RED TIDE FACT SHEET
What is Red
Tide?
 Red Tide is caused by a "population explosion" of toxic,
naturally occurring microscopic plankton (specifically, a subgroup known as
dinoflagellates). Explosions or "blooms" are coastal phenomena caused be
environmental conditions which promote explosive growth. Factors which are
especially favorable include warm surface temperatures, high nutrient content,
low salinity and calm seas. Rainy followed by sunny weather in the summer months
is often associated with red tide outbreaks. Organisms which cause theses blooms
around the United States are:
- Gonyaulax tamarenis,
along the Atlantic Northeast coast, ranging from the Canadian Maritimes to
Southern New England;
- Gonyaulax catenella,
on the Pacific West Coast from California to Alaska; and
- Ptychdiscus breve,
in the Gulf of Mexico along the West Florida coast.
Does it really color the
water?
Yes, water in coastal areas can be colored red by the algae,
thus the term "red tide." Although toxic blooms often turn the water reddish
brown, many nontoxic species or reddish brown plankton cause the same
discoloration. Conversely, toxic plankton may be numerous enough to toxify
shellfish, but not sufficiently abundant to discolor water. Discolored water
should always be regarded with suspicion.
What seafoods are unsafe
to eat from waters where red tide occurs?
Only a few marine animals
accumulate these toxins. Shellfish, are particularly prone to contamination as
they feed by filtering microscopic food out of the water. If toxic, planktonic
organisms are present, they are filtered from the water along with other
nontoxic foods.
Filter-feeding shellfish include quahogs, soft-shell
clams, oysters, mussels and scallops. Since toxins are stored in the digestive
tract (stomach) of these shellfish, scallops are safe to eat as long as only
cleaned muscle meat (the only part generally eaten) is consumed. Whelks and moon
snails can also accumulate dangerous levels of the toxin during red tide as they
feed on contaminated shellfish.
Lobsters, crabs, shrimp and finfish do
not accumulate toxin and are safe to eat from affected waters.
What happens if toxic
shellfish are consumed?
Eating toxic shellfish can cause paralytic
shellfish poisoning (PSP) in humans. PSP is caused by saxitoxin, which is
produced by G. tamarensis, and is one of the most potent toxins known to
scientists. After ingestion, this poison immediately affects the nervous system,
with symptoms usually occurring within 30 minutes. Severity depends on the
amount of toxin consumed. Initial reactions are tingling of the lips and tongue,
which spreads to the face, neck, fingertips and toes. Headache, dizziness and
nausea follow. These symptoms may be mistaken for drunken conditions and are
further aggravated by alcohol consumption. In severe cases, muscular paralysis
and respiratory difficulty may occur with 5 to 12 hours. Fatalities from
respiratory paralysis have been reported.
How are symptoms
treated?
Treatment varies with the severity of symptoms and can
include pumping the stomach, inducing vomiting and charcoal hemoperfusion (a
process involving the pumping of arterial blood through an activated charcoal
filter to remove the poison.) Alkaline fluids such as sodium bicarbonate are
also thought to be helpful in treating symptoms as the toxin is unstable in
alkaline conditions. Artificial respiration may be required if patients exhibit
respiratory stress.
What should one do if
accidental ingestion of toxic shellfish is suspected?
Seek proper
medical attention immediately. If a family doctor or other physician cannot be
reached, the person should be taken to the nearest hospital emergency room or
medical clinic. If none of these options are available, contact the nearest
poison control center.
How is red tide
monitored so that toxic shellfish are not marketed?
All shellfish
producing states have monitoring programs which test water, sediments and
shellfish for contamination. The established tolerance level for humans is 80
micrograms per 100 grams of raw edible meat. In Massachusetts, for instance, the
Department of Environmental Quality Engineering (DEQE) is responsible for
year-round testing of shellfish and shellfish growing areas. Monitoring efforts
are more intensive in the spring, summer and fall. The DEQE notifies the
Division of Marine Fisheries which, in turn, notifies affected city and town
officials of closures. When blooms subside, shellfish purify themselves of the
toxin, and when testing indicates a return to safe levels, the areas are
reopened. Monitoring programs may differ in other states.
What precautions should
recreational fisherman take?
Recreational shellfish gatherers should
look for posted warnings and pay close attention to local media announcements.
Also, it is advisable to contact appropriate state agencies for current news on
closures.
Under no circumstance should individuals harvest shellfish
from any area closed to shellfishing.
Toxic shellfish will taste and
appear no different than nontoxic shellfish, and cooking does not destroy the
red tide toxin. Testing is the only way to determine if shellfish contain unsafe
levels of toxin.
Should consumers feel
safe when purchasing shellfish at seafood markets?
Yes, consumers
should feel confidant about purchasing shellfish from established markets.
Harvesting regulations for shellfish are strictly enforced. Even during periods
of red tide, clams, oysters, mussels and whelks in seafood markets are harvested
from clean waters. The U.S. Food and Drug Administration visits state labs to
observe routine testing procedures, and public health officials regularly
monitor shellfish markets to ensure that only safe, nontoxic shellfish are
available to consumers.
For more information
contact:
- Massachusetts Department of
Public Health
Division of Food Drugs (617) 727-2670
emergencies (617)
522-3700
- Your local board of health
(listed in the phone book under local government)
- Your local Shellfish
Constable or Warden
- Massachusetts Department of
Fisheries, Wildlife & Law Enforcement
Division of Marine Fisheries (617)
727-3193
Reprinted from the Mass Dept of Public Health
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