|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
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
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.
All information courtesy Florida Marine Research Institute
To learn more visit the Florida Marine Research Institute website: www.floridamarine.org