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Harmful Algal Blooms and Toxins

The Problem

  • There are some 4,000 known species of microscopic algae, called microalgae or phytoplankton, in the global ocean. Approximately 300 of these have been identified with periodic explosions of growth, in what amounts to extensive monocultures of the particular species involved. Dense growths of microalgae are broadly termed "blooms."
  • While single species blooms can turn the water surface red, brown, yellow, green or white, they are often generically referred to as "red tides" and are often associated with harmful or toxic effects. When the blooming microalgae have properties that are deemed harmful to humans or other life, the blooms are called Harmful Algal Blooms, or HABs.
  • In recent years, there has been growing alarm over what appears to he an "epidemic" of HABs worldwide.
  • In many regions, HABs are occurring more frequently' occurring over larger areas and lasting longer: HABs are also being recorded in areas where previously they were not known. In other cases, algal species previously benign, or even unknown, have suddenly emerged to become problematic.
  • HABs can kill marine life and cause losses to aquaculture operations. A number of species release powerful toxins that can make their way through the food web to affect seabirds, marine mammals and humans, sometimes fatally.
  • Some toxic species can cause a variety of human ailments, contracted either through inhaling airborne toxins, skin contact or, more commonly, eating contaminated shellfish. These toxins may cause amnesia, stomach cramps, nausea, memory loss, paralysis and even death.
  • Not all HABs are toxic. Only forty or so species are believed to produce such potent toxins. Some species are merely unpalatable to other marine life because of gelatinous envelopes or other characteristics and they exact their harmful effects by essentially "starving" the food chain. Other species can cause physical damage, as the blooms of species which contain barbs that lodge among gill tissues of fish, causing death. Such blooms can cause a great deal of financial damage by killing farmed fish, which are grown in crowded aquaculture pens.
  • Some blooms of algae are not inherently harmful but may result in severe environmental impacts. For instance, low oxygen conditions may result from the decay of excessive amounts of algal growth caused by nutrient pollution.

The Causes

  • Although there are some scientists who believe the increase in reports of HABs is a function of increased awareness and monitoring, others have provided compelling evidence that, for some regions, human activities play an important role.
  • The primary human contribution to HABs is thought to be nutrient pollution -- from, amongst other things, agriculture, sewage outfalls and mining -- creating a more favorable, nutrient-rich environment in coastal waters in which certain groups of phytoplankton can thrive.
  • Climate change may also be making some coastal environments more hospitable to harmful phytoplankton species.
  • Many species of phytoplankton are also transported around the world in ships' ballast water and discharged in areas where they did not previously occur. Others are distributed accidentally through the transfer of shellfish for aquaculture.

The Context

  • The rapid changes and deterioration of many coastal environments are being accompanied by a series of harmful-and often unexpected-events involving marine phytoplankton.
  • Examples of the range of impacts and their potential seriousness include:
    • The initiation of recent cholera epidemics in South America; cholera bacteria thrive in zooplankton blooms, which are stimulated by algal blooms, where they are then widely available to be vectored into seafood and drinking water.
    • The recent emergence of Pfiesteria, the tiny "ambush predator"; this species has caused massive fish kills and human illness in North Carolina, and has recently become a problem in Maryland.
    • The death of 4 people and the hospitalization of over a hundred more in 1987 in eastern Canada when they consumed mussels contaminated with a previously undescribed toxin.
    • The death of over 150 endangered manatees in Florida in 1996; a "red tide" of the species Karenia brevis, which produces brevetoxin was considered the cause.
    • Of great importance may be the effects associated with climate change; changes in upwelling patterns and other hydrological features, and increases in water temperature, may stimulate bloom formation or expand the range of noxious and harmful species.

Further Reading

Anderson, D. M., Glibert, P. M., and Burkholder, J. M.  Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences.  Estuaries 25(4B): 704-726, 2002.

Beman, J.M., Arrigo, K.R., and Matson, P.A.  Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean.  Nature 434(7030): 211-214, 2005.

Brand, L.E. and Compton, A.  Long-term increase in Karenia brevis abundance along the Southwest Florida Coast.  Harmful Algae 6(2): 232-252, 2007.

Edwards, M., Johns, D.G., Leterme, S.C., Svendsen, E., and Richardson, A.J.  Regional climate change and harmful algal blooms in the northeast Atlantic.  Limnology and Oceanography 51(2): 820-829, 2006.

Glibert, P.M., Anderson, D.M., Gentien, P., Granéli, E., and Sellner, K.G.  The global, complex phenomena of harmful algal blooms.   Oceanography 18(2): 136-147, 2005.

Glibert, P.M., Seitzinger, S., Heil, C.A., Burkholder, J.M., Parrow, M.W., Codispoti, L.A., and Kelly, V.  The role of eutrophication in the global proliferation of harmful algal blooms.  Oceanography 18(2): 198-209, 2005.

Glibert, P.M., Harrison, J., Heil, C., and Seitzinger, S.  Escalating worldwide use of urea - a global change contributing to coastal eutrophication.  Biogeochemistry 77(3): 441-463, 2006.

Heil, C.A., Glibert, P.M., and Fan, C.  Prorocentrum minimum (Pavillard) Schiller: A review of a harmful algal bloom species of growing worldwide importance.  Harmful Algae 4(3): 449-470, 2005.

Hoagland, P. and Scatasta, S.  2006.  The economic effects of harmful algal blooms.  Pages 391-402 in Ecological Studies 189: Ecology of Harmful Algae (E. Graneli and J.T. Turner, eds.).
Springer-Verlag, Berlin.

Landsberg, J., Van Dolah, F., and Doucette, G.  2006.  Marine and estuarine harmful algal blooms: Impacts on human and animal health.  Pages 165-215 in Oceans and Health: Pathogens in the Marine Environment (S. Belkin and R.R. Colwell, eds.).  Springer, New York.

Larkin, S.L. and Adams, C.M.  Harmful algal blooms and coastal business: economic consequences in Florida.  Society and Natural Resources 20(9): 849-859, 2007.

Scavia, D. and Bricker, S.B.  Coastal eutrophication assessment in the United States.  Biogeochemistry 79(1-2): 187-208, 2006.

Smayda, T.J.  Reflections on the ballast water dispersal - harmful algal bloom paradigm.  Harmful Algae 6(4): 601-622, 2007.