HANDS-ON ACTIVITY


MAKE A PLANKTON NET

A plankton net is a device for concentrating small marine organisms for closer examination. The small organisms collected in a plankton tow will be plants and animals that go unnoticed by most people. A microscope is needed to identify many of these organisms, but you see can see some of the larger zooplankton with your naked eye, and even better with a magnifying glass.

A net with very fine mesh is used in the plankton net because many of these timy organisms would pass through an ordinary dip net. The plankton net is essentially a cloth funnel that allows water to pass through, but retains the living organisms. The collected organisms will be found in the small glass or plastic bottle found at the bottom of the net.

Materials

One leg of nylon stockings
A wire coat hanger
Rubber band
String
Small flask or bottle (film canister, pill bottle, baby food jar)
Duct tape

Making the net

Uncoil the coat hanger, then form it into a circle. Bring the wider end of the stocking leg through the circle and fold it back over the wire. Sew or tape the stocking in place. Cut the toe out of the other end of the panty hose. Slide the end over the mouth of the bottle or jar. Wrap the rubber band tightly around the stocking end and the mouth of the jar. Use the string to make a "bridle" to pull the net with.

It should look like this when you're done:

Using the net

Find a place where the water is calm and shallow enough for you to wade. It should be deep enough, though, that the net does not drag on the bottom. Walk back and forth through the water, pulling the net behind you. You should keep the mouth of the net just below the surface. The longer you tow the net, the more you'll catch. Try towing for 15 minutes or more.

It also works well to tow the net from a boat, but you must go very slowly or else you'll rip the net.


Looking at your plankton

Remove the jar or bottle from the bottom of your net and pour the contents into a larger jar (such as a peanut butter jar) of seawater. Rinse the bottom of the net in the larger jar, too. You can probably see a few copepods and crab larvae if you look carefully.

You can keep the plankton alive for about 24 hours in the refrigerator. If you would like to preserve your sample, fill the jar with enough rubbing alcohol (from the drugstore) that you have half alcohol and half sea water.

Unless you have access to a strong microscope, you will not be able to see phytoplankton. But you will be able to see some zooplankton with your naked eye and with a magnifying glass. See if you can identify some of them.