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Soil & Water Conservation Society of Metro Halifax (SWCSMH)
|April 10, 2015
Introduction and uniqueness
The algae are the simplest members of the
plant kingdom, and the blue-green algae are the simplest of the algae.
They have a considerable and increasing economic importance; they have
both beneficial and harmful effects on human life. Blue-greens are not
true algae. They have no nucleus, the structure that encloses the DNA,
and no chloroplast, the structure that encloses the photosynthetic
membranes, the structures that are evident in photosynthetic true
algae. Infact blue-greens are more akin to bacteria which have similar
biochemical and structural characteristics. The process of nitrogen
fixation and the occurrence of gas vesicles are especially important to
the success of nuisance species of blue-greens. The blue-greens are
widely distributed over land and water, often in environments where no
other vegetation can exist. Their fossils have been identified as over
three billion years old. They were probably the chief primary producers
of organic matter and the first organisms to release elemental oxygen, O2, into the primitive atmosphere, which was until then free from O2.
Thus blue-greens were most probably responsible for a major
evolutionary transformation leading to the development of aerobic
metabolism and to the subsequent rise of higher plant and animal forms.
They are referred to in literature by various names, chief among which
are Cyanophyta, Myxophyta, Cyanochloronta, Cyanobacteria, blue-green
algae, blue-green bacteria.
The majority of blue-greens are
aerobic photoautotrophs: their life processes require only oxygen,
light and inorganic substances. A species of Oscillatoria that is found
in mud at the bottom of the Thames, are able to live anaerobically.
They can live in extremes of temperatures -60°C to 85°C, and a few
species are halophilic or salt tolerant (as high as 27%, for
comparison, conc. of salt in seawater is 3%). Blue-greens can grow in
full sunlight and in almost complete darkness. hey are often the first
plants to colonize bare areas of rock and soil, as an example
subsequent to cataclysmic volcanic explosion (at Krakatoa, Indonesia in
1883). Unlike more advanced organisms, these need no substances that
have been preformed by other organisms.
At the onset of nitrogen limitation during
bloom conditions, certain cells in Anabaena and Aphanizomenon evolve
into heterocysts, which convert nitrogen gas into ammonium, which is
then distributed to the neighboring cells of a filament. In addition,
blue-greens that form symbiotic (mutually beneficial) relationships
with a wide range of other life forms, can convert nitrogen gas into
Finally, at the onset of adverse
environmental conditions, some blue-greens can develop a modified cell,
called an akinete. Akinetes
contain large reserves of carbohydrates, and owing to their density and
lack of gas vesicles, eventually settle to the lake bottom. They can
tolerate adverse conditions such as the complete drying of a pond or
the cold winter temperatures, and, as a consequence, akinetes serve as
"seeds" for the growth of juvenile filaments when favorable conditions
return. Heterocysts and akinetes are unique to the blue-greens.
Blue-greens in freshwater lakes
Unicellular and filamentous blue-greens are
almost invariably present in freshwater lakes frequently forming dense
planktonic populations or water blooms in eutrophic (nutrient rich)
waters. In temperate lakes there is a characteristic seasonal
succession of the bloom-forming species, due apparently to their
differing responses to the physical- chemical conditions created by
thermal stratification. Usually the filamentous forms (Anabaena
species, Aphanizomenon flos-aquae and Gloeotrichia echinulata) develop
first soon after the onset of stratification in late spring or early
summer, while the unicellular-colonial forms (like Microcystis species)
typically bloom in mid-summer or in autumn. The main factors which
appear to determine the development of planktonic populations are
light, temperature, pH, nutrient concentrations and the presence of
Attached and benthic populations in lakes
Many blue-greens grow attached on the
surface of rocks and stones (epilithic forms), on submerged plants
(epiphytic forms) or on the bottom sediments (epipelic forms, or the
benthos) of lakes.
The epilithic community displays a clearly
discernable zonation in lakes. Members of the genera Pleurocapsa,
Gloeocapsa and Phormidium often dominate the dark blue-black community
of the spray zone. Scytonema and Nostoc species form olive-green
coatings and are more frequent about the water line, whilst the
brownish Tolypothrix and Calothrix species are more typical components
of the subsurface littoral community.
The epiphytic flora of lakes is usually
dominated by diatoms and green algae, and blue-greens are of less
importance in this community. Species of the genera Nostoc, Lyngbya,
Chamaesiphon and Gloeotrichia have been occasionally encrusting
The epipelic community commonly includes
blue-greens like Aphanothece and Nostoc particularly in the more
eutrophic lakes. Benthic blue-greens growing over the littoral
sediments and on submerged plants may be responsible for the occasional
high rates of N2-fixation measured in oligotrophic lakes.
In the temperate region blue-greens are
especially common in calcareous and alkaline soils. Certain species,
Nostoc commune, are often
conspicuous on the soil surface. Acid soils, however, lack blue-green
element and are usually dominated by diatoms and green algae.
When viewed under the light microscope,
blue-greens show a variety of movements, such as gliding, rotation,
oscillation, jerking and flicking.
The formation of water blooms results from the redistribution and often
rapid accumulation of buoyant planktonic populations. When such
populations are subjected to suboptimal conditions, they respond by
increasing their buoyancy and move upward nearer to the water surface.
Water turbulence usually prevents them reaching the surface. If,
however, turbulence suddenly weakens on a calm summer day, the buoyant
population may 'over-float' and may become lodged right at the water
surface. There the cells are exposed to most unfavourable and dangerous
conditions, like O2 supersaturation, rapidly diminishing CO2
concentrations and intense solar radiation, which are inhibitory to
photosynthesis and N2-fixation, causing photo-oxidation of pigments and
inflicting irreversible damage to the genetic constitution of cells. A
frequent outcome of surface bloom formation is massive cell lysis and
rapid disintegration of large planktonic populations. his is closely
followed by an equally rapid increase in bacterial numbers, and in turn
by a fast deoxygenation of surface waters which could be detrimental to
animal populations within the lake. Water blooms are objectionable for
recreational activities, and more importantly, create great nuisance in
the management of water reservoirs.
Most of these conditions are produced by just three blue-greens, informally referred to as Annie (Anabaena flos-aquae), Fannie (Aphanizomenon flos-aquae) and Mike (Microcystis aeroginosa).
An oversupply of nutrients, especially phosphorus and possibly
nitrogen, will often result in excessive growth of blue-greens because
they possess certain adaptations that enable them to outcompete true
algae. Perhaps the most important adaptation is their positive
buoyancy, which is regulated by their gas vesicles which are absent in
Their reputation as "nuisance" or "noxious"
is totally undeserved. While periodic blooms are considered a nuisance
in recreational lakes and water supply reservoirs of North America, the
near continuous blooms of blue-greens in some tropical lakes are a
valuable source of food for humans. Some blue-green species make major
contributions to the world food supply by naturally fertilizing soils
and rice paddies. R.N. Singh of the Banares Hindu University in India
has shown that the introduction of blue-green algae to saline and
alkaline soils in the state of Uttar Pradesh increases the soils'
content of nitrogen and organic matter and also their capacity for
holding water. This treatment has enabled formerly barren soils to grow
crops. Astushi Watanabe of the University of Tokyo found the
introduction of Tolypothrix tenuis resulted in a 20% increase of rice
crop. W.E. Booth of the University of Kansas showed through experiments
in Kansas, Oklahoma and Texas, that a coating of blue-greens on prairie
soil binds the particles of the soil to their mucilage coating,
maintains a high water content and reduces erosion.
Humans also consume Spirulina. It
contains all of the amino acids essential for humans, and its protein
content is high (± 60%). It is a staple food in parts of Africa and
Mexico. In China, Taiwan and Japan, several blue-greens are served as a
side dish and a delicacy. Several areas in North America culture and
commercially process certain blue-greens for various food and medicinal
products such as vitamins, drug compounds, and growth factors.
Heterocystous blue-greens possess the unique ability to simultaneously evolve O2 in photosynthesis (in vegetative cells) and H2 by nitrogenase catalyzed electron transfer to H+-ions (in heterocysts), in the absence of N2
or other substrates of nitrogenase. This is the basis for the attempts
of several workers to exploit the potential through the development of
a `biophotolytic system' for solar energy conversion, even though to
date the thermodynamic efficiency has been disappointingly low.
utilization of blue-greens in food production and in solar energy
conversion may hold immense potential for the future, and could be
exploited for man's economy. Progress in the study of the genetics of
blue-greens may enable us to manipulate the N2-fixation (nif) and associated genes, and produce strains which fix N2, evolve H2 or release ammonia with great efficiency.
(Also see, Diverse taxa of cyanobacteria produce ß-N-methylamino-L-alanine (BMAA), a neurotoxic amino acid- Proc. the National Academy of Sciences of the USA, 2005)
|Poisonous blue-greens occur in ponds and lakes
throughout the world. In Canada, they primarily occur in the prairie
provinces. Poisoning has caused the death of cows, dogs, and other
animals. Although humans ordinarily avoid drinking water that displays
a blue-green bloom or scum, they may be affected by toxic strains when
they swim or ski in recreational water bodies during a bloom. Typical
symptoms include redness of the skin and itching around the eyes; sore,
red throat; headache; diarrhea; vomiting; and nausea. The frequently
occurring `swimmers itch' is attributed to contact with Lyngbya majuscula, Schizothrix calcicola and Oscillatoria nigroviridis,
which are commonly found in tropical and subtropical seawaters. The
toxins responsible are lipid-soluble phenolic compounds. Since the same
or similar symptoms can be produced by bacteria or viruses, one should
not necessarily conclude that blue-greens are responsible for a human
illness simply because the sick individual recently swam in a lake or
pond that has suffered a bloom. Human death has not been documented.
Reported cases affecting humans list Anabaena as the main culprit.
Most of the recorded toxic blooms are caused by Microcystis aeruginosa,
which manufactures "microcystin", which yields 7 (or 14) amino acids
upon hydrolysis. It causes enlargement and congestion of the liver
followed by necrosis and haemorrhage, and may also exhibit neurotoxic
But many toxic blooms are also produced by either Anabaena flos-aquae (manufactures "anatoxins") or Aphanizomenon flos-aquae (manufactures "aphantoxins").
Alkaloid toxins (anatoxins, aphantoxins) act on the nervous system, leading to paralysis of muscles needed for breathing.
Two other genera, Oscillatoria and Nodularia
are also known to produce toxic populations. Whether the animal
survives the poisoning depends primarily upon the concentration of
toxin ingested. Blue-green toxins may act on zooplankton and might be
an effective mechanism of protection against grazing pressures.
Little is known about the percent of blooms that are toxic
(upto 25% quoted in literature), and also why a toxic population is
produced. A complicating factor is that part of a bloom can be toxic
and another part nontoxic within the same lake. It has been suggested
that toxic strains may develop only under a particular set of
environmental conditions, or that toxin production may be associated
with plasmid-mediated gene transfer.
Colour and identification
The blue-green color of cells (cyan means
blue-green) is due to the combination of green chlorophyll pigment and
a unique blue pigment (phycocyanin). However, not all blue-greens are
blue-green. Their pigmentation includes yellow-green, green,
grey-green, grey-black, and even red specimens. The Red Sea derives its
name from occasional blooms of a species of Oscillatoria
that produces large quantities of a unique pigment called
phycoerythrin. In the arid regions of Central and East Africa,
flamingos consume vast quantities of Spirulina, and their feathers derive their pink color from carotene pigments in filaments of Spirulina.
The blue-greens are microscopic life forms
that exhibit several different types of organization. Some grow as
single cells enclosed in a sheath of slime-like material, or mucilage.
The cells of others aggregate into colonies that are either flattened,
cubed, rounded, or elongated into filaments. Actual identification of
cyanobacteria (blue-greens) requires microscopic examination of cells,
colonies, or filaments, although experienced aquatic biologists can
usually recognize Microcystis (colonies look like tiny grey-green clumps) and Aphanizomenon (green, fingernail-like or grass-like clippings).
Measures to control the growth of blue-greens
Chemicals are widely used to prevent the
growth of nuisance algae, and the commonest one being copper sulphate.
A number of other algicides are phenolic compounds, amide derivatives,
quaternary ammonium compounds and quinone derivatives. Dichloron
aphthoquinone is selectively toxic to blue-greens. The hazards of using
toxic chemicals indiscriminately in the natural environment are well
Biological control is in principle possible,
though not always practical and as effective. Invertebrates like
cladocerans, copepods, ostracods and snails are known to graze on green
algae and diatoms. Daphnia pulex has been reported to feed on Aphanizomenon flos-aquae while present in the form of single filaments or small colonies but avoid large raft-like colonies. The copepod Diaptomus has been implicated in the grazing of Anabaena populations in Severson Lake, Minnesota.
Micro-organisms (fungi, bacteria and
viruses) appear to play an important part in regulating growth of
blue-greens in freshwaters. Certain chytrids (fungal pathogens)
specifically infest akinetes, other heterocysts. Bacterial pathogens
belonging to the group of Myxobacteriales can effect rapid lysis of a
wide range of unicellular and filamentous blue-greens, though
heterocysts and akinetes remain generally unaffected. Viral pathogens
belonging to the group of cyanophages exhibit some degree of host
specifity. Phage AR-1 attacks Anabaenopsis, phages SM-1 and AS-1 are effective against the unicellular forms, Synechococcus and Microcystis, Phage C-1 lyses Cylindropermum, and the LPP-1 virus is effective against strains of Lyngbya, Phormidium and Plectonema.
The long-term approach is no doubt the systematic removal of major nutrients.
- Canadian Council of Ministers of the Environment. Updated 1992. Canadian Water Quality Guidelines. Environment Canada.
- Carmichael, W.W., and L.D. Schwartz. 1984. Preventing
Livestock Deaths from Blue-Green Algae Poisoning. U.S. Dept. of Ag.,
Farmer's Bull. no. 2275. 11pp.
- Carmichael, W.W. 1991. Blue-Green Algae: An Overlooked Health Threat. In Health & Environment Digest, Freshwater Foundation. July, 1991. 5(6):1-4.
- Carmichael, W.W. 1992. A Review, Cyanobacteria secondary metabolites- the cyanotoxins. In J. Applied Bacteriology. 72:445-459.
- Carmichael, W.W. 1992. A Status Report on Planktonic
Cyanobacteria (Blue-Green Algae) and Their Toxins. USEPA
#EPA/600/R-92/079. 141pp. (includes 867 references)
- Echlin, P. 1966. The Blue-Green Algae. Scientific American, 214(6):74-81.
- Fay, P. 1983. The Blue-greens (Cyanophyta- Cyanobacteria). Edward Arnold (Pubs.), Baltimore, MD. 88pp.
- Haynes, R.C. 1988. Deptt of Env. Qual. Engg.,
Commonwealth of Massachusetts. An Introduction to the Blue-Green Algae
(Cyanobacteria) with an Emphasis on Nuisance Species. North Am. Lake
Manage. Soc. 19pp.
- Lambou, V.W., F.A. Morris, R.W. Thomas, M.K. Morris,
L.R. Williams, W.D., Taylor, F.A. Hiatt, S.C. Hern, and J.W. Hilgert.
1977. Distribution of phytoplankton in West Virginia lakes. Working
Paper No. 693, National Eutrophication Survey, USEPA. 23pp.
- Needham, J.G., and P.R. Needham. 1964. A guide to the
study of Fresh-Water Biology. 5th Ed. Holden-Day, Inc., San Francisco,
- Nishiwaki-Matsushima, R., T. Ohta, S. Nishiwaki, M.
Suganuma, K. Kohyama, T. Ishikawa, W.W. Carmichael, and H. Fujiki.
1992. Liver tumor promotion by the cyano- bacterial cyclic peptide
toxin microcystin-LR. In J. Cancer Res. Clin. Oncol, Springer-Verlag. 118:420-424.
- Soil & Water Conservation Society of Metro Halifax. 1992. Phytoplankton assemblages in six Halifax County lakes. 56p.
- Soil & Water Conservation Society of Metro Halifax.
1993. Phytoplankton Assemblages in 21 Halifax Metro Lakes (Phase-B3
Limnology project), November 1993. 130p.
- Soil & Water Conservation Society of Metro Halifax. 1993. Synopsis titled "Phytoplankton" (of fresh waters). 11p.
- Wedepohl, R.E., D.R. Knauer, G.B. Wolbert, H. Olem,
P.J. Garrison, and K. Kepford. 1990. Monitoring Lake and Reservoir
Restoration. EPA 440/4-90-007. Prep. by N. Am. Lake Manage. Soc. for
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