139736eo.pdf (20MB) - Japan Oceanographic Data Center

diarrhetic shellfish poisoning (DSP). The Dinophysis-toxin involved has also been detected in NewZealand mussels. Humans can be poisoned through eating mussels and to lesser extent scallops andoysters. The clinical symptoms (Table 1) are easily confused with those of bacterial gastric infections,and DSP (first described in 1976 in Japan) may be much more common than realised at present.Control measures include seasonal closures of the shellfishery, purification of shellfish in laboratorytanks, and removal of the toxin-accumulating hepatopancreas from scallops before eating (notpracticable with mussels and oysters).Gambierdiscus toxicus Adachi et Fukuyo: This lens-like, benthic dinoflagellate (Fig. 15a) appears inepiphytic association with bushy red, brown and green seaweeds and can also be found free insediments and coral rubble. The alga is probably circum-tropical in distribution, but thus far is onlyknown from the Great Barrier Reef region (Australia), the Pacific Islands and possibly Mauritius andthe Seychelles (D. ARDILL, unpublished data). Gambierdiscus has not yet been recorded from NewGuinea, Indonesia, the Philippines, Thailand or India. Because of its dislike of land runoff, thespecies seldom occurs near large landmasses. Captain COOK suffered from the tropical fishpoisoning “ciguatera” when visiting New Caledonia in 1774, but the causative dinoflagellate organismwas only identified in 1978 (ADACHI and FUKUYO, 1979). The potent neurotoxins ciguatoxin andmaitotoxin accumulate through the food chain, from small fish grazing on the coral reefs into theorgans of bigger fish that feed on them. Control measures include eating only smaller fish and noteating species such as red bass, coral trout, chinaman fish, barracuda and moray eel (Table 3). Over400 cases of ciguatera food poisoning are known from Australia (GILLESPIE, 1980) and over 3000cases from French Polynesia. No adequate treatment is yet available. The symptoms persist formonths and recur up to several years later (Table 1). The associated benthic dinoflagellatesOstreopsis siamensis Schmidt (Fig. 15b) and Prorocentrum lima (Ehr.) Dodge (Fig. 1%) also exhibitsome toxicity (FUKUYO, 1981) similar to ciguatera.CONTROL OF RED TIDESRed tides can cause great economic damage, affecting both the seafood market and tourism.Destruction of fish and shellfish by anoxia and poisoning of fish and shellfish by toxin producingdinoflagellates are especially critical in countries that depend heavily on mariculture for protein.Cooking and other treatments of fish and shellfish do not destroy the toxins. The question arises as towhether these events can be controlled artificially. Various chemical and biological control methodsthat have been attempted have had mostly negative results. Copper sulphate was sprayed from planesto combat Florida red tides of Ptychodiscus brevis (STEIDINGER, 1983), but the killed algal cellsreleased their endotoxins into the seawater and the decomposing algal mass generated anoxicconditions. Seed cultures of various predators, parasites or pathogens have been considered ascandidates for biological control. However, the successful predator would accumulate the toxin andthus become a highly toxic vector to higher trophic levels in the food chain.Moderate-scale coastal engineering involving deepening or filling affected areas or reshapingthe coastline or diverting rivers may be a viable option to combat anoxic conditions in sheltered bays.Marine dredging operations should be alerted to the possible danger of seeding benthic dinoflagellatecysts into the water column, and caution should be used when transferring shellfish from one area toanother because resistant microscopic cysts could easily be carried with them. Red tides that arerelated to increasing eutrophication (e.g. Chattonella in Japan) can be controlled by reducing dischargeof sewerage and industrial wastes. On the other hand, phenomena such as PSP and ciguatera, whichwere known centuries before the modem industrial world developed, should be regarded as completelynatural events. Careful monitoring of the causative dinoflagellates, of their cysts and of associatedseafood products appears to be the only solution at present. Dependent upon the results, controlmeasures may include elimination of the toxin-accumulating organs from fish or shellfish, avoidanceof certain seafood species, depuration of shellfish in laboratory tanks and, in extreme cases, seasonalclosures of particular fisheries.109