Plankton Tow, Introduction to Food Webs and Phytoplankton


Maine Lakes Society and Lakes Alive!



Plankton isn’t just a character from ‘Spongebob’; it’s actually a real life aquatic organism called a cyclops and it’s just one of many microscopic floating animals called zooplankton that live right here in our lakes. To catch them, we use a fine mesh sieve called a plankton net and drop it off the bow of the Melinda Ann at a specific depth. Zooplankton (microscopic floating animals) is caught in the mesh while phytoplankton (microscopic floating plants) does not, because they are typically smaller and pass straight through it. The contents of the sieve are brought aboard and identified using Melinda Ann’s Ken-a-Vision microscope projector.


Essential Question

  • Does this lake support zooplankton?
  • Since zooplankton eats phytoplankton, what can you assume from the presence of zooplankton?
  • How many species of zooplankton could you identify from the plankton tow?
  • Which of these critters is your favorite?

Learning Objectives

  • To capture and examine zooplankton, the microscopic animal plankton that feed on phytoplankton found near the surface during the day.  Phytoplankton is found near the surface because these tiny plants need sunlight to grow.
  • Plankton is the basic part of the food web that supports frogs, fish, turtles, birds and other aquatic animals.
  • The amount of zooplankton in a lake depends on the availability of phytoplankton.


Additional Info
Video and presentation of a plankton tow in Lake Superior
Standard method for a vertical plankton tow
Photos of common lake zooplankton
Pictorial guide to freshwater algae
Great Lakes Water Life Photo Gallery: Algae
Pictorial Guide to Common Phytoplankton of Lake Champlain and the Lower Great Lakes


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