Student Activities

Freeing the Elwha: "Marine-Derived Nutrients from Salmon"

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Grade Level:
Middle School: Sixth Grade through Eighth Grade


Through this activity, students will learn how the carcasses of dead adult salmon support young salmon and how salmon are essential to the marine food web as well as the freshwater ecosystems of the Pacific Northwest.

After completing the activity, students will be able to:

- Discuss the marine food web related to salmon.

- Understand the idea of algal blooms in the cold nutrient-rich waters of the North Pacific.

- Understand trophic levels, energy movement, bioaccumulation and biomagnification of nutrients and chemicals into top-level predators such as salmon.

- Understand the idea of these marine-derived nutrients entering the freshwater ecosystems and becoming the basis of the freshwater ecosystem food web. Freshwater ecosystems in the Pacific Northwest tend to be oligotrohic (containing few nutrients), so these marine-derived nutrients constitute an important influx that greatly increases the productivity of these rivers.

  • Shredder- Eat leaves and other vegetative particles and select those with fungi and bacteria attached to them for protein (includes mayfly and caddisfly larva).
  • Scraper/Grazers- Scrape biofilm, algae, and detritus from rocks, wood, and vegetation (includes snails and caddisfly larva)
  • Filter-feeder- Filter small particles out of the water-column, often dislodged by the shredders and scrapers (includes copepods, amphipods, blackfly and midge larva, hydra, etc.).
  • Collector-gatherer- Forage along the streambed for detritus, food particles, and fungi (includes stonefly larva and some mayfly larva).
  • Predator- An organism that hunts and feeds on other animals (includes dragonfly larva, water beetles, water striders, etc.)
  • Biofilm- A community of microorganisms living within a matrix of secreted materials secured to a solid structure such as river rocks or aquatic vegetation. They are often complex environments containing bacteria, algae, fungi, and protozoans.
  • Marine-derived nutrients (MDN)- Nutrients acquired by an anadromous fish and deposited in a freshwater or terrestrial ecosystem when that fish dies.
  • Oligotrophic- Containing few nutrients and therefore unable to support much life
  • Eutrophic- An ecosystem containing high levels of nutrients and therefore supporting high productivity. However, an overly eutrophic environment can result in algal blooms that cause the waters to become deficient in oxygen through the bacterial consumption of dying algae. These anoxic aquatic environments can then become dead zones to all but algae.
  • Nutrient cycle-Transfer of nutrientsfrom one part of an ecosystem to another.
  • Saprophyte- An organism, especially a fungus or bacterium, that grows on and derives its nourishment from dead or decaying organic matter.


Download Activity Instructions

Download Functional Feeding Groups Powerpoint

Download Marine-Derived Nutrient Cycling Powerpoint

Last updated: September 16, 2015