Harmful Algal Blooms and
- 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
- 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
- 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,
- 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
- 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
- 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
- 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
- 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
- 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 rapid changes and deterioration of many coastal
environments are being accompanied by a series of
harmful-and often unexpected-events involving marine
- Examples of the range of impacts and their potential
- 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
- 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
- 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
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