Glen Gullikson, age 12, of Rockford, I11., for his question:

What is plankton?

Plankton is a sort of seafood salad, often too fine for our eyes to see. Yet it rates as the most important thing in all the ocean. In one way or another, every sea dweller depends upon plankton to stay alive. For some it is their only food. Those that do not eat plankton feed upon the animals that do eat it. This is much like the grass and green stuff on the dry land, Most land animals live on plant life.

Those that do not, live on the plant eaters. Chances are, there is a little plankton in every pail of sea water, If you dip in with a fine net and let t he water run out,, the plankton will stay behind as a green scum. Actually, that green scum is a. world of tiny living things, both plants and animals.

There will be a countless variety of algae plants, little one celled seaweeds. There will be jewel like diatoms in a million different shapes, each one more beautiful than the next. There may be fish eggs and larvae, tiny sea worms and sea crustaceans. A few of these midgets may be just big enough for your eyes t o see. You will need a microscope to study the smaller ones.

The plankton salad begins with microscopic plant life aril even ocean plant life changes with the seasons. In the cold winter seas, the vital minerals tend to be dissolved in waters below the surface. The tiny plant life must remain near the surface sunlight and hence endure short rations of the chemicals needed for growth. Come spring, the surface water sinks and warm, mineral rich water wells up from below. The plant life bursts into activity. Vast areas of the ocean are then tinted red, brown or green with teeming algae,

Spring too is the time when larger creatures multiply. Fish eggs float to the surface in countless billions. Glassy worms and newly hatched larvae add themselves to the lush plankton meadows. Baby shrimps, the wriggly larvae of the barnacles and the oysters join in the feast, and all this rich plankton is the start of a great food chain.

Herring, mackerel and countless larger fish come in to feed on the little fellas feeding on the plankton. The tunas, the hungry sharks and the squids come in to feed on the herrings and their allies.

The biggest animal on earth., the blue balleen whale, eats nothing but plankton all his life. He follows where the plankton is richest throughout the world wide oceans. Time after time he opens his great mouth and takes in a roomful of water. He closes his mouth, forces up his tongue and sieves the water out again through his curtains of whalebone balleen. The plankton stays behind to be swallowed.