Death from a belly full of garbage – why do sea turtles swallow so much sea plastic? The plastic parts apparently not only look like food, but also smell like it, according to a study: According to this, layers of algae and microorganisms form on the plastic surfaces, which make the material “smell” like food. Experiments show that when sea turtles perceive this smell when taking a breath, they start looking for food.
Remnants of plastic bags and all kinds of plastic – meanwhile ugly relics of civilization are everywhere. And it gets worse and worse: every year, millions of tons of waste end up in the oceans and threaten ecosystems. Numerous studies have already shown how dangerous the plastic parts are for many marine animals: some consider them to be food and swallow the garbage. The indigestible foreign bodies then settle in the animal’s digestive system and can lead to death.
What is so tempting about the plastic parts?
The sea turtles are particularly affected: Studies have shown that they often die or get caught in swallowed plastic waste. So far, it has been assumed that the animals snap at the plastic structures because they look something like their food objects. In view of the extent of the problem, the question arose whether, in addition to the sense of sight, other turtle perception systems also respond to the plastic parts and contribute to the fatal attraction of the garbage. The sense of smell also came into consideration. Because it is known that especially young sea turtles look for food when they appear in the surface area and are based on smells.
As part of their study, the researchers led by Joseph Pfaller from the University of Florida at Gainesville have now carried out odor tests on 15 loggerhead turtles (Caretta caretta) kept in captivity. This species is the most common representative of these marine reptiles. During the tests, the young experimental animals were in a container into which odorants could be passed through a pipe. The smells in the tests included a pure “water breeze” as a control and the volatile substances from the usual turtle feed. In further runs, the animals were then confronted with the smell of clean plastic pieces and finally with the aroma of similar parts that had been in the water for a week. As the researchers explain, a biofilm of algae and marine microorganisms had formed on the plastic pieces during this time.
Reactions like the smell of food
As the researchers report, the video recordings showed the behavior of the turtles: The animals reacted to the smell of the overgrown plastic parts in the same way as to the scent of their food. Compared to the controls, the turtles kept their nostrils out of the water more than three times longer to get a good dose of air. The scientists also reportedly started looking for feed. “We were surprised that the turtles reacted to the smells of the overgrown plastics with the same intensity as to their usual food,” said Pfaller. “We have now been able to demonstrate that turtles are not only attracted to the appearance but also to the smell of plastic waste,” summarizes the scientist.
According to him and his colleagues, the smell may not only be a fatal temptation for turtles – marine mammals, fish and birds could also react in a similar way to the evaporation of overgrown plastic. “There are huge areas in parts of the Pacific Ocean that are covered with floating plastic waste,” said senior author Kenneth Lohmann of the University of North Carolina at Chapel Hill. “The study now fears that the concentration of plastics could cause turtles – or other animals – to suspect that there is an abundance of food there,” said the scientist.
He and his colleagues therefore see a further appeal to everyone in their study results to help reduce marine garbage pollution: unnecessary plastic packaging should be avoided, waste separation and recycling are the order of the day. “Once plastics are in the ocean, we no longer have a good way of removing them or preventing them from smelling attractive. So the best thing is to prevent plastic from getting into the ocean at all, ”says Lohmann.
Source: Cell Press, Current Biology, doi: 10.1016 / j.cub.2020.01.071