Ocean Giants Could Be Significantly Threatened By Microplastics

Large filter feeders, like these manta rays, are likely to be at risk from microplastics. sergemi/Shutterstock

The mass of the plastic in the oceans right now can be compared to 17 Great Pyramids of Giza, and each year, another 550 Brooklyn Bridges’ worth is added. Make no mistake: plastic pollution is an ecological and environmental scourge.

One of the primary components of this waste are microplastics, sesame seed-sized beads that a plethora of marine life can accidentally ingest. An international team of researchers, led by the Marine Megafauna Foundation (MMF) and Murdoch University, use a new study to highlight the risks that microplastics may pose to large filter feeders, including baleen whales, whale sharks, and manta rays.

These animals strain particles suspended in the water column using a specialized structure. Plenty use this mechanism to eat plankton, but it’s been thought that microplastics – either as isolated particles or already in the digestive systems of prey they’re about to eat – could be posing a problem for these creatures too.

The team explain that their review of a recent studies emphasizes not just how prevalent microplastic is in marine ecosystems, but how little we currently understand about it. Although the extent of the biological effects of consuming microplastics isn’t yet clear, research has found that these polyethylene plastic particles are causing toxicity in fish and birds that eat them.

Filter feeders, which tend to have fewer offspring and live long lives, are likely to be at risk too; if these key species die off, this could seriously disrupt local food chains. Only a few studies looking into how microplastic threaten large filter feeders exist, though, and ultimately, more work is required to constrain these underreported and under-researched dangers. This paper serves as a rallying cry in that regard.

“Understanding the effects of microplastic pollution on filter-feeding megafauna is imperative because 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 prioritized for conservation,” the authors note in their study.

The paper also points out that sizeable filter feeders tend to gather in the Gulf of Mexico, the Bay of Bengal, the Coral Triangle, and the Mediterranean Sea, which are known to be microplastic “hotpots”. The team's review of recent data, published in the journal Trends in Ecology & Evolution, suggests that this means that microplastics could be regularly making their way through their filtration mechanisms.

Fin whales, for example, are estimated to eat up to 2,000 plastic particles per day.

A 2016 study focusing on these oceanic giants concluded that “exposure to microplastics because of direct ingestion and consumption of contaminated prey poses a major threat to the health of fin whales in the Mediterranean Sea.” As another example, the MMF that same year noted that preliminary findings, based on concentrations of microplastics, “suggest that mantas could be ingesting 40-90 pieces of plastic per hour of surface feeding in the locations studied.”

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