Harmful Algal Blooms
From time to time, usually in late summer, great masses
of harmful marine
dinoflagellates can accumulate in dense
visible patches called Harmful Algal Blooms HAB in coastal regions. The
dinoflagellates produce potent toxins that accumulate in marine animals.
Left: A massive “red
bloom of the dinoflagellate Noctiluca scintillans in the North
Sea near the Skagerrak in early August 2001.
From The Baltic
Sea Portal (Itameriportaali).
Right: Noctiluca scintillans.
Unfortunately, a small number of species produce potent
neurotoxins that can be transfered through the food web where they
affect and even kill the higher forms of life such as zooplankton,
shellfish, fish, birds, marine mammals, and even humans that feed either
directly or indirectly on them.
Algae and Red Tides Primer
Marine biotoxins, produced by
phytoplankton usually during harmful algal blooms, are
some of the most potent toxins in the world and extremely dangerous.
For some toxins, doses at the microgram per kilogram level are more
than sufficient to kill. When enough toxin is accumulated in fish
or shellfish, small amounts of cooked or raw tissue can kill a human.
For example, recorded harmful algal blooms have produced enough paralytic
shellfish poisoning PSP toxin in mussels that the consumption of
one or two small mussels could have killed a normal, healthy adult
human. While some toxins are very potent, i.e., requiring only small
amounts to produce illness or death, other less potent toxins may
accumulate to such high levels that they still can cause harm. For
example, the total dose of domoic acid to produce a minimal toxic
effect is fairly high (i.e., tens of milligrams) but it can accumulate
in sufficient quantities in shellfish to produce deadly results (ranging
from mild stomach distress to permanent brain damage and even death).
Northwest Fisheries Science Center Harmful Algal Blooms Page.
- They kill fish, birds, mammals.
- They cause illness and sometimes
lead to death when people eat shellfish or fish that have concentrated
the nerve poisons produced by the blooms. The most common symptoms
include nausea, vomiting, abdominal cramps, diarrhea, and neurological
disorders. The specific illnesses are (from Harmful
Algae, Woods Hole
Shellfish Poisoning (ASP) is caused by species of the diatom
which produce the toxin domoic acid. The toxin is concentrated by
mussels, scallops, clams, and crabs. The blooms cause health problems
along the US west coast and New England.
Amnesic Shellfish Poisoning (ASP) can be
a life-threatening syndrome that is characterized by both gastrointestinal
and neurological disorders. Gastroenteritis usually develops within
24 hours of the consumption of toxic shellfish; symptoms include
nausea, vomiting, abdominal cramps, and diarrhea. In severe cases,
neurological symptoms also appear, usually within 48 hours of toxic
shellfish consumption. These symptoms include dizziness, headache,
seizures, disorientation, short-term memory loss, respiratory difficulty,
and coma. From Amnesic
Shellfish Poisoning, Harmful Algae, Woods Hole Oceanographic Institution.
Fish Poisoning (CFP) is caused by the dinoflagellate Gambierdiscus
toxicus, which produces ciguatoxin and maitotoxin, some of
the most lethal natural toxins known. It causes health problems
in tropical waters, including Hawai'i, the Gulf of Mexico, and Puerto
Ciguatera Fish Poisoning (CFP) produces
gastrointestinal, neurological, and cardiovascular symptoms. Generally,
gastrointestinal symptorms such as diarrhea, vomiting, and abdominal
pain occur first, followed by neurological dysfunction including
reversal of temperature sensation, muscular aches, dizziness, anxiety,
sweating, and a numbness and tingling of the mouth and digits. Paralysis
and death have been documented, but symptoms are usually less severe
although debilitating (Miller, 1991). From Ciguatera
Fish Poisoning, Harmful Algae, Woods Hole
Shellfish Poisoning (DSP) is caused by the dinoflagellates
Prorocentrum lima and species of the genus Dinophysis, which produce
the toxins okadaic acid, dinophysiotoxin. It causes health problems
along the Atlantic coast of Canada.
Diarrhetic Shellfish Poisoning (DSP) produces
gastrointestinal symptoms, usually beginning within 30 minutes to
a few hours after consumption of toxic shellfish (Yasumoto and Murato,
1990). The illness, which is not fatal, is characterized by incapacitating
diarrhea, nausea, vomiting, abdominal cramps, and chills. From Diarrhetic
Shellfish Poisoning, Harmful Algae, Woods Hole
Shellfish Poisoning (NSP) is caused by dinoflagellates of
the genus Karenia, especially Karenia
brevis, which secrete brevetoxins. It causes health problems
around the Gulf of Mexico.
Neurotoxic Shellfish Poisoning (NSP) produces an intoxication syndrome
nearly identical to that of ciguatera in which gastrointestinal and
neurological symptoms predominate. In addition, formation of toxic
aerosols by wave action can produce respiratory asthma-like symptoms.
No deaths have been reported and the syndrome is less severe than
ciguatera, but nevertheless debilitating. From Neurotoxic
Shellfish Poisoning, Harmful Algae, Woods Hole
Shellfish Poisoning (PSP) is caused by various dinoflagellates
including species of Alexandrium, Gymnodinium
catenatum, and Pyrodinium
bahamense, which produce saxitoxin. It causes health problems
along the US west coast from Alaska to California, Hawai'i, and in
Paralytic Shellfish Poisoning (PSP), like
ASP, is a life threatening syndrome. Symptoms are purely neurological
and their onset is rapid. Duration of effects is a few days in non-lethal
cases. Symptoms include tingling, numbness, and burning of the perioral
region, ataxia, giddiness, drowsiness, fever, rash, and staggering.
The most severe cases result in respiratory arrest within 24 hours
of consumption of the toxic shellfish. From Paralytic
Shellfish Poisoning, Harmful Algae, Woods
Hole Oceanographic Institution.
- Although not a danger, some
harmful algal blooms produce beautiful displays of bioluminescence when
disturbed at night, especially by breaking waves.
- Recently a new organism, Pfeisteria,
has been in the news because of its impact on some east coast estuaries. It
is associated with fish kills and ulcers, and with some illnesses. The
organism, its toxins, and health influences are not yet well known.
Hundreds, sometimes thousands
of dead fish, their bodies disfigured by bizarre open sores--these
were the press reports out of eastern North Carolina in the early
Nineties. Baffled scientists tested for the usual fish kill suspects
and found none ... In Maryland, a family of people working on the
water reported they suffered "shortness of breath, nausea,
leg sores and even memory loss," and a local doctor treated
a man who "suffered a severe headache and 30 lesions after
water-skiing in the lower Pocomoke for a half-hour." Doctors
from the Johns Hopkins and University of Maryland medical schools
examined a number of these people and concluded that pfiesteria
toxins were the most likely cause of their illnesses.
for Mathematics and Science Education
Pfiesteria-related lesions on fish.
From Environmental Protection Agency Pfiesteria Page
single-celled, mostly photosynthetic organisms with a nucleus (eukaroyotes).
They have hairlike flagella which they use to swim through the water.
To learn more about dinoflagellates,
see the Tree of Life,
then Eukaryotes (organisms
with a cell nucleus), then Alveolates.
The Asian Natural
Environmental Science Center at the University
of Tokyo, Japan, in cooperation with the Intergovernmental Oceaonographic
Commission's Science and Communication Centre on Harmful Algae, University
of Copenhagen, Denmark, has posted photographs of
many organisms that cause harmful algal blooms in the Pacific.
Causes of Blooms and Dead Zones
- Increase in nutrients. The rapid increase of population in coastal
zones and the increased use of fertilize on farms and lawns leading
to more nutrients in runoff to the ocean may be contributing to increased
- Over fishing is an important contributor to the recent
increase in toxic algal blooms and ocean dead zones. Jackson, in his
2001 Science article of on Historical Over fishing
and the Recent Collapse of Coastal Ecosystems finds that:
There are three important corollaries
to the primacy of overfishing... The first is that pollution, eutrophication,
physical destruction of habitats, outbreaks of disease, invasions
of introduced species, and human-induced climate change all come
much later than overfishing in the standard sequence of historical
events... The second important corollary is that overfishing may
often be a necessary precondition for eutrophication, outbreaks of
disease, or species introductions to occur... The third important
corollary is that changes in climate are unlikely to be the primary
reason for microbial outbreaks and disease... Ecological extinction
of entire trophic levels makes ecosystems more vulnerable to other
natural and human disturbances such as nutrient loading and eutrophication,
hypoxia, disease, storms, and climate change... This is perhaps
most apparent in the rise of eutrophication, hypoxia, and the outbreak
of toxic blooms and disease following the destruction of oyster reefs
by mechanical harvesting of oysters.
Most recent changes to coastal marine ecosystems subsequent to overfishing
involve population explosions of microbes responsible for increasing
eutrophication (74-76, 81), diseases of marine species (104), toxic
blooms (82, 83), and even diseases such as cholera that affect human
health (104, 105). Chesapeake Bay (81) and the Baltic Sea (74) are
now bacterially dominated ecosystems with a trophic structure totally
different from that of a century ago. Microbial domination also has
expanded to the open ocean off the mouth of the Mississippi River (106)
and to the Adriatic Sea (107).
Nowhere is the lack of historical perspective more damaging to scientific
understanding than for microbial outbreaks. Plans for remediation of
eutrophication of estuaries are still based on the belief that eutrophication
is caused only by increased nutrients without regard to overfishing
of suspension feeders. Even more remarkable is the attribution of the
rise in marine diseases to climate change and pollution (104) without
regard to the pervasive removal of higher trophic levels and the asynchronous
outbreaks of disease in different ecosystems that belie a simple climatic
From Jackson et al (2001).
The number of harmful algal blooms has increased over the last 40 years,
especially in regions with large increases in coastal populations and
From Harmful Algal Bloom project, Woods Hole Oceanographic Institution.
Maps of Observed Blooms
and North America (Drag handle on bottom right of pop-up maps
to enlarge map so it is legible).
Location where Paralytic Shellfish Poisoning toxins were
found in Europe 1993-2002.
- USA and World
maps from the Harmful Algae web pages of the Woods
Hole Oceanographic Institution.
Maps of both historical and real-time data
- Texas Information
Learn More About Harmful Algal Blooms
To learn more about these blooms, read harmful
algal and Harmful
Algae pages produced by the Woods Hole Oceanographic Institution.
Then read Introduction
to Ecology and Oceanography of Harmful Algal Blooms. You may also
wish to scan some of the information at the Bigelow
Lab's site. But be warned. If you do, you may never again want
to eat fish.
Anderson, Donald M. 2004. The Growing Problem
of Harmful Algae. Oceanus 43 (2): 1–5.
Jackson, J. B. C., M. X. Kirby, et al. (2001). Historical
Overfishing and the Recent Collapse of Coastal Ecosystems. Science 293
3 August, 2009