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

RED TIDE§ IN THE INDO-WEST PACIFIC REGIONGUSTAAF M. HALLEGRAEFFCSIRO Marine LaboratoriesGPO Box 1538Hobart, Tasmania 7001AustraliaABSTRACTThe most common red tide organisms in Indo-West Pacific waters, the blue-green algaTrichodesmium erythraeum and the dinoflagellate Noctiluca scintillans, produce mostly harmlesswater discolourations. Only in exceptional cases do such plankton blooms cause fish kills in shelteredbays due to the generation of anoxic conditions. The raphidophyte flagellate Chattonella marina hascaused fish kills in India by releasing free fatty acids that destroy the gill tissues of fish. There isevidence that some red tide problems (e.g. Chattonella, Noctiluca) are aggravated by industrialpollution, but other plankton blooms (e.g. Trichodesmium) bear no relationship to eutrophication.Red tides caused by toxic dinoflagellates, which produce potent neurotoxins that can find theirway through fish and shellfish to man, are well documented from Europe, North America and Japan.At present, paralytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP) and ciguatera fishpoisoning are *ually unknown from the Central Indian Ocean. Admittedly, surveys for the causativedinoflagellate species have been inadequate, and ethnic dietary habits (low shellfish consumption) mayalso play a role. Attention is drawn to the apparent spreading of Pyrodinium bahamense var.compressa (PSP) through the East Indies (Papua New Guinea, Philippines, Malaysia, Indonesia), andProtogonyaulax tamarensis has caused recent PSP fatalities in Thailand and possibly India.It is recommended that a basic training workshop be conducted for local workers responsiblefor microscopic plankton taxonomy to enable them to recognize potentially toxic species and theirbenthic cysts. In addition, public health officials should be made aware of the clinical symptoms ofvarious types of shellfish and fish poisoning to ensure that, if necessary, warnings can be issuedpromptly and effectively.INTRODUCTIONRed tides are blooms of unicellular marine plankton algae which become so dense that theydiscolour the sea (e.g. Red Sea). Plankton blooms also may appear yellow, brown, green, blue ormilky in colour dependent upon the organism involved. Red tide species in the Indo-West Pacificregion include representatives of the blue-green algae, dinoflagellates and raphidophytes, with diatomsand prymnesiophytes only rarely involved. Most red tides are caused by motile or strongly buoyantspecies, and their high concentrations are achieved through a combination of high growth rates andvertical (behavioural) or horizontal (physical) aggregation. Dense plankton concentrations aretherefore most strongly developed under stratified stable conditions, at high temperatures andfollowing high organic input from land run-off after heavy rains.The majority of plankton blooms appear to be completely harmless events, but underexceptional conditions non- toxic bloom-formers may become so densely concentrated that theygenerate anoxic conditions that cause indiscriminate kills of fish and invertebrates in sheltered bays(GRINDLEY and TAYLOR, 1962). Oxygen depletion can result from high respiration by the algae (atnight or in dim light during the day), but more commonly it is caused by bacterial respiration duringdecay of the algal bloom. A basically different type of phenomenon involves the production bydinoflagellates of potent toxins that find their way through fish or shellfish to man. In this case lowdensities of the toxic algae in the water column may be sufficient to cause such illnesses in humans asparalytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP) and ciguatera fish poisoning.PSP can result both from eating bivalve shellfish and planktivorous fish (clupeotoxicity), while DSP is105