SCIENCE

Marine biologists unravel baleen whales’ remarkable “manuring mechanism”—and secrets of the ocean food web. (NPR)

Let our resources fill you in on all you ever wanted to know about marine food webs but were afraid to ask.

Discussion Ideas

• Read the typically terrific article (with illustrations!) by one of my very, very favorite journalists, Bob Krulwich. Then, compare this photo of whale poop with this photo of whale poop. Which do you think came from a blue whale, and which from a killer whale? Why? Which variety of poop is the fertilizer that contributes to the marine food web?
  • Which is which? The bright pink poop came from a healthy blue whale.
  • How do I know this? You are what you eat, and the blue whale poop shows that their diet is mostly krill—tiny, shrimp-like (and pinkish) crustaceans.
  • Which is the ocean fertilizer? The iron-rich blue whale poop is the ocean fertilizer, contributing to blooms of phytoplankton—the primary producers in the marine food web. When whales poop near the ocean surface (where there is plenty of sunlight for photosynthesis), “that extra iron would create blooms of phytoplankton, which would then be eaten by krill, leading to a boost in the krill population, leading to … yes … bigger whale dinners!”

• Read through our activity “Marine Food Chains and Biodiversity.” Adapt its questions to relate to the NPR whale poop article.
  • What are the producers in the marine food web?
    • phytoplankton (algae) 
  • What are the primary consumers?
    • krill
  • What are the secondary consumers?
    • baleen whales (specifically, blues and humpbacks)
  • What environmental and chemical conditions are necessary for a healthy marine food web?
    • Nutrients and sunlight need to be present for phytoplankton to bloom and produce energy through photosynthesis.
  • Bonus: My favorite part of the article outlines another, more complex marine food web—the deep-sea ecosystem, 914 kilometers (3,000) feet below the surface. Here, the primary consumers of plankton are fish and squid. The secondary consumers are giant squid. Sperm whales, diving deep to hunt iron-rich giant squid, are apex predators in this ecosystem. “Pressed by the weight of the ocean, their digestion stops; they don’t excrete [poop]. They consume the iron below, hold it in, climb back to the surface, and that’s where they poop. Every sperm whale, it is said, draws 50 tons of iron to the surface every year.”

• Read through our activity “Ecological Relationships.” Adapt its questions to relate to the NPR whale poop article.
  • What ecological interactions are present in the marine food web (as outlined in the NPR article)?
    • predation—whales are predators of krill
    • symbiosis—whales and phytoplankton have a close ecological relationship, just one degree (krill) of separation in the food web
    • mutualism—both whales and phytoplankton benefit from the whales’ pooping behavior (although the plankton are ultimately consumed)

• Check out Krulwich’s food pyramid, and compare it to the two marine pyramids in our activity “Marine Food Webs.” Which one does it most resemble?
  • Krulwich is a pretty smart guy and did a good approximation of the more sophisticated example, the ecological pyramid, which displays how biomass is distributed.

• Read through our activity “Create an Imaginary Marine Ecosystem,” and compare its sketches of marine food webs with the illustration at the end of the NPR article. Did Krulwich do a pretty good job? Are the food web’s biotic and abiotic factors represented? Are the ecological relationships represented?
  • Of course he did a good job!
    • The abiotic factors are are sunshine and whale poop (and other nutrients). The biotic factors are phytoplankton, krill, and, of course, the big beautiful whale.
    • The ecological relationships are clearly represented by arrows, making this a pretty simple food chain that is part of a larger food web. The larger food web probably includes other consumers, such as sharks, seals, and penguins.