine animals are affected and how to mitigate the plastic problem – starting with creating plastics that cannot accumulate dimethyl sulfide.