Euglena, sp. Is widespread and often abundant. Euglena sp reproduce rapidly and are especially common in warm seasons.They are commonly found in freshwater streams and ponds, when they may form a green scum on the surfaces of storages,irrigation bays or drainage ditches. They are green and sometimes red. They occasionally form green or red powdery films on the surface of ponds or dams. The surface colour can change from red to green in a few hours. Euglena is free swimming in ponds and lakes and is also found in mud rich in organic matter. There are 152 reported species 33 known to occur in Australia.
Microcystis, (Anacystis) is probably the most common toxic algae occuring in farm dams, usually form greenish-yellow bubbly masses in still or nearly still water. The plant cells are arranged like a small hair net. A blue green algae has numerous small cells crowded within a gelatinous matrix, forming a colony which may be ovate (like an egg) or an open meshwork. Microcystis is found free floating in lakes, reservoirs and sometimes in slow flowing rivers. Colour ranges from blue-green or yellowish brown. The colonies are usually globular. A hint of red can often be seen. It is a common cause of algal blooms and can secrete chemicals that inhibit other algae. It can also produce a polypeptide which is toxic to animals after drinking contaminated water. It has also been implicated in human illnesses including necrosis of the liver (after drinking) and severe dermatitis (after contact),etc. There are 40 reported species 7 known to occur in Australia.
Dictyosphaerium Anabaena, are a blue green species which grow in spirally coiled filaments, both species often occur as water blooms which can be concentrated by wind action. It is one of the toxic blooms forming blue green alga. It is coloured grey to blue-green or even green and is free floating in slow flowing or still waters. It sometimes forms a gelatinous mass. It most often occurs throughout late spring to autumn. Some species can produce an alkaloid (similar to cocaine) which acts as a neuromuscular blocking agent causing respiratory arrest, liver and gastro intestinal damage. It may also cause cancers. Species containing this alkaloid is highly toxic and animals may die soon after drinking water containing the toxin. Some blooms also cause contact irritation leading to severe dermatitis. There are approx. 70 species worldwide 29 occurring in Australia.
Nodularia is part of the Blue Green Algae (Cyanobacteria) family and is widespread. Blue greenish in colour. Usually found free floating in salt, brackish and freshwater lakes, dams and ponds. It is frequently intermingled with other algae forming extensive blooms. These blooms can cause death of stock or native animals. Nodularia produces hepatoxins that can kill liver cells, causing liver damage and gastro enteritis in humans. There are 12 known species one reported in Australia
Oscillatoria, is part of the Blue Green Algae (Cyanobacteria) family. It is blue greenish in colour, usually free floating, cylindrical or sometimes slightly tapering, unbranched filaments in aquatic environments. Some are tolerant of high levels of organic pollution and some are shade-tolerant and able to survive in water below blooms of green algae. It is implicated in irritation of skin and mucous membranes suffered by people swimming. It is widespread and common in a variety of habitats. There are approximately 150 known species of which 47 are known to occur in Australia. Some species causes contact irritation leading to severe dermatitis.
Spirogyra, very common green algae which feel like wet, soapy hair, bright green in colour often found free floating in static water near the surface or in masses in the sediment. Sometimes forms extensive mats in rivers, dams, ponds and often blocks channels. There are 300 known species 47 reported in Australia.
Chlorella, a small grass-green plant which usually stores starch.
Hydrodictyon, The plant cells are arranged like a small hair net. Usually found free floating in lakes, dams, ditches and slow flowing streams. It can become a real nuisance choking small streams and drains. There are 6 known species one reported in Australia.
Chara - dark grey-green with orange or green pinpoints on the branches. Chara often grows at the bottom of lakes in fresh and also some brackish waters one to six metres deep. Chara is common in freshwater areas with silty or sandy beds. It is usually more noticed in droughts when the water level drops. There are 19 known species 16 reported in Australia.
Nitella - thrive in water less alkaline than Chara. The plants are greener and are distinctly branched. Both are found in rice fields when the crop is thin. Similar to Chara. Nitella is common in freshwater areas with silty or sandy beds especially in clean water. It is green and found attached in sand and soil in still and flowing freshwater and occasionally in brackish waters. There are about 180 known species 24 reported in Australia. Mats of Nitella and Chara have a wiry, coarse texture as well as a slightly fishy odour.The common name for these algae is stonewort due to the very coarse, sandpapery feel to the mats.
Phormidium - Is widespread. It is blue greenish in colour usually attached to rocks, debris or sediment in fresh and salt water. Sometimes found on damp soil. The filaments form a consistent mass. Approx 49 species 20 reported in Australia.
Green algae range in size from microscopic to large plants, and canbe single celled, colonial, or filamentous. Some of the single celled and colonial green algae have small tails or "flagella" attached to each cell, which they use to swim. However many green algae are non-motile. Green algae may be either planktonic or attached. They show the greatest diversity of shapes, sizes and species of any group of freshwater algae. Green chloroplasts are frequently observable within the cells of green algae when looked at under a microscope.
Blue Green algae
Blue-green algae or Cyanobacteria are microscopic cells that grow naturally in Australian fresh and salt waters. They are a type of bacteria, but in some ways act like plants by using sunlight to manufacture carbohydrates from carbon dioxide and water, a process know as photosynthesis. In doing so, they release oxygen. They grow in dams, rivers, creeks, reservoirs, lakes and even hot springs. For information on specific species of blue green alga click here
When blue-green algae bloom, that is, grow to large numbers, they can form thick accumulations on the surface of the water. These accumulations are commonly known as scums. Blue-green algal scums form when large numbers of the algae float to the water surface using vesicles within their cells that they inflate with gas. Coming close to the surface enables them to gain maximum sunlight.
Water affected with blue-green algae usually smells and tastes unpleasant so that people are unlikely to drink it, however, take care to avoid skin contact, see the blue-green algae safety checklist for further details.
Blue-green algal blooms happen when there are high nutrient levels, low flows in rivers, low wind and high temperatures. There was a severe blue-green algal bloom over 1000 km long in the River system in October and November of 1991. This bloom impacted greatly on water supplies, agriculture, fish and aquatic animals, tourism and recreation.
Blue-green algae produce highly potent toxins
The main cause of concern about blue-green algae is the ability of some to produce highly potent toxins. There are four different forms of toxins that can be produced:
Toxic blue-green algae
The five main toxic blue-green algae in Australia are: Anabaena, Microcystis, Cylindrospermopsis, Oscillatoriaand Nodularia.
Anabaena, and Microcystis are the two main bloom-forming genera in Australian waters. Anabaena forms long chains of cells, called a trichome,(hair like structure) which sometimes grow in a spiral, depending on the species.
Microcystis aeruginosa is most common in lakes and reservoirs. It forms irregularly shaped colonies of cells up to 1 to 2 mm wide that can be visible to the naked eye. Microsystis blooms can be quite persistent lasting for months, or even years in some cases.
Oscillatoria is blue greenish in colour, usually free floating or entwined with other algae. It is widespread. There are approximately 150 known species of which 47 are known to occur in Australia. Some species causes contact irritation leading to severe dermatitis.
Irritant Blue-green algae
Not all blue-green algal species are toxic, and even different strains of the same species may differ, with some being highly toxic and others non-toxic. All blue-green algae however, contain lipopolysaccharides, which act as contact irritants, Even if the other more potent blue-green algal toxins are not present, the presence of these contact irritants may make the water unsuitable for body contact or recreation if the blue-green algae are present in bloom proportions. A number of other blue-green algae have been shown to be toxic overseas, but not yet so in Australia. Therefore these too should be treated with caution when present in bloom proportions.
Causes of algae Blooms
High nutrient load
Blue-green algal blooms are natural phenomena and while it is not exactly clear what triggers a bloom, excess human sources of nutrients such as fertilisers and sewage certainly can increase the intensity of blooms (i.e. greater number of algae).
One of the most important factors triggering blue-green algal blooms appears to be a lack of mixing of surface and deeper water layers in a river or reservoir. In lakes and reservoirs mixing is mainly controlled by wind and temperature. Through the summer months the surface waters heat up resulting in a warmer top layer and cooler bottom layer which do not mix. In rivers, mixing is mainly caused by flow. Flows from headwaters can decrease or stop during drought conditions allowing thermal stratification to develop. Weirs and extraction of water for irrigation and stock watering also reduce flow in rivers.
Algae float to surface
Some blue-green algae can float to the surface under these conditions having access to all the light in the top waters (photic region) and nutrients in the top and bottom waters. This allows the algae to flourish and bloom. Some other algae are motile and can swim to the photic region under these conditions.
Many other factors play a role in the formation of blue-green algal blooms including temperature, salinity, zooplankton grazing, pH and turbidity.
Strategies for preventing blue green algal blooms
The best way to so prevent algal blooms in farm dams or ponds is to reduce the amount of nutrients and sediments entering the dam.
Here are some ways to achieve this:
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