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ALGAL ECOLOGY
INTRODUCTION:
Algal ecology refers to the relationship or interaction of algae with other organisms and with the physical and chemical environment. To say that the algae are of universal occurrence will not be an exaggerated statement because of their presence in nearly all types of habitats.
DISTRIBUTION OF ALGAE IN DIVERSE HABITAT:
Algae are found in fresh as well as sea water, on soil, on and within other plants and even animals, on rocks, stones and in desert as well as on permanent snowfields, etc. They are distributed or taken away from their place of occurrence to other parts through some vectors, such as tides, water currents, wind movements, animal movements, ships or aquatic birds, etc. (Atkinson, 1972; Schlichting, 1974). On the basis of their habitat, algae can be categorized as follows:
- AQUATIC ALGAE:
The aquatic environment comprises about 70 per cent of the surface of the earth, and here the algae are of great importance as primary producers of elaborated organic materials. In this way, algae play a critical role in the economy of both freshwaters and seas and oceans. They may be freshwater algae or marine algae.
a) Freshwater Algae:
Enormous number of algae occur in waters of low salinity, called freshwater. They grow even in as low a salinity as 10 ppm in water surroundings like ponds, tanks, ditches, lakes, puddles, etc.
Common freshwater algae are Zygnema, Spirogyra, Oedogonium, Cladophora, Chara, Nostoc, Oscillatoria, Rivularia , etc.
Many algae grow in brackish water (Oscillatoria ,Anabaena , etc.). Such waters are unpalatable for drinking, and contain less salt than sea water but more than freshwater.
Most common macroscopic alga reported from freshwater springs isBatrachospermum and several diatoms, e.g.Achnanthes lanceolatus, Denticula tenuis, Fragilaria pinnata andMeridion circulare.
Common planktons reported from streams of colder regions includePediastrum boryanum, Melosira varians, Synedra ulina, Nitzschia sigmoidea andFragilaria virescens.
Algae found commonly in the flowing waters of the rivers of colder regions includeBacillaria paradoxa, Cyclotella atomus, C. striata, Nitzschia acicularis andStephanodiscus astreae.
Small ponds or puddles of colder regions contain desmids (e.g.Cosmarium ,Euastrum ), diatoms (e.g .Pinnularia, Frustulia, Eunotia ) along with species of Volvocales, Chlorococcales, flagellates and blue-green algae (e.g.Synura, Uroglena, Peridinium, Chroococcus ).
b) Marine Algae:
Algae of the sea water are called marine algae. They grow generally in waters where the solutes are usually 30–44 parts per thousand (%0). Marine vegetation occupies only about 2% of the general surface (shorelines and zone of relatively shallow water) of the sea, of which a large part is occupied by the phytoplankton, mainly of the diatoms and dinoflagellates. Some of the common marine algae areSargassum, Laminaria, Bangia, Rhodymenia, Padina, Caulerpa, Polysiphonia , etc.
Planktonic Algae:
Many freshwater and marine organisms which can float easily in water from one place to other are called planktons. The term 'planktonic algae' refers to those forms of algae found floating or freely swimming in water. Among the freshwater planktonic algae, forms such asChlorella ,Scenedesmus ,Hydrodictyon , Chlamydomonas ,Volvox andEudorina of Chlorophyceae,Euglena andPhacus of Eugleninae;Microcystis , Anabaena ,Aphanotheca ,Spirulina ,Arthrospira ,Anabaenopsis andOscillatoria of Myxophyceae and Melosira, Cyclotella ,Pinnularia ,Navicula ,Fragilaria andAsterionella of Bacillariophyceae are common while among marine planktonic formsPhalacroma ,Dinophysis ,Exuviaella andProrocentrum of Desmophyceae.
Benthic Algae:
The term ‘benthic algae’ refers to aquatic algae found attached to one or the other substratum. Among the freshwater forms,Cladophora ,Pithophora ,Chara ,Nitella etc., and among marine forms most members of Phaeophyceae and Rhodophyceae are the common examples. Cladophora , Enteromorpha , Porphyra , Polysiphonia ,Sargassum ,Laminaria ,Chondrus ,Ulva ,Ectocarpus ,Sphacelaria , &Acetabularia.
2. TERRESTRIAL ALGAE:
Algae, found on the soil in the form of a green scum, are called terrestrial algae. The soil flora is collectively known as edaphophytes (Prescott, 1969). It is further divisible into surface soil flora known as sapophytes or epiterranean, and under-soil flora called cryptophytes or subterranean. Some of the algae in the soil even occur up to the depth of 1 m or even more. Some of the common terrestrial algae areFritschiella, Chlorella, Vaucheria, Euglena, Chlamydo monas, Lyngbya, Navicula, Caloneis, Pinnularia, Hormidium, Anabaena, Chroococcus, Oscillatoria andPhormidium.
Friedmann et al. (1967) and Friedmann and Ocampo (1976) observed many small-sized algae from desert soils. Their water supply is maintained mainly from dew. The desert soil algae have been classifi ed into the following 5 categories by Friedmann and his co-workers:
- Endedaphic : Algae living in the desert soil.
- Epidaphic : Algae living on the desert soil surface.
- Hypolithic : Algae living on the lower surface of stones on desert soil.
- Chasmolithic : Algae living in the rock fi ssures in desert soil.
- Endolithic : Rock penetrating desert algae.
3. ALGAE OF UNUSUAL HABITAT:
Besides Aquatic and Terrestrial, Algae are found in different habitats and they are named according to their habitats:
a) Lithophytic algae:
These are found on the moist surfaces of rocks and stones, e.g.Batrachospermum andEnteromorpha. In the freshwater surroundings, the rocks receiving only atmospheric moisture possess the algal genera such asTrentepohlia ,Desmococcus ,Mesotaenium , andCylindrospermum. Rocks and stones of marine surroundings contain a rich algal flora, of which some common ones are several species of Pelvetia, Fucus, Porphyra, Bangia, Sargassum, Laminaria andAscophyllum.
Tokida (1960) reported 106 species of epiphytic algae on a single genus,Laminaria. He reported 285 algal species on Laminariales growing epiphytically. OnLaminaria hyperborea four major epiphytic algae areRhodymenia pseudopalmata, Phycodrys rubens, Membranoptera alata andPtilota pulmosa.
Bryophytes and angioperms of rivers are generally coated with epiphytic algae. They are mainly the representatives of diatoms (Achnanthes, Tabellaria, etc.), desmids (Cosmarium ) or blue-green algae (Nostoc, Oscillatoria and Tolypothrix ).
h) Endophytic algae:
Algae occurring within or among the other cells of other plants are called Endophytic algae.Nostoc in the thallus of Anthoceros,Anabaena cycadearum in the coralloid roots of Cycas, andAnabaena azollae in Azolla show an association of mutual benefit. Such type of algae also known as Symbiotic algae. because they live in association with dissimilar organisms for their mutual benefit. However, lichens are the best examples of symbiosis where the association lies in between algae and fungi.
i) Epizoic and Endozoic algae:
Algae occurring on and within animals are known as epizoic and endozoic, respectively.Cladopora crispata grows epizoically on the shells of molluscs, whereasStigeoclonium in the nose of fishes, Chlorella in Hydra and sponges occur endozoically.
j) Parasitic algae:
Some of the algae also occur parasitically on plants and animals. A few of them are listed below:
1.Cephaleuros (of Chlorophyceae) on the leaves ofMagnolia andThea sinesis 2.Phyllosiphon (of Chlorophyceae) on the leaves ofArisarum vulgare. 3.Rhodochytrium (of Chlorophyceae) on ragweed leaves. 4.Polysiphonia fastigiata (of Rhodophyceae) occurs semiparasitically onAscophyllum nodosum. 5.Ceratocolax (of Rhodophyceae) in the thalliPhyllophora. 6.Callocolax (of Rhodophyceae) onCallophyllis.
CONCLUSION:
To sum up, Algae are presence in nearly all types of habitats and they are named based on their distribution in different habitats. The distribution of algae from their place of occurrence to other parts are responsible by different vectors as already mentioned in the beginning.
