Red tides and paralytic shellfish poisoning in the Philippines

Toxic marine dinoflagellate blooms have been recognized for many years to have a significant impact on the utilization of shellfish resources and human health because of the problem of paralytic shellfish poisoning (PSP), which occurs in many areas of the world and seems to be intensifying and spreading (Prakash et al. 1971; Taylor and Seliger 1979). Less than 20 dinoflagellate species are known or thought to produce toxins (Steidinger 1979). Many filter-feeding shellfish, such as clams, mussels, and scallops, feed on several of these red tide forming toxic dinoflagellates and accumulate the toxins in their tissues without themselves being affected (Prakash et al. 1971; Twarog 1974; Hashimoto 1979). As a consequence, it may become a serious problem when the affected shellfish are eaten by warm-blooded animals that are particularly sensitive to the toxin. In extreme cases, several species of clams and mussels may prove fatal if eaten by man. To date, research efforts to develop an antidote for the toxins have been relatively unsuccessful (Yentsch and Incza 1980) and the only effective control measure is the closure of the affected areas to shellfish gathering. Paralytic shellfish poisoning has long been known as a serious problem in four regions of the world, namely Europe, North America, the Pacific coast, and Asia (Twarog 1974). There are medical records of over 1650 cases of this food poisoning worldwide, which have resulted in at least 300 fatalities (Dale and Yentsch 1978). Jay (1970) asserted that paralytic shellfish poisoning in man has a mortality rate close to 10% and as much as 22% in some areas. Most recently, red-tide outbreaks were reported in tropical Indo-Pacific countries such as Papua New Guinea (1972 until early 1976), Brunei and Sabah (March-May 1976) and the Philippines (mid-1983). The major species involved in the tropical IndoPacific red tides was the armoured, bioluminescent dinoflagellate Pyrodinium bahamense Plate 1906, which was recently reclassified as Pyrodinium bahamense var. compressa Böhm 1931 (Steidinger et al. 1980), a species that is closely related to Protogonyaulax (= Gonyaulax spp.) (Fig. 1), and was unreported in the region before 1971 (Maclean 1979). The organism was first described from Waterloo Lake, a small, shallow, saline lagoon in Nassau, Bahamas, in 1906 (Beales 1976) and its previous known distribution was restricted to the tropical and subtropical waters of the Caribbean Sea (particularly Jamaica and Puerto Rico), eastern Pacific Ocean, Red Sea, Persian Gulf, and North Atlantic Ocean (Wall and Dale 1969) where it was reported to be nontoxic (Beales 1976). It has now, however, been found to be responsible for fatal paralytic shellfish poisonings in Papua New Guinea (Worth et al. 1975), Brunei and Sabah (Beales 1976), and the Philippines (Estudillo 1984). Harmful dinoflagellate blooms of Pyrodinium bahamense var. compressa and the paralytic shellfish poisoning it causes were experienced for the first time in Philippine waters when they occurred along the coast of Eastern Visayas northwestward to the coast of Masbate and Sorsogon during the period from late June to early September 1983 (Fig. 2). In the latter part of September, cases of paralytic shellfish poisoning involving one fatality were reported in Western Visayas. Severely affected by the red tide were the mariculture project farms in Maqueda Bay and Villareal Bay (western Samar), where green bay