Bring 'em Back Alive - Styrofoam Traps

Created by Lorraine Olendzenski, St Lawrence University

The tiny spaces in Styrofoam peanuts and blocks of polyurethane foam can be colonized by microorganisms and can be used to fish bacteria and protists out of marine and freshwater environments.

Materials Needed

  • Several pieces of string or monofilament fishing line (approx. 8 inches each)
  • Fishing weight
  • Styrofoam peanuts or polyurethane foam
  • Leading String
  • Covered jar or Ziploc bag
  • Petri dishes


  1. Gather several pieces of string or monofilament fishing line (approximately 8 inches long) together in a bundle and tie in a single knot at one end. To the end of each piece of string except one, tie a Styrofoam peanut or small piece of soft foam. Add a fishing weight to the last piece of string and add a long string or fishing line leader to the top of the tied bundle. This array of traps can be tied to a pole and suspended in the water, or tied to a stone or brick and allowed to sink to the bottom of the water being sampled. Be sure that the foam is not exposed at low tide. The length of string leading to each foam piece should be short so that the foam does not float above the water surface.
  2. As with coverslip traps, the longer they are allowed to sit, the more different organisms will be observed. Allow traps to sit at least 24 hours before removing. Collect traps in the water that are suspended in and place into a Ziploc bag or covered jar. To observe organisms, simply squeeze the Styrofoam or polyurethane foam pieces into a dish. Observe dishes with a dissecting scope or pipette a drop of water onto a microscope slide and cover with a coverslip to observe under the light microscope.


Download (Microsoft Word 20kB Jun13 05) this activity in the form of a Word document.