Microplastic pollution in world’s oceans poses major threat to filter-feeding megafauna
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Microplastic pollution in world’s oceans poses major threat to filter-feeding megafauna

EVEN as the world is waking up to the problems created by the massive amounts of plastic pollution in Earth’s oceans — and taking steps to address the issue — new research is shedding light on how detrimental that pollution is to marine wildlife.

A study published in the journal Trends in Ecology & Evolution last month, for instance, looks at how filter-feeding marine animals like baleen whales, manta rays, and whale sharks are impacted by microplastics. Filter feeders face exceptionally high risks of exposure to plastic pollution in the oceans because many of them are found in some of the most polluted waters in the world, such as the Bay of Bengal, the Gulf of Mexico, the Mediterranean Sea, and the Coral Triangle, a geographical region that lies in the waters between Indonesia, Malaysia, Papua New Guinea, and the Philippines.

2016 report by the Ellen MacArthur Foundation found that more than 8 million metric tons of plastic waste makes its way into the oceans every year, which works out to be roughly a garbage truck-full of plastic being dumped into the oceans every minute. What’s more, the report also determined that if we allow business-as-usual to continue, plastic pollution could find its way into our oceans at four times the current rate by 2050 — at which point the plastic in our oceans would weigh more than all of the fish combined.

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In response to this issue, more than 40 countries have joined the UN Environment Programme’s CleanSeas campaign, which was launched last year to combat the use of microplastics in cosmetics and single-use plastic products like shopping bags, two of the biggest sources of marine plastic litter.

But, according to Elitza Germanov, a researcher with the Marine Megafauna Foundation and a PhD student at Australia’s Murdoch University, while there is a growing body of research on how microplastics are impacting marine environments, few studies have specifically looked at how large filter feeders are effected.

“We are still trying to understand the magnitude of the issue,” Germanov, the lead author of the Trends in Ecology & Evolution study, said in a statement. “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.”

Filter-feeding megafauna like whale sharks and manta rays must swallow hundreds to thousands of cubic meters of water every day in order to catch enough plankton to keep themselves nourished. That means that these species are probably ingesting microplastics both directly from polluted water and indirectly through the consumption of contaminated plankton prey.

“The estimated daily plastic ingestion rates for filter-feeding megafauna vary greatly, depending on location and feeding behavior, and range from as low as 100 pieces for whale sharks in the Gulf of California to as high as thousands of pieces for fin whales in the Pelagos Sanctuary,” Germanov and co-authors note in the study. “Currently, the plastic ingestion rates by filter-feeding megafauna in the Gulf of Mexico, Bay of Bengal, and the Coral Triangle are unknown, as are the ingestion rates for mobulids anywhere in the world.”

Microplastic particles can block nutrient absorption and damage the digestive tracts of the filter-feeding marine life that ingest them, while toxins and persistent organic pollutants (POPs) found in plastic can accumulate in the bodies of marine wildlife over time, changing biological processes such as growth and reproduction and even leading to decreased fertility. Toxins that have bioaccumulated in long-lived filter feeders can also be passed down from mother to offspring. These effects can pose serious risks to animals that are already facing heightened threats to their existence.

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“It is vital to understand the effects of microplastic pollution on ocean giants since nearly half of the mobulid rays, two thirds of filter-feeding sharks and over one quarter of baleen whales are listed by the IUCN as globally threatened species and are prioritized for conservation,” Germanov said.

Germanov and co-authors note in the study that research has yet to directly confirm that filter-feeding megafauna are exposed to POPs and other toxins associated with plastics through the ingestion of microplastics. Because conventional methods used to study the diets of wildlife, like cutting open stomachs to examine their contents, are not suitable for species whose continued existence is already in peril, a more indirect approach must be taken.

“Most studies have now moved onto biopsies as strandings are rare and fisheries illegal or unethical for threatened species,” Germanov told Mongabay. She and her co-authors elaborate on the alternative methods available to researchers: “as the analytical approaches available to detect toxins continue to increase, it is possible to analyse small amounts of tissue obtained nonlethally (i.e., via biopsies) and to test for plastic chemical tracers, such as phthalates, organobromines, or specific congeners of POPs, allowing us to investigate correlations between microplastics in the feeding grounds of filter feeders and the exposure of these organisms to toxins.”


Manta rays swim with plastics in Indonesia. Source: Marine Megafauna Foundation

Sabrina Weiss, a public relations officer for the Marine Megafauna Foundation, noted in an email to Mongabay that while the definite causal link between plastic ingestion and resulting toxin exposure in marine megafauna has yet to be confirmed, “previous reports and laboratory studies in seabirds and small fish have already shown these connections.”

Study co-author Maria Cristina Fossi, of Italy’s University of Siena, was one of the first scientists to study megafauna filter-feeders and their exposure to microplastic pollution. She and her colleagues found an average of 0.7 plastic items per cubic meter of water around Mexico’s Baja California peninsula, an important feeding ground for endangered whale sharks, and estimated that whale sharks in the Sea of Cortez (also known as the Gulf of California, the body of water that separates mainland Mexico from Baja California) may be ingesting more than 170 plastic items every day. They’ve also estimated that fin whales in the Mediterranean Sea could be consuming thousands of microplastic particles on a daily basis.

“Our studies on whale sharks in the Sea of Cortez and on fin whales in the Mediterranean Sea confirmed exposure to toxic chemicals, indicating that these filter feeders are taking up microplastics in their feeding grounds,” Fossi said in a statement. “Exposure to these plastic-associated toxins pose a major threat to the health of these animals since it can alter the hormones, which regulate the body’s growth and development, metabolism, and reproductive functions, among other things.”

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While Fossi and colleagues’ previous research found that large filter-feeders like fin whales, whale sharks, and basking sharks are exposed to plastic-associated toxins and that there is evidence for plastic ingestion, Germanov told Mongabay that they did not show plastic in the stomach or guts of the species with POPs contamination.

What is clear at this point, according to Germanov, is that, with plastic production projected to increase globally, much more research is needed on the impacts of plastic pollution in the world’s oceans. She suggests that future research should focus on coastal regions where microplastic pollution overlaps with the feeding and breeding grounds of threatened species.

“Many areas are biodiversity hotspots and of economic importance due to fisheries and marine tourism,” she said. “Targeting these with the backing of local government and industry will help ensure efforts to mitigate the plastic threat are employed to their fullest.”

This article was originally published on Mongabay.