Published in the Trends in Ecology and Evolution journal, a new study took a look at the possible effects of microplastics on filter-feeding animals. It determined that baleen whales, whale sharks, basking sharks, and rays might be in danger from potential toxins.
As their name suggests, filter feeders use specialized body parts to filter food from seawater. Some of them can gulp great amounts of seawater in one big go while others constantly run water through the natural sieves in their bodies. Unfortunately, their every swallow exposes them to ever-increasing amounts of microplastics that contaminate the world's oceans.
The Gulf of Mexico, the Mediterranean Sea, the Bay of Bengal, and the Coral Triangle are laden with microplastic pollutants. They also happen to be the favorite feeding grounds of many filter-feeding megafauna. (Related: The plastic pollution problem is wide AND deep: Study finds sea animals from the deepest parts of the ocean, 7 miles down, have plastic in their stomachs.)
According to Elitza Germanov, co-author of the study and a Marine Megafauna Foundation researcher, microplastics pose an insidious threat because there is so little information about their effects on sea-life that ingest them.
“Despite the growing research on microplastics in the marine environment, there are only a few studies that examine the effects on large filter feeders. We are still trying to understand the magnitude of the issue," she admitted.
"It has become clear, though, that microplastic contamination has the potential to further reduce the population numbers of these species, many of which are long-lived and have few offspring throughout their lives,” Ms. Germanov warned.
Many species of filter-feeders are already endangered due to overfishing, pollution, bigger chunks of plastics, and other threats. The authors of the research study worry that microplastics would worsen filter-feeders' plight and possibly lead to their deaths as a species.
While the exact process by which microplastics can poison megafauna remains vague, Ms. Germanov and her co-author Maria Cristina Fossi remain convinced that microplastics were just as toxic as their larger versions.
Why we know so little
In an interview with The Guardian, Professor Fossi explained the difficulty of studying the affected animals.
Many filter-feeders like whale sharks, basking sharks, and baleen whales are threatened species to begin with. Their long lives, small populations, and low reproductive rates make it difficult for them to recover from losses. In addition, a good number of the filter-feeders happen to be big animals. Whales are among the largest animals in history while the whale shark is the biggest species of shark and fish. So, inspecting the stomach of a dead specimen is not very feasible.
Professor Fossi believes microplastics exert possible “sub-lethal effects” on wildlife. She cited earlier research on whale sharks and fin sharks that confirmed their exposure to high levels of microplastics.
BBC reported that whale sharks in the heavily-polluted Sea of Cortez off Mexico's Baja Peninsula end up eating at least 200 pieces of plastic each day. On the other side of the world, fin whales in the Mediterranean Sea swallow 2,000 microplastic particles per day.
“Exposure to these plastic-associated toxins pose a major threat to the health of these animals since it can alter the hormones,” Professor Fossi told The Guardian.
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