Plankton — the pastures of the sea

   One of the most important and far-flung kinds of life in the sea is plankton. It is not a single kind
of life but a floating community of both plants and animals, found in surface waters. Most are tiny, even microscopic. There are diatoms and other one-celled plants, and slightly larger ani­mals that feed on the plants and spend all their lives floating on the waters.
   Thousands upon thousands of different species—various larvae, minute shelled animals, sea worms and sea "spiders," baby fish, and others— make up a plankton community. None of these creatures can swim against the currents. They simply drift.
   Plankton is the basic food supply of the sea. For in the sea, as on land, animals depend on plants for food. Only the plants can change simple substances into the sugars, starches, and proteins that nourish animals. So the tiniest ani­mals feed on the diatoms, which make up six tenths of plankton. And larger animals feed on the smaller.