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What are red tides and other harmful algae blooms?

By Larry West, About.com

Question: What are red tides and other harmful algae blooms?
Answer: “Red tide” is the common name for what scientists now prefer to call “harmful algae blooms.”

Harmful algae blooms (HAB) are the sudden proliferation of one or more species of microscopic plants (algae or phytoplankton), which live in the ocean and produce neurotoxins that can cause negative and sometimes fatal effects in shellfish, fish, birds, marine mammals, and even humans.

There are approximately 85 species of aquatic plants that can cause harmful algae blooms. In high concentrations, some HAB species can turn the water a reddish color, which is why people started calling the phenomenon “red tide.” Other species may turn the water green, brown or purple while others, although highly toxic, will not discolor the water at all.

Most species of algae or phytoplankton are beneficial, not harmful. They are essential elements in the foundation of the global food chain. Without them, higher life forms, including humans, would not exist and could not survive.

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