Red Tide Fact Sheet

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Red Tide (Paralytic Shellfish Poisoning)

What is Red Tide?
Red Tide is caused by a = "population=20 explosion" of toxic, naturally occurring microscopic plankton = (specifically, a=20 subgroup known as dinoflagellates). "Blooms" of the poison-producing = plankton=20 are coastal phenomena caused by environmental conditions, which promote=20 explosive growth. Factors that are especially favorable include warm = surface=20 temperatures, high nutrient content, low salinity, and calm seas. Rain = followed=20 by sunny weather in the summer months is often associated with red tide = blooms.=20 Organisms that cause theses blooms around the United States are as follows:

Alexandrium fundyense, along the Atlantic Northeast coast, ranging = from=20 the Canadian Maritimes to Southern New England;
Alexandrium catenella, on the Pacific West Coast from = California to=20 Alaska; and
Karonia brevis, in the Gulf of Mexico along the West=20 Florida coast.

Does it really color the water?
Yes, water in = coastal=20 areas can be colored red by the algae, thus the term "red tide." = Although toxic=20 blooms often turn the water reddish brown, many nontoxic species or = reddish=20 brown plankton cause the same discoloration. Conversely, toxic plankton = may be=20 numerous enough to toxify shellfish, but not sufficiently abundant to = discolor=20 water. Discolored water should always be regarded with suspicion. = However, it=20 should be noted that even during high concentrations during a red tide = event=20 caused by Alexandrium fundyense, there is no risk with regard to = swimming in the=20 water.

What seafoods are unsafe to eat from waters where red tide=20 occurs?
Only a few marine animals accumulate these toxins.=20 Shellfish, including hard-shell clams, soft-shell clams, oysters, = mussels and=20 scallops, are particularly prone to contamination as they feed by = filtering=20 microscopic food out of the water. If toxic planktonic organisms are = present,=20 they are filtered from the water along with other nontoxic foods. Whelks = and=20 moon snails can also accumulate dangerous levels of the toxin during red = tide as=20 they feed on contaminated shellfish.

During red tide blooms, hard-shell clams, soft-shell clams, oysters, = mussels,=20 whelks, and moon snails harvested from areas affected by the blooms are = not safe=20 to eat. Since toxins are stored in the digestive tract (stomach) and = viscera=20 (intestines) of these animals, scallops are safe to eat as long as only = cleaned=20 adductor muscle (the only part generally eaten) is consumed. Lobster = meat,=20 crabs, shrimp, and most finfish do not normally accumulate toxin and are = safe to=20 eat from affected waters. Lobster tomalley (the green part or liver) is = not safe=20 to eat in general, and particularly during red tide events because this = part of=20 the lobster can build up high levels of toxins and other pollutants.

What happens if toxic shellfish are = consumed?
Eating=20 toxic shellfish can cause paralytic shellfish poisoning (PSP) in humans. = PSP is=20 caused by saxitoxin, which is produced by Alexandrium fundyense and is = one of=20 the most potent toxins known to scientists. After ingestion, this poison = immediately affects the nervous system, with symptoms usually occurring = within=20 30 minutes. Severity depends on the amount of toxin consumed. Initial = reactions=20 are tingling of the lips and tongue, which spreads to the face, neck, = fingertips=20 and toes. Headache, dizziness and nausea follow. These symptoms may be = mistaken=20 for drunken conditions and are further aggravated by alcohol = consumption. In=20 severe cases, muscular paralysis and respiratory difficulty may occur = within 5=20 to 12 hours. Fatalities from respiratory paralysis have been = reported.

What should one do if accidental ingestion of toxic shellfish = is=20 suspected?
Seek proper medical attention immediately. If a = family=20 doctor or other physician cannot be reached, the person should be taken = to the=20 nearest hospital emergency room or medical clinic. If none of these = options are=20 available, contact the nearest poison control center. The diagnosis of = PSP is a=20 reportable disease. Cases of suspected PSP poisoning should be reported = to the=20 Center for Environmental Health, Food Protection Program, at = 617-983-6712 or to=20 the Center for Hospitals and Clinical Laboratories, Bureau of = Communicable=20 Disease Control, at 617-983-6800.

How is red tide monitored so that toxic shellfish are not=20 marketed?
All shellfish-producing states have monitoring = programs=20 that test water, sediments, and shellfish for contamination. The action = level=20 for humans is 80 micrograms per 100 grams of shellfish meat. In = Massachusetts,=20 for instance, the Division of Marine Fisheries (DMF) is responsible for=20 year-round testing of shellfish and shellfish growing areas. Monitoring = efforts=20 are more intensive in the spring, summer and, fall. The DMF notifies = affected=20 city and town officials of closures. When blooms subside, shellfish = purify=20 themselves of the toxin, and when testing indicates a return to safe = levels, the=20 areas are reopened. Monitoring programs may differ in other states.

What precautions should recreational fisherman=20 take?
Recreational shellfish gatherers should look for = posted=20 warnings and pay close attention to local media announcements. Also, it = is=20 advisable to contact appropriate state agencies and local shellfish = constables=20 for current news on closures.

Under no circumstance should individuals harvest shellfish from any = area=20 closed to shellfishing.

Toxic shellfish will taste and appear no different than nontoxic = shellfish,=20 and cooking does not destroy the red tide toxin. Testing is the only way = to=20 determine if shellfish contain unsafe levels of toxin.

Should consumers feel safe when purchasing shellfish at = seafood=20 markets?
Yes, consumers should feel confidant about = purchasing=20 shellfish from established markets. Harvesting regulations for shellfish = are=20 strictly enforced. Even during periods of red tide, clams, oysters, = mussels and=20 whelks in seafood markets are harvested from clean waters. The U.S. Food = and=20 Drug Administration visits state labs to observe routine testing = procedures, and=20 public health officials regularly monitor shellfish markets to ensure = that only=20 safe, nontoxic shellfish are available to consumers.

For more information contact:

Massachusetts Department of Public Health Bureau of Environmental = Health,=20 Food Protection Program (617) 983-6712; or the Bureau of Communicable = Disease=20 Control (617) 983-6800.

Your local board of health (listed in the phone book under local=20 government)
Your local Shellfish Constable or Warden
Massachusetts Division of Marine Fisheries (617) 626-1520 or (508) = 563-1779; you may also visit the DMF web site at www.mass.gov/dfwele/dmf/programsandprojects/psp_notice.htm#she= lsani

This information is provided by the Food=20 Protection Program within the Department=20 of Public Health.

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