Microplastics Pose a Significant Risk to Whales, Manta Rays and Whale Sharks

microplastics threaten giant sea creatures

Story at-a-glance -

  • The consumption of microplastics is putting baleen whales, manta rays and whale sharks, which eat by filtering ocean water in search of tiny plankton, at significant risk
  • Filter-feeding ocean giants are exposed to microplastics directly when they filter the water to feed as well as indirectly via plastic chemicals and their food sources, which may also eat plastics
  • While it’s unknown if consuming microplastics could prove lethal to a large filter-feeder, it’s likely that they could cause “sub-lethal effects” that harm the animal’s health

By Dr. Karen Becker

It's an amazing feat of nature that the largest creatures on Earth survive by eating some of the smallest. This is especially true of baleen whales, manta rays and whale sharks, which eat by filtering ocean water in search of tiny plankton. But as they filter the water in search of food they're also ingesting other tiny fragments that are now ubiquitous in oceans worldwide: microplastics.

Microplastics are defined as those that are less than 5 millimeters in length. They can come from large plastic debris that gets broken down into small pieces, as well as microbeads, which are tiny pieces of plastic added to personal care products such as exfoliants and toothpaste.

When you wash these products down your drain, the microbeads travel right through wastewater treatment plants, as they're too small to be caught by the filters. Filter-feeding ocean giants, in turn, are exposed to microplastics directly when they filter the water to feed as well as via their food sources.

A variety of marine life, from plankton to fish to seabirds, are known to consume microbeads, for instance, as they resemble fish eggs. While microbeads were banned from personal care products and cosmetics in the U.S., they've been in use for about 50 years,1 giving them plenty of time to accumulate in the ocean — and they're still in use in some countries around the globe.

Microplastics Further Threaten Filter-Feeding Giants

Half of the species of mobulid rays, along with two-thirds of filter-feeding shark species and more than one-quarter of baleen whale species are listed as threatened species by the International Union for the Conservation of Nature (IUCN).2

Already stressed by overfishing, pollution and other manmade hazards, the consumption of microplastics is putting these creatures at even further risk, according to a recent study published in Trends in Ecology & Evolution.3 Study author Elitza Germanov, researcher at the Marine Megafauna Foundation and Ph.D. student at Murdoch University in Australia told Phys.org:4

"Despite the growing research on microplastics in the marine environment, there are only few studies that examine the effects on large filter feeders. We are still trying to understand the magnitude of the issue. 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."

While beached whales have been found with large plastic debris in their stomachs, studying the exposure to microplastics is more difficult. However, researchers are able to biopsy small amounts of tissue for chemical markers indicative of plastic exposure. Plastics are known to absorb endocrine-disrupting chemicals and carcinogens from ocean water. In fact, plastics may concentrate toxins, such that they're found at levels up to 1 million times those found in the surrounding seawater.5

Such chemicals, which accumulate over decades, have been linked to health problems including altered growth, reduced fertility, and developmental and reproductive harm. "Marine filter feeders are likely to be at risk because they need to swallow hundreds to thousands of cubic meters of water daily to capture plankton," Germanov said.6

While it's unknown if consuming microplastics could prove lethal to a large filter-feeder, it's likely that they could cause "sub-lethal effects" that harm the animal's health nonetheless.7

Whales Could Be Swallowing Thousands of Microplastic Particles Daily

It's unknown just how much plastic sea animals are consuming, but it's estimated that fin whales swimming in the Mediterranean Sea may swallow 2,000 such particles every day.8

In 2016, researchers revealed high densities of microplastics in the Pelagos Sanctuary of the Mediterranean Sea, a protected marine area between Italy, France and the island of Sardinia. The area overlaps with whale feeding grounds and researchers found high concentrations of persistent, bioaccumulative and toxic chemicals in biopsies of Mediterranean whales.

" … [W]e believe 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," they noted.9 A previous case study of the Mediterranean fin whale revealed that more than half of plankton samples contained microplastic particles along with high concentrations of endocrine-disrupting chemicals called phthalates.

Further, blubber from stranded whales revealed that phthalates could act as a marker for the whales' intake of microplastics, which, at the time in 2012, was regarded as the first warning of microplastics' threat to baleen whales.10

Six years later, in 2018, research was published suggesting that the previous estimate of 5 trillion microplastic particles in the world's oceans was a major underestimate, with one area near the U.K.'s River Tame containing more than 500,000 microplastic particles per square meter alone.11 The silver lining to the study was that it revealed much of the microplastic pollution in the ocean may be coming from upstream in river catchments, so controlling these sources could help to curb the global problem.

As for how you can help to keep plastic of all kinds out of the ocean (and away from magnificent marine life like manta rays and whale sharks), avoid any products that contain microbeads, as well as single-use plastics like straws, bottles, bags, utensils and cups. By using less plastic personally, you can help keep plastics from entering the oceans and harming marine life.

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