2005-1-31
I'm Phoebe Zimmermann with the VOA Special English Agriculture
Report.
Different events can change the balance of sea life. Red tides
are an example. These can happen in oceans, rivers or lakes anywhere
in the world. What happens is that algae suddenly increase in
numbers. Algae are single-celled organisms. They are a normal part
of sea life.
As they spread, or bloom, the water may turn red or brown.
Sometimes the water does not change color at all. But deadly algae
could still be present.
Some kinds of algae produce a strong poison. This can build up in
shellfish that eat the algae and make them poisonous, but not kill
them. Other kinds of algae may kill sea life by reducing oxygen
levels in the water. In some red tides, thousands of dead fish
appear on beaches.
Scientists do not know exactly why red tides happen. But they say
a combination of conditions all play a part. These include water
temperature, nutrients in the water and water flow. Pollution could
also play a part.
A number of different algae can cause red tides. A common form
has the scientific name Karenia brevis. It is often linked with red
tides in the Gulf of Mexico and the Caribbean area.
Algae poisons build up in the tissue of shellfish like clams,
oysters and mussels. This makes them unsafe for several weeks after
a red tide goes away.
People are also advised not to eat the organs of fish or
shellfish like shrimp, crab or lobster. Scientist Richard Pierce
says the poison produced by K. brevis does enter the meat of these
creatures. But he adds that there have been no reports of people
getting sick from eating healthy fish during such a red tide. Mister
Pierce is director of the Center for Eco-toxicology at the Mote
Marine Laboratory in Florida.
There are different kinds of shellfish poisoning, some more
severe than others. Effects can include diarrhea, fever, stomach and
muscle pain, and breathing problems. In severe cases people can die
unless they receive treatment.
Experts say older people are especially likely to experience
severe effects from algae poisons.
Some people who swim during a red tide report skin problems or
shortness of breath. Scientists have more to learn about the
possible risks of swimming in red tides or breathing algae poisons
in the air.
This VOA Special English Agriculture Report was written by Mario
Ritter. I'm Phoebe Zimmermann.