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National Aquatic Resource Surveys

Indicators: Phytoplankton

What are phytoplankton?

Phytoplankton are free-floating, microscopic algae that inhabit the sunlit, upper layer of most freshwater and marine environments. They are usually responsible for the color and clarity of lakes, wetlands, rivers, streams and estuaries.

Why is it important to evaluate phytoplankton?

The ability of phytoplankton to photosynthesize (i.e., to use the sun’s energy to turn carbon dioxide and water into food and energy) makes them a primary source of energy in most aquatic ecosystems, providing the food source for higher order organisms such as zooplankton and small fishes.

What can phytoplankton tell us about the condition of water?

Phytoplankton are uniquely adapted to the specific depths, habitats, nutrients, and chemical conditions in which they reside. Information on the relative diversity and taxonomic richness of the phytoplankton community can be used as an indicator of the biological condition of a site.