RED TIDE:
Not every plant poisoning is caused by a large, terrestrial plant.
Several microscopic marine algae are notoriously poisonous to hapless humans who consume them in shellfish.
These
Algae are tiny, single-celled plants that, like plants on land, capture and use the sun's energy to grow. The growth of algae
is an essential life process, as it is the first step in transferring solar energy into aquatic food webs. The huge variety
of marine algae are typically subject to annual cycles of growth & decay. These organisms thrive and multiply principally
during the spring and summer, in response to increased light intensity and favourable levels of salinity & nutrients in
ocean water. During the growth period, or bloom, each single algae cell may replicate itself one million times in two to three
weeks.
During the reproductive riot of the bloom, warm, shallow seawater tends to become discoloured by the sheer
concentration of algae seeking the sunlight. This discolouration is a result of the various pigments the plants use to trap
sunlight; depending on the species of algae present, the water may reflect pink, violet, orange, yellow, blue, green, brown,
or red. Since red is the most common pigment, the phenomenon has come to be called Red Tide.
Most species contributing
to algal blooms are harmless, BUT (another big but!) some species are poisonous to animals which feed upon them directly or
indirectly. Some of the toxins these species produce are seriously toxic. Often, the algae themselves are unaffected, as are
the filter feeders, especially shellfish, for whom micro-algae are the principal diet. However, to carnivores further up the
food chain, including humans, these toxins are potentially FATAL.
As in the case of poisonous fungi, scientific knowledge
of poisonous algae is incomplete; indeed, new and alarming toxic algae are still coming to light. In Nova Scotia, however,
three different algae are known to cause three, distinct, severe to deadly poisonings:
* Alexandrium causes Paralytic
Shellfish Poisoning (PSP)
* Dinophysis causes Diarrhetic Shellfish Poisoning (DSP)
* Pseudo-nitzschia multiseries
causes Amnesic Shellfish Poisoning (ASP)
.
CLICK on the names above for a microscopic view and specific information.
POISON LOCATION
THE GUTS AND INTESTINAL TRACT of shellfish and fish which have consumed toxic algae accumulate
and store the toxins. As a result, fish, provided they are gutted in the usual manner, are not a threat; nor, ironically,
are scallops- a shellfish whose "meats"- the muscles that open and close its shell- are the only parts harvested for food.
All other infected shellfish, however- especially mussels, oysters & clams- may cause ASP, PSP, or DSP because they are
eaten whole.
POISON TYPE
DOMOIC ACID is an amino acid-based toxin which is potentially lethal. Tiny amounts can
have deadly results (see below) in humans. Algal blooms can also cause other problems besides toxicity. When an algae bloom
dies back in a shallow bay, oxygen-depleting bacteria may thrive on the dead algae and so kill fish and other marine life.
Sometimes floating algae cut eelgrass beds off from sunlight, robbing shellfish of habitat. On fish farms, concentrations
of algae can simply clog the gills of the fish, causing respiratory failure.
TYPICAL POISONING SCENARIO
Almost
all incidents involve the accidental ingestion of mussels, clams, oysters or other shellfish affected by toxic algae. Since
there is no visual method for determining whether particular shellfish are affected, Canada has been carrying out extensive
laboratory monitoring of shellfish toxicity since 1943. As soon as these routine studies detect dangerous concentrations of
toxic algae, Fisheries and Oceans Canada posts affected beaches and estuaries with orders closing them to shellfish harvesting.
It is dangerous to ignore these signs, which are commonplace in Nova Scotia during the warmer months. Little wonder
that folklore warns us not to eat shellfish in months with no "r" in their names! By the mid-Eighteenth Century, shellfish
poisoning was so commonplace as to give rise to the London proverb, "There is no venturing on oysters, Sir, or women of the
town"...
SYMPTOMS
Shellfish poisoning, of whatever sort, is UNPLEASANT AND OFTEN LETHAL. The onset of symptoms
occurs as soon as the victim's digestive system starts to work on the infected shellfish. In the case of paralytic shellfish
poisoning (PSP), the toxin attacks the nervous system and causes paralysis. There is no antidote; death occurs from asphyxiation
or respiratory paralysis.
PSP has been known since biblical times; what is thought to be PSP figures in the Book of
Exodus, and the Red Sea is thought to have been named for the signs of frequent blooms of algae. Not for nothing did the Judaic
Partriarchs proscribe shellfish...
The first recorded case in Canada, however, occurred in 1793, during Captain George
Vancouver's expedition to what is now British Columbia, when John Carter, a seaman, died from the effects of eating mussels,
presumably infected with toxic algae. An eyewitness account of his death occurs in the June 17 diary entry of the expedition
naturalist and surgeon, Archibald Menzies.
Diarretic Shellfish poisoning, as the name suggests, causes extreme gastrointestinal
upset; DSP is less dangerous than PSP, but failure to treat the diarrhoea may lead to death from dehydration or other complications.
Domoic acid, which causes amnesic shellfish poisoning, binds to chemical receptors in brain cells and causes their
dysfunction. The poisoning begins with stomach upset, rapidly followed by dizziness, disorientation, and memory loss- symptoms
which often persist indefinitely. During a 1987 outbreak on PEI, 1% of the reported poisonings resulted in death from brain
damage.
What is red tide?
Photomicrograph of red tide organism
Photomicrograph courtesy of
Dr.
Tracy Villareal, UTMSI.
Red tide is a naturally-occurring, higher-than-normal concentration of the microscopic algae
Karenia brevis (formerly Gymnodinium breve).
This organism produces a toxin that affects the central nervous system
of fish so that they are paralyzed and cannot breathe. As a result, red tide blooms often result in dead fish washing up on
Gulf beaches. When red tide algae reproduce in dense concentrations or "blooms," they are visible as discolored patches of
ocean water, often reddish in color.
What causes red tide?
Red tide is a natural phenomenon not caused by
human beings. When temperature, salinity, and nutrients reach certain levels, a massive increase in Karenia brevis algae occurs.
No one knows the exact combination of factors that causes red tide, but some experts believe high temperatures combined with
a lack of wind and rainfall are usually at the root of red tide blooms. There are no known ways that humans can control it,
but many scientists around the world are studying red tide at present. It's important to remember that red tide has happened
before and the Texas marine environment has always recovered.
How, when and where do red tide blooms start?
Texas
red tides have occurred from August through February. They typically begin in the Gulf of Mexico. Currents and winds then
transport blooms toward shore. The blooms mainly come up along Gulf beaches, and less frequently into bays and estuaries.
Where is the red tide on the Texas coast right now?
Red tide in Texas bay
It's almost impossible to say
exactly where the red tide is at any given moment, because blooms constantly expand and contract and move around in response
to winds and tides. It's important to realize that red tides are typically isolated patches that don't blanket every stretch
of beach. They often concentrate around wind- or tide-protected areas like man-made jetties.
How can I get the latest
information on the current red tide?
Texas Parks and Wildlife has set up a menu item on its main toll-free information
line to provide regularly updated reports on the current red tide event. Phone 800-792-1112, press 4 for fishing, then 9 for
red tide information. Red tide updates will also appear on this web site each time that an update is provided by biologists.
Red tide in Texas bay
Should I consider postponing a trip to the coast right now?
Dave Buzan, head of
the Texas Parks and Wildlife Department's Kills and Spills Team, had this to say on the subject... "If it were my family heading
to the coast, I would not cancel a vacation because of red tide. It's an isolated, patchy phenomenon that does not blanket
every stretch of beach. On any given day, there are generally miles of good beach and clean water for beach-goers and anglers
to enjoy. However, we encourage all travelers to heed the advice of the Texas Department of State Health Services, get the
current facts and draw their own conclusions, since different people have different comfort levels with these kinds of situations."
Is it safe to eat fish that I catch in or near the red tide?
It's usually okay to eat fish, crabs and shrimp
during a red tide bloom because the toxin is not absorbed into the fleshy tissues of these animals. This advice from the Texas
Department of State Health Services is based on the assumption that only the "edible" portions are being consumed (the fillet
or muscle). Keep in mind that you should never eat fish found sick or dead, whether or not they are caught during a red tide.
Why doesn't the state post signs on the beach warning the public about red tide?
The eye and throat irritation
caused by red tide results from high concentrations of the algae and rough surf. These conditions cause the red tide's irritant
to become suspended in the air in the salt spray. There is typically little or no irritation when surf conditions are relatively
calm. In most red tides in Texas, these conditions vary a lot within the space of days or even hours. As a result, the same
part of the beach may have irritating conditions in the morning and those conditions may be gone by afternoon. On a calm day,
even with red tide in the surf zone, many people can enjoy the beach because there is not a lot of salt spray from the surf
carrying irritant to the beach. The best advice for beach visitors is if they feel effects in an area, leave that area and
try another one. Some local authorities will post signs on beaches that they manage. Be aware of all beach warnings when visiting
the beach.
Is it safe to eat oysters during a red tide?
Oysters and other shellfish such as clams, mussels,
whelks and scallops can accumulate red tide toxins in their tissues. People that eat oysters or other shellfish containing
red tide toxins may become seriously ill with neurotoxic shellfish poisoning (NSP). Once a red tide appears to be over, toxins
can remain in the oysters for weeks to months. For this reason, the Texas Department of State Health Services (TDSHS) closely
monitors oyster growing areas for the presence of red tide and red tide toxins. TDSHS has the authority to close shellfish
harvesting areas during and after a red tide. Oysters you buy from a restaurant or certified shellfish dealer should not have
red tide toxins in them because of the TDSHS’s monitoring program. There are, however, other risks associated with
bacteria and other contaminants in raw oysters. For more information about consuming oysters, consult a physician or health
authorities such as TDSHS. To find more information on Vibrio vulnifcus, which may be cpntracted by eating raw oysters, please
refer to the TDSHS Vibrio Fact Sheet (PDF.)
A Fish Kill on a Texas bay
Where can I get more information on red
tide?
Call the red tide phone information line mentioned above -- dial (800) 792-1112, at the menu select fishing
and then red tide, or call the Texas Parks and Wildlife Kills and Spills Team at (512) 912-7055.
How can I report
dead fish or a possible sighting of red tide?
You can phone the TPW Kills and Spills Team at (512) 912-7055
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