Litter that smells like food
It is well known that marine litter negatively impacts the marine environment. This litter, composed mainly of plastics, threatens many marine organisms through entanglement or ingestion, being a major cause of mortality and injuries.
The reason why marine fauna is attracted to marine litter has typically been attributed to confusion: a plastic bag in the water can look like another marine organism (jellyfish, cephalopod, etc.) and that’s why it is ingested. Despite this, the ingested litter is neither made up exclusively of plastic bags nor it looks always similar (at least apparently) to another marine organism. This fact questions that the only reason for the interaction between marine fauna and litter is caused by a visual mistake. Another sense could also play a very important role: smell.
The role of smell in attracting marine species to litter has been tested in a study focused on the loggerhead sea turtle (Caretta caretta) that was carried out in the United States. In that study, the reaction and behavior of the sea turtles when perceiving airborne odorants of four different elements (deionized water, turtle food, clean plastic (fragments of a plastic bottle) and biofouled plastic (fragments of a bottle of plastic that was exposed to biofouling for 5 weeks in the marine environment)) was studied. The different odorants were delivered separately to assess the behavior of the turtles in each case, having the same response when food and biofouled plastic odorants were emitted. In both cases, sea turtles adopted what was considered a foraging behavior.
This fact had previously been demonstrated in other studies focused on seabirds, showing that biofouled plastic litter emanates airborne odorants that marine predators use to identify prey and high production areas in the ocean. Therefore, it seems that the interaction between some marine species and litter is not exclusively caused by visual confusion. Unfortunately, marine litter smells like food.
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