Sheila Jones, age 15, of Montgomery, Ala., for her question:
WHAT CAUSES RED TIDES AT CERTAIN SEASONS?
A so called red tide or red sea may bring disaster to a beach, a river or a lake. It is caused by a population explosion among certain minuscule creatures that live in the water. Scientists are not sure when or why this happens, so the event is hard to predict.
Population explosions are disastrous because they upset the ecology, or balance of,nature. Normally, things are arranged so that a multitude of assorted plants and animals can share a given area on a basis of give and take. This harmonious existence requires enough and no more of each species. When one species multiplies out of its proper proportion, others are starved or suffocated.
A so called red tide occurs when certain microscopic dinoflagellates go on a multiplication spree. Nobody knows for sure, but this may occur when these single cell creatures are supplied with extra food, minerals or suitable temperatures. Normally there may be 1,000 of them in a quart of the local water. Suddenly there are enough of them to color the water red or rusty brown.
A red tide of this sort may be fairly harmless and even provide extra food for larger water dwellers. But a few of the exploding dinoflagellate types can be disastrous. Some give off poisonous chemicals in large enough quantities to destroy the local fish populations.
Dead and decaying fishes wash up on the beach or lake side, adding horrible odors to the air. Other dinoflagellates give off milder poisons that kill indirectly. They poison shellfish which poison other creatures who eat them. Sometimes the local sea life is not destroyed by poisons. The population explosion consumes more than its share of oxygen, and other water dwellers die from suffocation.
Red tides occur most often off our southern shores. No one knows when or where they will strike. They may be limited to a small stream or contaminate several square miles of ocean water. They may last merely a few hours, a week or as long as several months.