As currently these reserves are declining, we are again looking at the potential of photosynthesis to re capture inorganic carbon and convert it into the organic molecules that are the feedstock of all carbon based food and fuel available today. Microalgae and cyanobacteria have great potential as a photosynthetic catalyst as they have some important advantages over traditional agricultural crops. For example, the predicted areal productivities of microalgae are much higher and can be obtained without the use of arable land.
Many algal species are salt tolerant and therefore sea water can be used for cultivation. Microalgae, also called phytoplankton by biologists, are very small plant-like organisms between micrometres in diameter without roots or leaves.
They often exhibit population explosions and abrupt die-offs, also resulting in oxygen deficits. Apart from killing aquatic life indirectly through oxygen depletion, blue-green algae-and some other types of algae as well-can cause more direct harm.
While some blue-greens are currently being touted for their nutritional benefits and medicinal value in health food markets, other varieties are known to be poisonous to fish, animals, and humans through toxic impacts on the nervous system, skin, respiratory tract and liver. Occasional livestock losses are attributable to blue-green toxins in stock ponds, and some people may have extreme allergic reactions to toxins produced by these algae. In marine waters, fish, manatees, sea lions, dolphins, whales, pelicans, and many other forms of wildlife are targets of other toxic algae.
One widespread group is known as the dinoflagellates. Although they generally fall under the broad heading of "algae," dinoflagellates are single-celled organisms with characteristics somewhere between those of plants and animals, belonging in a group scientists call the "protists.
Toxins produced within these microorganisms can become concentrated by animals that feed on them, such as shellfish and other filter-feeders.
This "bioconcentration" can affect humans if contaminated shellfish are accidentally consumed. Monitoring programs and regular shellfish inspections, however, generally prevent such occurrences. Toxins can also be released directly into the environment when a dinoflagellate bloom dies back.
An estimated 14 million fish were killed during a red tide outbreak in Texas in September and October Airborne toxins in sea spray can irritate the eyes and respiratory systems of humans.
Noxious dinoflagellate blooms appear to be occurring more frequently in poorly flushed bays and lagoons in many parts of the world, although some have been occurring regularly for hundreds of years. Like all green plants, algae produce oxygen during the daylight hours as a by-product of photosynthesis. This is usually a major source of oxygen in fish ponds. In darkness, however, all plants consume oxygen, including algae. Algae blooms in natural water bodies or fish ponds normally produce much more oxygen in the daylight than they consume during the night, but some situations reduce the amount of oxygen a bloom produces without reducing its nighttime oxygen consumption.
Trace minerals or nutrients needed by the algae are occasionally used up, causing some or even all, of the bloom to die back temporarily. The resulting bacterial decomposition and loss of normal oxygen production can lead to oxygen depletions and fish kills. Pond water generally changes from a deep green to black, gray, brown or clear after a phytoplankton die-off.
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