Impacts of climate change on harmful algal blooms and seafood safety

In a strict sense, harmful algal blooms are completely natural phenomena that haveoccurred throughout recorded history. However, even non-toxic algal blooms canhave devastating impacts when they lead to kills of fish and invertebrates by generatinganoxic conditions in sheltered bays. Other algal species, although non-toxic tohumans, can produce exudates that can cause damage to the delicate gill tissues of fish(raphidophytes Chattonella, Heterosigma, and dinoflagellates Karenia, Karlodinium).Whereas wild fish stocks are free to swim away from problem areas, caged fish inintensive aquaculture operations are trapped and, thus, can suffer devastating mortalities.Of greatest concern to human society are algal species that produce potent neurotoxinsthat can find their way through shellfish and fish to human consumers where theyevoke a variety of gastrointestinal and neurological illnesses. One of the first recordedfatal cases of food poisoning after eating contaminated shellfish happened in 1793,when Captain George Vancouver and his crew landed in British Columbia (Canada)in an area now known as Poison Cove. He noted that, for local Indian tribes, it wastaboo to eat shellfish when the seawater became bioluminescent due to algal bloomsby the local dinoflagellate Alexandrium catenella/tamarense, which is now known tobe a causative organism of PSP. The increase in shellfish farming worldwide is leadingto more reports of PSP, DSP (first documented in 1976 in Japan), NSP (reported fromthe Gulf of Mexico as early as 1844) and ASP (first identified in 1987 in Canada). Theexplorer Captain James Cook already suffered from the tropical illness of CFP fromfish when visiting New Caledonia in 1774. Worldwide, almost 2 000 cases of foodpoisoning from consumption of contaminated fish or shellfish are reported each year.Some 15 percent of these cases prove fatal. If not controlled, the economic damagethrough the slump in local consumption and exports of seafood products can beconsiderable. Whales and porpoises can also become victims when they receive toxinsthrough the food chain via contaminated zooplankton or fish. In the United Statesof America, poisonings of manatees in Florida via seagrasses and, in California, ofpelicans and sea lions via contaminated anchovies have also been reported (Hallegraeff,Anderson and Cembella, 2003). In the past three decades, harmful algal blooms seem to have become more frequent,more intense and more widespread. Four explanations for this apparent increase inalgal blooms have been proposed: (i) a greater scientific awareness of toxic species;(ii) the growing utilization of coastal waters for aquaculture; (iii) the stimulationof plankton blooms by domestic, industrial and agricultural wastes and/or unusualclimate conditions; and (iv) the transportation of algal cysts either in ships ballastwater or associated with moving shellfish stocks from one area to another (Hallegraeff,1993). Few long-term records exist of algal blooms at any single locality; ideally, at least30 consecutive years of data would be needed. Therefore, whether or not the apparentglobal increase in harmful algal blooms represents a real increase is a question that willprobably not be answered conclusively for some time to come. The growing interest in using coastal waters for aquaculture is leading to a greaterawareness of toxic algal species. People responsible for deciding quotas for pollutantloadings of coastal waters, or for managing agriculture and deforestation, should bemade aware that one probable outcome of allowing polluting chemicals to seep intothe environment will be an increase in harmful algal blooms. In countries that pridethemselves on having disease- and pollution-free aquaculture, every effort should bemade to quarantine sensitive aquaculture areas against the unintentional introductionof non-indigenous harmful algal species. Nor can any aquaculture industry affordnot to monitor for an increasing number of harmful algal species in water and for anincreasing number of algal toxins in seafood products using increasingly sophisticatedanalytical techniques such as LC-MS (see Section 3.2.5). Last, global climate change isadding a new level of uncertainty to many seafood safety monitoring programmes, asare range extensions of harmful algal bloom species through their being transportedin ships ballast water and as a consequence of increases in sea surface temperatures(Hallegraeff, 2010).

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