These fish are also prey to fish that humans consume, which means that microplastics could indirectly contaminate our food supply through the transfer of associated microplastic toxins.
Microplastics are small fragments of plastic that have accumulated in the marine environment after decades of contamination. These fragments can cause significant problems for marine organisms that ingest them, including inflammation, reduced feeding and weight loss.
Microplastic contamination can also spread from organism to organism when predators eat prey. Since fragments can bind chemical contaminants, these associated toxins could accumulate in predator species.
Mesopelagic fish serve as a source of food for a wide variety of marine animals, such as tuna, swordfish, dolphins, seals and seabirds. They usually live at depths between 200 and 1,000 meters, these fish swim to the surface at night to feed and then return to deeper waters during the day.
Through these vertical movements, mesopelagic fish play a key role in the carbon and nutrient cycle from the surface to the depths of the sea, a process known as the biogeochemical cycle. This means that they could spread microplastic contamination throughout the marine ecosystem, transporting microplastics from the surface to deeper waters, affecting deep-water organisms.
The mesopelagic fish, little studied
Despite its important role in marine ecosystems, mesopelagic fish have been relatively little studied in the context of microplastics. To investigate further, Wieczorek and his colleagues set out to capture fish in a remote area of the northwest Atlantic Ocean: a whirlpool off the coast of Newfoundland.
"These fish inhabit a remote area, so theoretically they should be quite isolated from human influences, such as microplastics , but since they migrate regularly to the surface, we think they could ingest microplastics there," explains Alina Wieczorek, of the National University of Ireland, lead author of the study.