Don: It's time once again for the A Moment of Science^® mailbag...

Yaël: A listener writes:

     Dear A Moment of Science,

     I know that red tides have something to do with the ocean turning red near beaches,      but I'm not sure what this means or why it's important. So what is a red tide?

D: Wasn't "Red Tide" a movie about a submarine or something?

Y: That was "Crimson Tide." A red tide is when lots of algae bloom near the shoreline      and make the water appear discolored. But "red tide" isn't the best name, since the      water doesn't always look red--sometimes it appears green, brown, or reddish-      orange.

D: Okay -- so why is this interesting?

Y: Well, for one thing, red tides are sometimes toxic. They've been known to kill fish,      shell fish and marine mammals like manatees. A really potent red tide can even harm      people who breathe in the toxic gasses it gives off, or who eat poisoned shellfish.

D: Wow. What makes it so toxic? The algae?

Y: No--the algae is fine . . . it's microorganisms that feed on the algae--called      dinoflagellates--that are the problem. They produce these complex, poisonous      compounds that kill off sea life. Scientists are still trying to figure out exactly how and      why this happens.

D: So is there anything scientists can do to stop red tides?

Y: No, at least not yet. But the more scientists learn about how red tides happen, the      better they'll become at predicting when and where red tides might occur.  

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