Dinoflagellates account for about 75% (45-60 taxa) of all algal species forming harmful algal blooms, or HABs (Smayda 1997). HABs have often been referred to as "red tides". This term can be quite misleading, however, given that many toxic blooms occur when waters are not discolored and, conversely, blooms may occur in which the high biomass and pigments of the dinoflagellates turn the water red yet they are not toxic (Hackett et al. 2004). Dinoflagellate toxins may have serious negative impacts on a wide variety of animals exposed to them.

Consumption of seafood (shellfish or fish) contaminated by algal toxins may result in a variety of seafood poisoning syndromes in humans, including among others paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), diarrheic shellfish poisoning (DSP), ciguatera fish poisoning (CFP) and azaspiracid shellfish poisoning (ASP) (Hackett et al. 2004; Wang 2008). Most of these poisonings are caused by neurotoxins which present themselves with highly specific effects on the nervous systems of animals, including humans, by interfering with nerve impulse transmission.

PSP, which is caused by blooms of dinoflagellates belonging to several different genera, is probably the most widespread of the HAB poisoning syndromes. It may result in human illness and death, loss of seafood resources, reduced tourism and recreational activities, alteration of local marine ecosystems, and death of marine mammals, fish, and seabirds (Hackett et al. 2004).

Although the impact of HABs is mainly negative, Camacho et al (2007) review some of the potential medical applications of dinoflagellate toxins, as well as the challenges in pursuing research on them.