"Olfactory trap" lures sea turtles into eating plastic waste
One of the real and dangerous consequences of plastic waste making its way into ocean is the increasing threat it poses to marine life. Sea turtles are one example of a creature that regularly consume these pieces of trash for dinner, and a new study offers up new answers as to why, revealing that they can mistake the smell of plastic for food as part of what scientists describe as an “olfactory trap.”
The amount of plastic trash that is pouring into the ocean, estimated to be millions of metric tons every year, is more than a nuisance for the marine life that call this environment home. Some studies have estimated that as much as 52 percent of the global sea turtle population have consumed some form of plastic. One study from the CSIRO in Australia found that a turtle that has consumed just a single piece of plastic had a 22 percent chance of dying from it, while that probability increased to 50 percent when they had 14 plastic items in their bellies.
So whether it's a plastic bag they are mistaking for a jellyfish or fishing net they see as seaweed, sea turtles are consuming and becoming tangled in plastic waste with troubling regularity. While scientists have thought for some time that this is because they incorrectly see these items as food, not so much was understood about how their senses drive these behaviors.
To learn more, scientists from the University of Florida and Stanford University conducted experiments where 15 young loggerhead turtles raised in captivity were recorded on video reacting to different stimuli. The researchers had previously established that the same odors sea turtles rely on to track down food can also arise from biofouled plastic debris, meaning trash that has accumulated microbes, algae and plants on its surface can give off the same stench.
The experiments were therefore designed to see if the turtles could differentiate between waste and food using only their noses. The team fed odors through a pipe into tank that ranged from deionized water and clean plastics for control, to shrimp meal, fish and biofouled plastic.
The team found that the turtles reacted to the biofouled plastic the same way they reacted to food, keeping their nostrils above the water for three times longer than the control odors to properly take in the scent.
"We found that loggerhead sea turtles respond to odors from biofouled plastics in the same way they respond to food odorants, suggesting that turtles may be attracted to plastic debris not only by the way it looks, but by the way it smells," says Joseph Pfaller of the University of Florida, Gainesville. "This 'olfactory trap' might help explain why sea turtles ingest and become entangled in plastic so frequently."
These findings mirror those from a 2016 study, in which scientists found that seabirds such as albatross and petrels can often mistake plastic debris in the ocean for the food they typically eat due to the stench it gives off. The authors of this latest study hope to learn more about these processes by studying the chemicals that give plastic debris the ability to attract marine life in this way.
"The plastic problem in the ocean is more complex than plastic bags that look like jellyfish or the errant straw stuck in a turtle's nose," Pfaller said. "These are important and troubling pieces to the puzzle, and all plastics pose dangers to turtles."
The research was published in the journal Current Biology.
Source: Cell Press via EurekAlert