Ocean Pasturage

The two most important plants on earth are grass and diatoms. About grass the shepherd, farmer and scientist know a great deal. About diatoms and dinoflagellates, which are microscopic sea plants (phytoplankton), until the last 30 or 40 years even the scientist has known little. Last week in The Scientific Monthly Marine Biologist Winfred Emory Allen of University of California's Scripps Institution of Oceanography surveyed his recent researches on diatoms in the Pacific Ocean.

Diatoms are the grass of the waters--the major source of energy and sustenance for marine life. A few thousandths of an inch across, the diatom's jewel-like silica case encloses a drop of protoplasm. In it chlorophyll magically manufactures organic matter out of sunlight, carbon dioxide and water. As this photosynthesis proceeds, diatoms multiply by splitting. Though each diatom is invisible, they outweigh in volume and importance all other sea plants combined, including seaweeds which grow as big as oaks.

Most mature fish are carnivorous. Yet in the pyramid of life there must be more plant eaters than flesh eaters. Chief vegetarians of the oceans are copepods--tiny, flealike crustaceans related to lobsters and crabs. Copepods browse on the vast, undulating pastures of diatoms, converting plant life into animal life. Thereafter the cold, predatory struggle of the seas begins. On the copepods feed small fish like herring. On these feed larger fish like cod, as well as marine birds, seals, whales. Thus the importance of diatoms to man.

This floating ocean pasturage is forever changing. Where diatoms flourish one season, next season there may be few. Fish, birds, seals, whales follow the diatoms up and down the seas. When biologists have found the causes of the diatoms' mysterious shifts, they may be able to advise fishermen where the best catches can be netted, and how large future catches will be. Newly hatched fry often feed on diatoms before becoming carnivorous. Poor pasturage can mean survival of few fry, poor catches for fishermen.

Oceanographer Allen reports that in years of unusually warm Pacific water, diatoms were fewer. Diatoms flourish best in cold water, which contains more dissolved carbon dioxide than warm. Result is the well-known abundance of whales, seals, big fish in polar regions.

A single species of diatom, Allen found, rarely held the lead in one spot for more than ten days. The species vary greatly. Though all contain vital green chlorophyll, some diatoms and dinoflagellates are brown or yellow or red--whence the Red Sea. Other diatoms sometimes make the sea stink. In fact, diatoms probably cause the universal "fishy" taste and smell of sea creatures.

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