Plankton: basic to marine life food chain

Published: Thursday, October 24, 2013 at 10:18 AM.

By Tom Baird


As the weather cools, the waters of the bay and Gulf will become clearer. This isn’t so much from a lack of suspended sediment, but from fewer microscopic life forms adrift in the water column. There exists in the oceans of the world, in bays, lakes, and in nearly every other natural body of water, a population of organisms so immense that it defies counting. Everyone while swimming has brushed up against millions of these creatures without being aware of their presence. No doubt you swallowed a large number while learning to swim.

Although limited studies of this population were made before 1887, it was not until that year that oceanographer Victor Hensen first proposed a name for this vast assemblage…plankton. The term refers to those plants and animals, mostly, but not entirely, microscopic in size, that are made “to wander or drift,” under the influence of ocean currents. The same root word gives us the name planet, because to early astronomers the planets seemed to wander against the more fixed background of the distant stars.

Although most planktonic organisms have the ability to swim, their efforts are too feeble in the presence of oceanic water movements. One definition of plankton is the inability to swim faster than one knot. Because of their vast numbers, wide distribution and beneficial biologic activities, plankton are considered the most important inhabitants of the marine world, with all forms of life directly or indirectly dependent on them.

Planktonic creatures are basic to the food chains of all marine life. Sponges, tube worms, scallops, clams, oysters and sea squirts are just some of the animals that filter sea water to gather them. Herring fisheries use plankton indicators to predict potential catch. Giant baleen whales, over 100 feet in length and reaching fantastic weights of 150 tons, feed almost exclusively on plankton. Diatoms, one type of plant plankton, are a major source of vital oxygen in the atmosphere and for proteins that animal life cannot synthesize but require. Without plankton the seas would be a wet desert.

Not all planktonic creatures are microscopic. Jellyfish, as large as cannon balls, are moved about the oceans by currents. Comb jellies (Ctenophora), depending on the species can range from the size of a hickory nut to 4 – 6 inches. Many plankters are visible to the naked eye. Copepods (crustaceans) are the insects of the sea, and are about the size of a lower case o on this page. They are the most abundant and universally distributed animals in the plankton.

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