Initial Publication Date: August 5, 2005

Bring 'em Back Alive - Plankton Nets

Created by Lorraine Olendzenski, St Lawrence University

Plankton refers to organisms that spend all or some of their lives living at the water surface. Viruses, bacteria, protists, fungi, and animals ranging in size from nanometers to several centimeters can all be found in the plankton of fresh or marine waters. An easy way to sample planktonic organisms is with a variety of inexpensive, easy to assemble nets. There are many ways to make a plankton net (e.g. see Microcosmos Curriculum Guide, Kendall Hunt Publishers). Here is a variation that we will try.

Materials Needed

Nylon stocking or knee high hose
Strong Twine
Thin Rope (e.g. clothesline)
Duct tape
Small can (e.g. tuna can, coffee can, cat food can) or strong plastic cup that can be cut with a razor blade
Lightweight jar (e.g. spice bottle) or disposable plastic test tube (50 ml size)
Strong rubber band

Procedure

Find a can small enough to fit inside the rim of the nylon stocking or knee hose being used. Cut off both ends of the can with a can opener (or cut off the bottom end of the plastic cup). Make sure edges are smooth. Put the stocking through the can and fold the edge of the stocking over the outside rim.
Take three equal lengths of string, approximately 12 inches long, gather in a bundle and tie with a single knot at one end. Spread the three pieces over the top of the can so they are equidistant from each other and hang below the folded edge of the stocking. The knot should be above the center of the can opening.
Tightly wrap duct tape all around the can so that the strings and stocking are held securely in place. Enough string should hang below the bottom edge of the duct tape so that each can be flipped up and tied to itself with a small knot at the top of the duct tape.
Drop an uncovered, 50 ml plastic test tube into the toe of the stocking. Secure this in place with a rubber band or tightly tied piece of string.
A long tow rope (clothesline at least one yard long) can be attached to the knot holding the three strings together at the top center of the plankton net.

Helpful Tips

This net can be used to sample the surface of the water, simply by slowly pulling it along the top of the water, or it can be dropped to a certain depth in the water (from a pier or boat for example) and dragged vertically upward to sample the water column.
As water washes through the stocking, organisms will be caught in the mesh and washed down into the bottom tube. To insure that all organisms are washed off the sides of the net, a squirt bottle full of water from the environment can be used to wash organisms into the bottom test tube.
To transport organisms back to the lab, empty the concentrated sample from the test tube into a slightly larger jar, add water from the environment sampled, and cover. The temperature of the sample should not be allowed to change very much. Covered jars can be kept in a large bucket and covered with water from the environment to keep the temperature from changing too much.
Samples can be observed under a dissecting scope, or pipetted onto a microscope slide and observed under high power.