Introduction to Algal Habitats and Distribution:

Algae range from unicellular (microscopic) to large (macroscopic) thalloid forms developing in range of habitats roughly all over surface of earth. Wherever there is water, slight moisture or water vapors, and though feeble, they are certain to emerge as yellow, green, or patches that in course of time cover whole surface. Their occurrence and development is handled by many factors and is subject of science, ecology. When numerous kinds of algae grow together in similar natural circumstances they are known as communities. Composition of the community is found out by physical and chemical nature of habitat. In several cases algal community indicates nature of habitat, whether it is rich or poor in nutrients or polluted etc, or is serves as ecological indicator.

Aquatic Algae:

Many algae grow in water in absence of which they quickly dry up and die; though, there are also subaerial algae. Depending in concentration of salts there are diverse types of water bodies like brackish water, fresh water, brine-salt lakes, sea water, and salt pans. Further, these habitats these days may have several kinds of pollutants, such as excessive organic matter, pesticides, heavy metals, industrial effluents that are produced and dumped into them by man. This really influences algae and other organisms present in water.

Fresh Water Habitats:

Fresh water habitats include mountain streams, ponds, rivers, lakes, tanks, and brief rainwater puddles. In Nigeria, rice and other flooded areas where standing water is present for many months, are rich in nitrogenfixing cyanobacteria like Rivularia,Aulosira, Cylindrospermum, Gloeotrichia, Nostoc, Anabaena, Aphanothece and few green algae Draparnaldiopsis, Oedogonium, Chaetophora and Coleochaete, and desmids and diatoms.

In slow flowing rivers with rocky shore one may discover several filamentous algae such as spirogyra Oedogonium and Cladophora as wide floating mats usually attached to under water rock boulders. Surface of submerged rocks also illustrates different kinds of attached epiphytic algae such as diatoms, desmids and cyanbacteria. Algal flora also exhibits seasonal variation relying on turbidity and rate of flow of water and other seasonal factors. Algal flora in lake illustrates different communities at different regions. Near shores and at bottom (benthos) thick mats of Oedogonium, spirogyra, nitela, Chara, and a number of epiphytic algae such as Chaetophora, Coleochaete, desmids diatoms colonial cyanobacteria, Cladophora budding as tufts on shells of animals are frequently found. Suspended in upper layers of water, unicellular and colonial algae Volvox, Chlamydomonas, Scenedesmus, Microcystis, pandorina, Euglenadiatoms, Anabaena, Anabaenopsis happens as - phytoplankton. These algae are usually small. Phototactic - moving up and down relying on light conditions - floating in day and sinking at night. Al times, when water is rich in nutrients with optimum temperature and sunshine, one specific algal type (Microcystis, Euglena) multiplies extremely rapidly to dominate other algae, resulting in water blooms (flowering of water). Such blooms can be dangerous to fish and other animals which grow in water as they may use all oxygen in water during night. As seasonal water blooms are more general in temperature countries in Nigeria and other tropical countries, permanent bloods of colonial cyanobacterium Microcystis is most common. It forms thick. Bluish green suspension in several standing tanks and lakes make water unfit for human requirements.

Marine Habitats:

Largest number of algae collectively called as seaweeds is housed in sea. Nigeria has extremely long coast lives and these are extremely rich in marine flora.

Seacoast is sometimes flooded and exposed to sun due to the tides. Area between high tide and low tide is called as intertidal zone. Seaweed which grows in intertidal zone face alternate drying and wetting. They are also tightly disconnected and will be discovered floating in open sea. Benthic algae comprise seaweed which are attached to bottom away from shore in deeper water and are never out of water. Their distribution relies on depth of sea to which sufficient light can penetrate. Beds of seaweed may be discovered in very algae can utilize blue wavelengths of light which can be absorbed by red pigment, phycoerythrin. Intertidal zone also called as littoral zone can be distinguished at times into 3 belts, supralittoral, middle littoral and infralittoral belts, each comprising of relations of different but characteristic algae. Algae discovered in various zones differs according geographical location, nature of substratum and other factors. Open sea away from coast in rich in planktonic algae. Marine phytoplankton is rich in diversity and its composition relies on geographical location and seasons diatoms form main bulk of phytoplankton, Cyanophyta, Dinophyta, silicoflatellates and other groups also happen but in less quantities. At times, sea water turns into colored because of thick pink blooms of Noctiluca and few other algae. Cyanbacterial bloom of Trichodesmium may cover large area of sea providing red color as in Red Sea. Rarely, few dinoflagellates (toxic) numerous very fast and form blooms usually called as red tides. Phytoplanktons of sea play the significant role in main production of organic matter, photosynthetic carbon fixation and serves as food for crustaceans, fingerlings of several fishes and even whales. Every marine living organisms are directly or indirectly dependent on development and activities if phyplankton. In recent year small organisms collectively called as picoplankton comprising Nannochloris, Chlorella nana, Dolichomastix, Micromonas, and Hilba have been discovered to play very significant role in biological productivity of oceans.

Special Habitats:

Algae are also placed in special habitats where environmental circumstances are in extreme.

1) Brines and Salt Lakes:

Inland lakes comprise sodium chloride and other salts in saturating concentrations (brines). One can observe in them wide floating blue-green scums of enduringly growing cyanobacteria Anabaena, Anabaenopsis and unicellular green alga Dunaliella. Metabolism if these halphilic organisms is active only at high salt concentration.

2) Thermal Regions:

Among lower Himalayas and other mountain hot water thermal springs with temperatures ranging from 40^o to 70^o is found that is a house of fairly number of algae, mostly Martigocladus laminosus, synechococcus lividus, cyanobacteria, Oscilatoria and Phormidium. Unlike in other algae, development and metabolism the thermal algae are most active at high temperatures.

3) Polar Regions:

Algae can also develop in very cold climate circumstances which prevail at Arctic and Antarctic regions. Among cyanobacteria-Nostoc is most general, besides Lyngbya, Oscilatoria, Schizothrix, Phormidium and stigonema. Lichens with algal symbionts (collema) are of common occurrence. Cynobacteria and lichens produce and fix nitrogen under of algae generally diatoms and cyanobacteria. On permanent snow fields where surface is stable at least for few weeks' rich growth of algae is located providing red brown or yellow color to snow. Red snow is occurred by green algae Chlamydomonas nivalis and C.flavo-virens.

Soil and Subaerial Algae:

Soil Algae:

Surface layers of solid all over the world give favorable substratum when wet for development of some kinds of algae. Terrestrial algae play the major role as main colonizers on recently exposed areas and help in establishment of other plants in accumulation of humus. After destruction of all life by eruption of volcano on island of Krakatoa in 1883, first organisms which appeared were cyanobacteria such as Tolypothrix, Anabaena, Lyngbya and Symploca.

Soil algae develop abundantly on damp or moist soil, though several of them can endure prolonged and severe dry conditions. several cyanobacteria (Porphyrosilhon, Nostoc Cylindrospermum, scytonema, Tolypothrix, Aphanocapsa, Phormidium, Stigonema, Lyngbya,) green algae (Oedogoium, Oedocladium, Uronema) and other algae (Botrydium, Vaucheria diatoms) grow on surface of soil, that is temporarily moist at least brief time during seasons. They form crust over surface of soil, particularly cyanobacteria that contain mucilaginous sheaths and prevent erosion of top soil.

Subaeria Algae:

Subaerial algae get their water from moisture in air and grow if moisture is available. They are capable of lasting drought like soil algae. All over one can see dark brown patches, at times with velvety carpet like cushions covering extensively exposed surfaces of walls, building, asbestos roofs, terraces, rock surfaces and also tree trunks. Ancient archeological monuments, temples and actually, any lime coated or lime plastered surfaces from excellent habitat for development of cyanobacterial cushions on which seeds of higher plants colonize and eventually bring out ruin and destruction of structure. Algal growth is mostly cyanobacterial in nature comprising of Myxosarchina,Chroococcus, scytonema. Tolypothrix, Porphyrosiphon, Lyngbya, Syechococcus. Every forms illustrate thick layers of mucilaginous sheath deep brown in color. Bark of several tree trunks also harbors not only above algae but also some green like Physolinum, Trentepohlia, (orange tufts) and Chlorococcum

Algal Associations:

Algae live related with other plants and inside animals as explained below.

1) Algal - plant Associations:

Algae are known to be related with other plants, few as epiphytes attached to outer surface and few inside tissues as endophytes are common in all groups of aquatic algae. One exciting case is a green endophytic alga Cephaleuros that grows just below cuticle of leaves of tea (red rust disease of tea) mango, coffee, guava and other fruit bearing trees, as rusty red colored patches. Another endophytic alga Chlorochytrium is discovered in intercellular spaces of water plants Lanna, Ceratophyllum and Elodea. Coleochaete nitellarum happens inside cuticle of another alga Nitella. Many species of brown algae Ectocarpus and sphacelaria develop as endophytes in larger kelps -Laminaria and cystoseira.

2) Algal-Animal Association:

There are nine number of examples where algae are discovered growing inside animals (endozoic). Green alga Chlorella is discovered inside unicellular Paramaecium, in tentacles of Hydra and in sponges. In marine habitats, sea anemones, and few corals have unicellular algae-zooxanthellea (Cryptophyta) and also some Dinophyta members. Platymonas (green alga) found inside marine worm convolute.

3) Algal-Symbiotic Associations:

When the agal lives in close association with the non-photosynthetic organism (fungus or animal), due to its skill to fix carbon photosynthetic some of carbon fixation products like sugars may be absorbed by non-photosynthetic host, while alga in turn may get some kind of protection. This type of equally advantageous association is called as symbiois. Where alga is also nitrogen-fixer as in some cyanobacteria, nitrogenous compounds are also available to host organism along with carbon compounds.

Many cyanobacteria and also some green algae happen in symbiotic association with fungi as distinct group called as lichens. Nitrogen-fixing cyanobacteria are discovered in symbiotic association with photsynatically active plants, bryphytes, pteridophytes gymnosperms and angiosperms.

They are mainly found in intercellular spaces forming coralloid (calcarious) nodules as in Cycas. Azolla, a water fern contains packets of Anabaena in leaf cavities. In case of marine diatom - Rhizosolenia (unicellular), single filament of cyanobacterium Richelia intracellularis, maybe nitrogen-fixer is found. Such intercellular existence has been seen also in unicellular flagellate paulinia and Oocystis, where cyanobacteria-like bodies have been found. Cyanophora (crytophyte) also illustrates such cyanobacteria-like intracellular inclusions. These are called as cyanelles and under electron microscope they seem to have prokaryotic structure but without appropriate cell walls.

A prokaryotic alga Prochloron didemni exists as the cymbiont in gut of sea squirts. This alga and another Prochlorothrix hollandica illustrate prokaryotic structure like cyanobacteria in every respects except that they have chlorophyll b also but no phycobilins). In few phytoflagellates (green alga or cryptomonad) cyanobacterial cells exist in symbiotic association. Host cell is known cyanomes, cyanobacteria cell cyanelles and association is known as syncyanosis.

Intracellular existence of one alga inside another is also discovered in Dinophyta. Unicellular, colorless alga peridinimum balticum and Glenodinum have in their cytoplasm unicellular chrysophytes as endosymbiont. In all above cases it is to be noted that host cell being colorless relies on photosynthetic endosymbiont for organic carbon compounds. The extreme of case of symbiotic state is presence of chloroplasts (not complete cells) in tissues of marine animals. The marine slug-Saccoglossa feeds on marine green algae like Codium. Chloroplasts of alga instead of being digested are included into epithelial cells of digestive tract of animal. Animal seems green in color and chloroplasts actively photosynthesize in light like normal cells. Existence today of such varied symbiotic associations, especially those examples where colorless eukaryotic cell is settled by prokaryotic cyanobacteria-like organism, strongly supports supposition that chloroplasts of higher plants evolved from ancestral cyanobacteria - like endosymbionts.

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