RED TIDE …...
MORE THAN MEETS THE EYES AND NOSE
On a sultry Fall morning
of 1947, the community of
Red tides occur throughout the world, drastically
affecting Scandinavian and Japanese fisheries, Caribbean and South Pacific reef
fishes, and shell fishing along
Florida red tide blooms typically begin in the
Gulf of Mexico 40-80 miles offshore and move slowly southeast with the
prevailing ocean currents toward the Tampa Bay area. As the bloom progresses,
the density of red tide organisms increase to several million cells in each
liter of sea water, and the effected area expands to
many square miles. The result is a mass of deadly toxin containing water
sweeping toward the southwest
As the bloom approaches the shoreline, we begin to
see and feel the obvious effects: dead fish, the characteristic burning
sensation of the eyes and nose, and dry, choking cough. When the bloom is
severe, fish die rapidly from the neurotoxic effects
of the red tide which enter their bloodstream through the gills. Because the
fish die so quickly, these toxins do not have time to build up in their tissue.
Fish exposed to lower (sub lethal) concentrations, however, may accumulate
these toxins in their body. New evidence from current research suggests that
such bioaccumulation in fish eaten by dolphins may have been a major factor in
the deaths of more than 700 of these marine mammals in 1987.
Red tide populations well below the fish kill
level pose a serious problem for public heath through shellfish contamination.
Bivalve shellfish, especially oysters, clams and coquinas,
can accumulate so much toxin that they become toxic to humans. Public health concerns also emerge from studies that show the
presence of airborne toxins have an impact on the human respiratory system.
Because of the severe economic and
public health effects of red tides, much consideration has been given to
controlling the blooms. Control is only feasible within confined areas, such as
fish hatcheries and aquaculture ponds, and research is underway to assess
various control methods. Control in the broad expanses of the
Historical evidence indicates that red tides have occurred along the
The more we learn about red tide, the more
intriguing this natural phenomenon appears. There is much more to this than is
detected by our eyes and nose. The red tide organism plays a very important
role in the conversion of solar energy to chemical energy (photosynthesis), a
process essential to the survival of all animals. Why this little menace also
produces neurotoxin is still a mystery. Mote is dedicated to research that will
help us, not only understand the natural and man made factors that influence
red tide, but also to minimize and mitigate the health effects to humans and
marine life.
image courtesy of Kat
THE FACTS:
WHAT IS RED TIDE? Red tide is the result of a massive multiplication (or
"bloom") of tiny, single celled algae called Karenia
brevis, usually found in warm saltwater, but
which can exist a lower temperatures. It is a natural phenomenon, apparently
unrelated to manmade pollution. In high concentrations, K. brevis may create a brownish red sheen on the surface
of the water; in other instances, it may look yellow green, or may not be
visible at all. Some red tides have covered up to several hundred square miles
of water. No one can predict when or where red tides will appear or how long
they will last since they are affected by many variables such as weather and
currents.
WHERE DOES IT COME FROM? K. brevis blooms are
initiated miles offshore of the
HOW DOES IT AFFECT HUMANS? Irritations of the eyes, nose, throat, tingling lips and
tongue are common symptoms that often occur during red tides. Waves, wind and
boat propellers in high concentrations of red tides disperse toxin particles
into the air causing these problems for people along the shoreline. People
suffering from severe or chronic respiratory conditions such as emphysema or
asthma, should try to avoid red tide areas. Symptoms usually disappear within
24 hours once the exposure is discontinued.
HOW DOES IT AFFECT MARINE LIFE? K. brevis produces potent
neurotoxins. Filter feeding shellfish, such as oysters, clams, mussels and
other bivalve mollusks, that consume K. brevis
concentrate the toxin in various organs. Whereas red tide toxins are deadly to
fin fish, shellfish are unaffected. These toxins also are incorporated into the
marine aerosol, which causes the respiratory irritation to people along the
shore.
What's
Safe? What's Not?
Shrimp, Crab, Scallops and Lobsters in red tides are SAFE to harvest and eat, since
these shellfish do not accumulate the red tide toxin in the meaty or hard
muscle tissue which we normally consume. It is NOT a good idea to eat
liver, organs, or other soft tissue of shellfish.
The muscle or "hard" meat of
freshly caught fin fish in red tides are SAFE to eat provided the
fish behave normally. Although no evidence of harmful effects in humans from
contaminated fish have been reported, it is NOT a good idea to eat
liver, organs or other soft tissues.
Oysters, Clams, Mussels, Mollusks, Whelks
are UNSAFE to harvest & eat since they may accumulate red tide
toxins in their tissues. This remains effective until the Department of
Environmental Protection determines that the waters are clear of red tide &
shellfish are free of red tide toxins, which may take several weeks after a red
tide bloom is over.
Swimming & Enjoying the Gulf Beaches
are fine for most people; however, some people have reported skin irritation
after swimming. However, respiratory irritation and fish kill are not always
present during red tide outbreaks. Use common sense -- if the red tide bothers
you, avoid the area.
Sarasota
County Health Department: (941) 954-2900
Mote
Marine Laboratory: (941) 388-4441