ENVIRONMENT

Tiny pieces of plastics are turning up in the feces of seals that feed on whole fish, demonstrating how seaborne contamination can move up the food chain. (Seeker)

Use our inquiry-based activity to help guide student discussion about human impact on ocean animals.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• New research documents the presence of microplastics in the feces of grey seals. What are microplastics?
  • Microplastics are just what they sound like: tiny pieces of plastic, usually defined as between .3 and 5 millimeters (0.01 to 0.20 inches) in diameter—no thicker than a grain of rice. The microplastics discovered in the seal poop were fibers and fragments about 1.5 millimeters (.6 inch) in diameter.
    • Some microplastics have broken off from larger pieces of plastic debris, such as fishing gear and packaging.
    • Other microplastics, so-called “nurdles” are pellets used to make plastic products.
    • Learn more about plastic ocean debris with our reference resource.

 

• The grey seals tested in the research are captive, residents of an outdoor enclosure at the Cornish Seal Sanctuary in southwestern England. Their habitat and diets are entirely determined by human caretakers. The caretakers did not feed the seals plastic. So how did plastics end up in their poop?
  • Trophic transfer in the food chain. Grey seals are apex predators in their ecosystem. Seals feed on mackerel (fish), and fish feed on plankton.
    • Microplastics can be traced through every trophic level, through a process called “trophic transfer.” Download our diagram of a marine food pyramid for some help with trophic levels. Follow the plastic:
      • producers: Microplastics are tiny enough to blend in with primary producers such as phytoplankton and first-order consumers such as zooplankton. Zooplankton may also accidentally consume microplastics when feeding on phytoplankton, seagrass, or algae.
      • consumers: Wild Atlantic mackerel are exposed to microplastics when feeding on zooplankton, their main food source. Mackerel feed by approaching a plankton swarm and opening their mouths as wide as possible, consuming millions of copepods, krill … and microplastics. (The authors call this an “indiscriminate feeding strategy.”) Mackerel may also consume microplastics indirectly, if the plankton has already consumed the plastic itself.
      • apex predators: The grey seals at the sanctuary are fed whole Atlantic mackerel, an abundant species of fish in the Celtic Sea and English Channel, the two bodies of water that bracket the South West Peninsula. Wild grey seals regularly prey on mackerel.

 

• The seals pooped out the pollution—their digestive system successfully excreted the waste material. They were not directly harmed by it. So what’s the problem?
  • The lead researcher reminds us that “even if animals eventually pass the plastic, long-lived toxins can latch onto the particles and enter the body.” This bioaccumulation is what concerns scientists studying not only seals, but other carnivorous mammals. Like humans. “‘Persistent chemicals, such as PCBs, are known to adhere to the surface of microplastics. They can cause endocrine disruption and alterations to immune system function if ingested.’ Those chemicals ‘are more of a concern than the particles themselves.’”

 

TEACHERS TOOLKIT

Seeker: Seal Feces Reveals Microplastics Are Traveling Up the Food Chain

Nat Geo: How People Affect Ocean Animals and Plants activity

Nat Geo: Marine Food Pyramid illustration

(extra credit!) Environmental Pollution: Investigating microplastic trophic transfer in marine top predators