A REVIEW OF HARMFUL ALGAL BLOOMS AND THEIR APPARENT GLOBAL INCREASE

In some situations algal blooms can have detrimental consequences to aquaculture, fisheries and tourism, with major economic, environmental and human health problems. Some 300 of the 5000 known species of marine phytoplankton can at times occur in such high numbers that they discolour the sea (red tides) and 40 or so species can produce toxins that can find their way though fish and shellfish to humans. While blooms are natural phenomena, much recent human activity has heightened the intensity, frequency and distribution of such algal growths. Comments are made on diarrhetic shellfish poisoning and amnesic shellfish poisoning. The consequences of the increased use of coastal waters for mariculture are noted, and the increase of algal blooms by cultural eutrophication is stressed, with particular reference to ciguatera fish-food poisoning and coral reef distribution. Stimulation of algal blooms by unusual climatic conditions are noted, with reference to toxic Pyrodinium bahamense blooms in the tropical Indo-West Pacific and fossil blooms of Gymnodinium catenatum in the Kattegat-Skagerrak. Notes are also given on the transport of dinoflagellate cysts in ships' ballast water or associated with the transfer of shellfish stock. -P.J.Jarvis