Friday, November 4, 2011 at 08:31PM
Davao, 20 October 2011. Since 1983, some 540 outbreaks of red tide phenomenon have been recorded in the Philippines. The most recent outbreaks took place in Masinloc Bay, Zambales; Bolinao and Anda, Pangasinan; Murcielagos Bay in Zamboanga del Norte; and Dumanquillas Bay, Zamboanga del Sur.
Aside from the Philippines, red tide have also occurred in the temperate and tropical waters of Japan, eastern Australia, Malaysia (particularly in Sabah), United States, Peru, Chile, South Africa, England, Scandinavia, and Papua New Guinea.
Dr. Rafael D. Guerrero III, former director of the Philippine Council for Aquatic and Marine Resources Development (PCAMRD), said red tide is a natural phenomenon brought about by the bloom or predominance of a floating microscopic organism known as dinoflagellates. These “single-celled organisms can swim at the maximum rate of one meter per hour, by means of two whip-like flagella.”
The University of the Philippines at Los Baños (UPLB) said the name red tide was coined due to the sea water discoloration which ranges from amber, red, brown, yellow orange to purple caused by the highly-densed population of dinoflagellates. To make it short, its present name was given. In science, it is called harmful algal blooms (HABs).
Of the 2,000 dinoflagellates known, only 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 bahanse var. compressum. In medical parlance, red tide poisoning is referred to as paralytic shellfish poisoning (PSP).
The P. bahamense, according to Dr. Guerrero, is capable of horizontal and vertical movements in the water. 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 favorable conditions in the next outbreak.
Marine scientist Howard Seliger said that red tide is triggered by the increased nutrients in coastal currents. In his book, Biology, Epidemiology and Management of Pyrodinium Red Tide, he said that in the past there was not enough food in the currents to allow them to be carried over long distances.
But now, Seliger believes that more nutrients may be entering coastal waters “due to increased discharges of industrial and human wastes into waterways and decreased natural filtering due to deforestation.”
This finding has been bolstered by Dr. Teresita M. Espino of the National Institute of Molecular Biology and Biotechnology. “When there is so much waste, it becomes conducive to the growth of microorganisms that deplete the oxygen. The oxygen is eaten by the shellfishes which may cause the red tide incidence,” she explained.
The red tide organism that beset the Philippine waters, Seliger said, thrives only in coastal waters and lagoons under conditions of high salinity. It does not survive in freshwater bodies, he added.
“Humans die when they consume shellfish, particularly mussels, that are contaminated with red tide organisms,” Dr. Guerrero pointed out. Mussel is the common name given for any marine or freshwater bivalve mollusk closely related to oysters and scallops.
“Being filter-feeders, the mussels take in the red tide organisms from the water which are accumulated in their internal organs,” the former PCAMRD head explained.
Other shellfishes that filter-feed on the dinoflagellates include oysters and clams. Fish and other seafoods such as squids, shrimps, crabs, lobsters, and seaweeds are generally safe to eat even when caught from red tide infested waters provided they are washed thoroughly and the internal organs are removed.
Dr. Guerrero warned that people still get poisoned even if the mussels are cooked because the toxin is not destroyed by heat. The poison in the red tide organism 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 like adobo and paksiw, and the hydrochloric acid present in the human stomach.
Saxitoxin is detrimental to the nervous system. “Saxitoxin blocks the sodium channels of excitable membranes of the nervous system and associated muscles resulting in death by respiratory paralysis in extreme cases,” said Dr. Eric A. Tayag, one of the country’s noted epidemiologists.
Health officials said PSP victims have symptoms of tingling or burning sensation on the lips, tongue and face within 30 minutes after eating shellfishes with red tide organisms. The gastrointestinal symptoms are vomiting, abdominal pain, water diarrhea, nausea, and hypersalivation.
PSP-affected persons experience sensory abnormalities, numbness, dizziness, lightheadedness, headache, and short-tongue sensation. In severe cases, they cannot walk, and they breathe, swallow, and speak with difficulty. Some die from inability to breathe spontaneously.
Medical experts said that 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 supportive treatment can help, to keep the victim alive until the poison is eliminated.
Since there is still no known antidote to red tide poison, Dr. Guerrero said the best way to prevent PSP is to avoid the consumption of contaminated shellfishes during the ban imposed by the government authorities.
Levels exceeding 80 micrograms of toxin per 100 grams of shellfish meat warrant a ban on the harvest, sales, and ingestion of implicated shellfishes, according to the World Health Organization.
In the Philippines, a ban is issued when the toxic levels have exceeded 40 micrograms of toxin per 100 grams of shellfish meat.
Red tide is here to stay. But those living near the coastal areas can help obliterate the red tide-causing organisms by using a ball made of clay. “Algal cells die when they stick to clay particles,” according to Dr. Rhodora V. Azanza, program leader of PhilHABS and co-project leader for the ball clay technology. “Clay minerals further entrail the algal cells as they settle at the sea floor.”
During a red tide problem in Masinloc Bay, Zambales recently, the efficiency of ball clay application was put to test. A prototype clay dispersal unit formed the clay balls which were applied on algal blooms. The unit mixes ball clay particles with seawater drawn from the area. Mixing ball clay with seawater will improve the efficiency of ball clay to collide and eventually aggregate with algal cells.
The team found that the cells of Pyrodinium at the surface and bottom of the sea were not present after clay application. The study also showed no negative effects on other marine organisms such as green mussels and milkfish, among others.
PhilHABs is a University of the Philippines-led program supported by Department of Science and Technology through PCAMRD. It has done intensive studies in 10 areas affected by red tides, namely: Manila Bay; Sorsogon Bay, Sorsogon; Bolinao and Anda, Pangasinan; Matarinao Bay, Eastern Samar; Cancabato Bay, Leyte; Murcielagos Bay, Zamboanga del Norte; Balete Bay, Davao Oriental; Pujada Bay, Davao Oriental; and Benoni Lagoon, Camiguin.
Aside from Pyrodinium, PhilHABs has identified Alexandrium sp. and Gymnodinium catenatum as other causal organisms for PSP. Organisms causing diarrhetic shellfish poisoning (DSP) are Dinophysis miles, Dinophysis acuminata, Dinophysis caudata, and Prorocentrum lima. Some Pseudonitzschia species may cause amnesic shellfish poisoning (ASP).