Zooplankton are a diverse group of animals (usually tiny), that drift in aquatic environments. Several aquatic animals live out their life as part of the zooplankton (such as copepods and amphipods), while the egg and larval stages of some animals (such as crabs, clams and some fish species) are part of the zooplankton only until they grow large enough to start their adult life on the sea floor or other habitats.

Zooplankton are also an important first tier of the food chain. These drifters are vulnerable to changing ocean conditions such as temperature, salinity, pH, and other factors. SEM is a critical tool for scientists currently studying the biological effects of ocean acidification on calcium carbonate structures in organisms, such as geoducks and krill. Acidic seawater can reduce the amount of carbonate minerals needed by these animals to form their shells. These deleterious effects may ripple up the marine food chain to endangered salmon that depend on zooplankton for their survival as well as orcas that depend on salmon.

  • Amphipod


    Amphipods are small crustaceans. Some live on the beach, others burrow into sand or mud. This amphipod is one of many species that lives in the water as part of the zooplankton.

  • Two week-old Geoduck

    Two week-old Geoduck

    Newly hatched clams (and snails) look different than the adults, they have tiny cilia that allow them to swim as part of the zooplankton. This two week-old geoduck has just lost its cilia. It will sink to the sea floor and soon begin to develop the shell shape and long neck typical of adult geoducks. Ocean acidification can dissolve some of the calcium in the shells of young clams and snails.

  • Young surfsmelt eating a baby crab

    Young surfsmelt eating a baby crab

    This four month-old surf smelt (Hypomesus pretiosus) was raised in the laboratory and was feeding on zooplankton. This surf smelt tried to swallow a baby crab (zoea). Baby crabs or zoea do not resemble adult crabs; they have long spines, one of which can be seen protruding through a hole above the smelt’s upper lip. Surf smelt spawn on gravel beaches in Puget Sound and other Pacific Coast areas. Eggs that are spawned in urban areas are vulnerable to habitat loss and pollution.