Red Tide Updates
What is a Florida red tide?
A red tide is a higher-than-normal concentration of
a microscopic alga (plant-like organisms). In Florida, the species
that causes most red tides is Karenia brevis. This organism produces
a toxin that can affect the central nervous system of fish. At high
concentrations (called a bloom), the organisms may discolor the water.
However, red tides are not always red. They can appear greenish, brownish,
and even purple in color. The water can even remain its normal color
during a bloom.
Is red tide a new phenomenon?
No, it is not a new phenomenon. Red tides have been
documented along Florida's gulf coast since the 1840s and probably
occurred much earlier. Fish kills around Tampa Bay were mentioned in
the logs of Spanish explorers.
Can red tides be predicted?
Currently, red tides can’t be predicted, but researchers are investigating
the possibility. The effects of a red tide (e.g., dead fish and respiratory
irritation in people) depend on the location and concentration of the
red tide microorganism at a given time. The effects also depend on wind
speed and direction. It is important to realize that many people still
enjoy the beaches during red tides. Respiratory irritation and dead fish
are not always present.
Do red tides occur anywhere else?
Yes, red tide organisms occur elsewhere. Although the
organism that causes Florida's red tide is found almost exclusively
in the Gulf of Mexico, blooms have been found off the east coast of
Florida, and a bloom was detected off the coast of North Carolina in
1987. Scientists believe the Florida Current and Gulf Stream Current
carried K. brevis out of the Gulf of Mexico, around South Florida,
and up to the Carolina coast. Other types of microorganisms cause different
kinds of red tides (now called harmful algal blooms) in other parts
of the world as well.
How is red tide related to respiratory irritation?
People experience respiratory irritation (coughing,
sneezing, and tearing) when the red tide organism (K. brevis) is present
along a coast and winds blow its toxic aerosol onshore.
CAUTION: People with severe or chronic respiratory conditions (such
as emphysema or asthma) are advised to avoid red tide areas. Generally,
symptoms are temporary. Once exposure is discontinued, symptoms usually
disappear within hours.
Is it safe to swim during a red tide?
Yes, swimming is safe for most people. However, red
tide can cause some people to suffer from skin irritation and burning
eyes. Use common sense. If you are particularly susceptible to irritation
from plant products, avoid red tide water. If you experience irritation,
get out of the water and thoroughly wash. Do not swim among dead fish
because they can be associated with harmful bacteria.
Does cooking destroy the red tide toxin?
No, cooking does not destroy the red tide toxin.
Is it okay to eat shellfish during a red tide?
No, shellfish should not be eaten during a red tide.
If a shellfish-harvesting ban is in effect, it is not safe to eat mollusks
(e.g. clams and oysters). However, edible parts of other animals commonly
called shellfish (e.g. crabs, shrimp, and lobsters) are not affected
by the red tide organism and can be eaten.
Which shellfish are included in a shellfish-harvesting ban?
Harvesting of bivalve mollusks such as clams, oysters,
and coquinas is banned during red tides.
Is it okay to eat fish, crabs, or shrimp during a red tide?
Yes, fish, crabs, and shrimp can be eaten during a
red tide because the toxin is not absorbed in the edible tissues of
these animals. However, if a red tide is in the area, eating distressed
or dead animals is discouraged because the reason for the animal’s
strange behavior or death cannot be absolutely known. It could be something
unrelated to red tide.
Is it okay to eat scallops during a red tide?
Yes, as long as you only eat the muscle of the scallop.
Do not eat whole animals.
Where can I find more information about red tides?
Visit the Harmful
Algal Bloom Section for more information.