coasts and oceans > features > deadly red tides on the rise
Deadly red tides on the risePosted: 06 Dec 2004
by Henrylito Tacio
Red tides which poison coastal communities and marine life are increasing in frequency and toxicity thanks, at least in part, to pollution from human activities on land. They are now becoming a problem in the Philippines, as Henylito Tacio reports from Mindanao.
On a sultry morning of July 2003, the people awoke to thousands of dead fish floating along the Dumanquillas Bay in Western Mindanao. Millions of pesos worth of marine products were lost while around 10,000 residents were deprived of a source of income.
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Red tides are an increasing threat to Pacific coastlines.
© Canadian Ministry for Fisheries and Oceans
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Scenarios like this are becoming more common in Philippines water since 1983, when the first red tide incident occurred in Maqeuda Bay, Samar. Four years later, it recurred in Samar and was also reported in Zambales. After that, the problem has spread to other parts of the country.
But how the red tide organism turned up in the
Philippines still baffled Filipino scientists. Some speculated that the red tide-causing organism could have hitchhiked across the oceans in ships plying between the Philippines and other Pacific countries where the organism is endemic. Others thought ocean currents could have carried the organism.
Population explosion
Dr. Rafael D. Guerrero III, director of the Laguna-based Philippine Council for Marine and Aquatic Research and Development (PCAMRD), says red tide is a natural phenomenon brought about by a population explosion of floating microscopic organisms known as 'dinoflagellates.' These "single-celled organisms can swim at the maximum rate of one metre per hour, by means of two whip-like flagella," he says.
The red tide organisms develop astonishingly fast.
According to experts, an alga - as the organism is
called - can replicate itself a million times in just two to three weeks until they cover the surface of the sea. "The phenomenon, though colourful in appearance, is very dangerous because it can lead to the death of aquatic life and therefore cause damage to the fishing industry," warned Pan Yue, vice-minister at the State Environmental Protection Administration in China, another country beset by the problem.
A red tide phenomenon in Hong Kong seawaters in 1999 cost the territory's fishing industry millions of dollars in damage as fish farms had to throw out tons of contaminated stocks.
The phenomenon is called "red tide" because of the
reddish colour, which 'dinoflagellates' gives to the sea when present in high cell densities. There's a story in the Bible of how water turned to blood in the land of Egypt. That may have been the earliest written account of a "red tide."
Enriched nutrients
Of the 2,000 'dinoflagellates' known to science, only about 20 species produce toxins or poisonous substances that kill humans. The red tide organism that caused deaths in the country has been identified as 'Pyrodinium bahamense var. compresa.' "This species is capable of horizontal and vertical movements in the water," Dr Guerrero explains. "Being attracted to sunlight, it rises up to the surface during daytime and settles at the bottom in the dark hours."
The organism multiplies rapidly through asexual means (without sex cells) during its productive stage which results in bloom. For its resting or dormant stage, the organism reproduces sexually and form cysts which "hibernate" in the sediment until activated by favourable conditions in the next outbreak.
Experts say there are three conditions that trigger red tides. The first is stirring up of the sediment in the nearshore waters by wind action. The second is the high temperature of the water due to summer sun which makes the sea saltier. The third condition is the nutrient enrichment of the sea.
Untreated sewage
Nutrient enrichment may be in the form of pollution from sewage, fertilizer, car emissions and industrial waste. Outflows of untreated sewage on the east China coast are blamed for the red tides in seawaters near Shanghai. "Dumping untreated household sewage into the East China Sea is increasing the frequency of red tides," Wu Zhennan, vice-director of the State Oceanography Bureau's environmental department.
How bad is red tide? "Red tides release harmful toxins causing mass mortalities of various marine organisms," explains Wendy Hopkins, who created The Pollution Solution Team based in Naples, Florida. "They are also responsible for numerous deaths of at least three endangered marine mammals: Humpback whales, bottle-nosed dolphins, and Florida manatees."
Over the years, the poisons from the algal blooms have caused sickness and death to thousands of people throughout the world. "The impact to human health is primarily from eating seafood that has been contaminated with red tide toxins," Ms. Hopkins says.
"Most affected are bivalves such as oysters, clams, scallops and mussels. Fish, shrimp and crabs are usually safe for consumption."
"Humans die when they consume shellfish, particularly mussels, that are contaminated with red tide organisms," reveals Dr. Guerrero. "Being
filter-feeders, the mussels take in the red tide
organisms from the water which are accumulated in
their internal organs."
Dangerous poisons
According to Dr Guerrero, people still get poisoned even if the mussels are cooked because the toxin is not destroyed by heat. The poison in the red tide organisms is known as saxitoxin, a water-soluble salt that affects the nervous system.
The potency of saxitoxin has been reported to increase by acidic chemicals like vinegar used in preparing common Filipino dishes such as 'adobo' and 'paksiw,' and the hydrochloric acid present in the human stomach.
"Being neurotoxic or detrimental to the nervous
system," says Dr Guerrero, "saxitoxin causes death by paralysis of the breathing apparatus in man." In medical parlance, red tide poisoning is referred to as paralytic shellfish poisoning (PSP).
Officials from the Department of Health say PSP
victims have symptoms of tingling or burning sensation on the lips, tongue and face within 30 minutes after eating contaminated shellfishes. A general feeling of numbness, loss of muscle control, giddiness, drowsiness, fever, rash, nausea and vomiting follow. Death is reportedly due to respiratory arrest.
Growing threat
Seek proper medical attention immediately, medical
experts advised. If recognized early, the shellfish poison can still be eliminated from the stomach by inducing vomiting or washing it out (lavage through a stomach tube). But once the poison has entered the circulation, only upportive treatment can help, to keep the victim alive until the poison is eliminated.
Dr. Guerrero says the best way to prevent red tide poisoning is to avoid the consumption of contaminated shellfishes during the ban imposed by the government authorities. In other countries where red tides also commonly occur like Japan, Canada, and the United States, annual bans on specific months of the year take effect to protect the consuming public.
Dr. Paul Epstein of the Harvard Medical School, who has extensively studied the red tide phenomenon, notes that the intensity, duration and extent of harmful algal blooms is increasing and so is their toxicity. Unless they can be prevented, these toxic sea-gardens pose a growing threat to marine life, the economy of coastal communities, and the health and well-being of people around the world.
Henrylito Tacio is People & the Planet contributing editor in East Asia.
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