ABSTRACT
The microscopic planktonic algae of the world’s oceans provide critical ecosystem services in terms of food for fi lter-feeding bivalve shellfi sh and larvae of crustaceans and fi nfi sh, but also as drivers of global climate (46% of global photosynthesis). In most cases, the proliferation of plankton algae (so-called ‘algal blooms’; up to millions of cells per litre) therefore is benefi cial to humankind. However, in some situations algal blooms can have a negative effect, causing severe economic losses to aquaculture, fi sheries and tourism and having major environmental and human health impacts. Among the 5,000 species of living marine phytoplankton, some 300 species can at times occur in such high numbers that they discolour the surface of the sea, while 80 or so species have the capacity to produce potent toxins. The Harmful Algal Bloom (HAB) designation is a societal concept rather than scientifi c defi nition-blooms are considered to fi t the HAB criterion if they cause injury to human health or socioeconomic interests (Table 1; Hallegraeff 1993). Some nontoxic HABs (e.g., Noctiluca, Trichodesmium)
Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia. Email: Hallegraeff@utas.edu.au
cause damage to ecosystems, fi shery resources and recreational facilities, due to the high biomass of accumulated algae, which can create noxious scums and foam, shade other phytoplankton and sea grass beds, and cause indiscriminate marine faunal mortalities via decay and oxygen depletion. Other HAB species (e.g., Chattonella, Cochlodinium, Heterosigma, Karenia, Karlodinium) can release compounds that are, strictly speaking, not toxins [e.g., reactive oxygen species (ROS), polyunsaturated fatty acids (PUFAs), mucilage] but can be injurious and even lethal to fi nfi sh, especially when held captive in aquaculture operations (US$500M loss in the Seto Inland Sea in 1972, US$95M loss in Korea in 1995, Okaichi 1989). Of most concern are HAB species that are toxigenic and produce blooms that cause illness and death of fi sh, seabirds, mammals (whales, porpoises, manatees, sealions) and other marine life, often via toxin transfer through the food web (Scholin et al. 2000). Human consumers of seafood contaminated by these toxins may be poisoned, suffering acute toxic symptoms and even fatalities in extreme cases. On a global scale, close to 2,000 cases of human poisoning
Table 1. Different types of harmful algal bloom.
