Susan Barr, age 14, of Philadelphia, for her question:
Why is plankton so important?
Ecologists mention plankton when they warn us about the pollution of ocean waters. This almost invisible stuff happens to be the super supermarket of every creature that lives in the sea. As if this is not enough to make it important, it also provides the major part of the oxygen used by all the creatures that inhabit the land. No wonder ecologists get worried when the world's plankton supplies are threatened. Everybody should worry about it.
A cup of seawater is loaded with dissolved chemicals and usually contains a few floating fragments. Perhaps it is tinged very slightly with green. You may not suspect it, but this cup of salty seawater contains a sample of plankton. Chances are, it teems with an assortment of living things, too small to be seen without a microscope. The green tinge, for example, is added by microscopic algae. In astronomical numbers, these humble little members of the plant world provide oxygen for marine animals. They also pour a surplus into the air to be wafted over the land.
Actually, our cup of seawater was a rather poor sample of plankton. We could get a richer sample in the Antarctic or in some other region where the water is thronged with assorted fishes. If we sift a scoop of this water through a fine net, we are left with a layer of slime and a few fragments that look like tiny creatures. The microscope proves these fine fragments to be an assortment of eggs and larvae, a few of which will survive to become fishes, crabs and other larger animals. of the sea. The slime turns out to be an assortment of microscopic plants and animals.
These midgets float near the surface of the seas in astronomical numbers. The miniature plant cells use sunlight to make their food and release oxygen into the air and water. The miniature animals feed on the plants and on each other. Together they make a highly nourishing seafood salad of meat and vegetables. Shrimps and dozens of other small swimmers feed upon it. The great blue whale is theearth's largest animal. He uses the balleen curtains in his mouth to sift plankton from the water. This is his only food.
Most other sea dwellers do not feed directly on plankton. But without it they would starve. This is because the floating seafood salad is the base of their food chain. The smaller marine animals thrive on it, multiply and provide food for the larger ones. These provide food for bigger and still bigger fishes. For example, half a ton of plankton feeds 100 pounds of small shrimp who feed ten pounds of mackerel. There is not much of this basic seafood salad in a cup of ocean water. But the vast oceans have enough of it for all their creatures.
As usual, this vital food chain is a delicately balanced pyramid. When offshore waters are polluted by human and industrial wastes, some species in the plankton are destroyed and others multiply beyond bounds, adding more pollution to the water. The basic balanced diet is upset and many fishes that depend on it must perish. Some of them may be valuable as human food.