Biodiversity is an unique feature of our biosphere,sustainability of which is directly related with the existence of human civilization. As we do recognize ‘biodiversity’ in the terrestrial and marine ecosystems we also do recognize the same in inland aquatic ecosystems, a domain of the subject of Limnology.
Limnology is a discipline which deals with the functional relationship among organisms of inland aquatic ecosystems and their productivity which in turn is affected by the dynamism of the physical, chemical and biological actors operating therein (Wetzel 1983).
Biodiversity includes both plants and animalcules. ‘Plant Diversity’ is one of the components of the ‘Aquatic Biodiversity’ and is a focal point of the primary production of any water body.
In aquatic environment where water is the surrounding medium, the diversities of plants may range from a photoautotrophic bacteria and/or a tiny algal cell to a huge aquatic tree Barringtonia acutangula. We come to this enormous issue later on. But before which we must identify the reasons why and how plants got into water and able to live there?
Scientists believe that the physical properties of water is the sole reason to convert aquatic habitat as an excellent medium to support life. These are:
1. Density of water: Which is 760 times greater than air, so water creates a buoyant effect upon the body of an organism to the same magnitude. Organisms would feel easy to move in water.
2. Viscosity of water which is 750 times more than air, likewise the dragging effect on the body of organisms is also greater.
3. High latent heat of water which helps to keep a stable temperature condition in water compared to a same volume of air.
4. Low diffusivity of molecules in water, as a result water movement in the form of wave and current are necessary for the uniform distribution of nutrients.
5. High turbidity and a steep gradient of light from top to the bottom of a water column help to create new microclimatic environment within a very small space.
Creation of biotic community in the aquatic ecosystem
Because of above mentioned physical features of water some distinct limnological zones are created in a single water body, based on which organisms start growing.
Photoautotrophic organisms start colonizing in the upper limnetic area, on the other hand heterotrophic and chemolithotrophic organisms colonize lower darkened area.
In the epilimnion a replacement of ‘old production’ by newly produced organic matter is also necessary. This is done by an one way flow of sedimentation from top to the bottom of the lake.
Via sedimentation old primary productivity reaches to the bottom of the lake where bacterial decomposition goes on to release new nutrients.
To bring this nutrients in the upper lighted area circulation is necessary.
In dimictic lakes these are common features occurring simultaneously in autumn and spring seasons of the year.
From the above discussion it is clear that the aquatic biodiversity is a function of a number of microclimatic zones which are formed throughout the horizontal layer and vertical columns of water. So, a precise classification of aquatic biodiversity is possible depending on their habitat and niche. Following is a summary of it:
1. Autotrophic: who can produce their own food i.e. all chlorophyll bearing plants (Scenedesmus arcuatus, Cryptomonas ovata) and chemosynthetic bacteria (Chromatium okenii, Thiospirillum jenense)
2. Photoautotrophic: who utilize solar energy, chlorophyll and water for the synthesis of their food as carbohydrate i.e., all green plants e.g., a macrophyte Potamogeton crispus.
3. Chemolithotrophic: These are bacteria which absorb energy by taking electron from inorganic substances e.g., Nitrosomonas, Nitrobacter.
4. Chemoorganotrophic: who absorbs energy by taking electron from organic sbubtances e.g., Cytophaga, Pseudomonas aeruginosa.
5. Heterotrophs: those are unable to synthesize their own food rather depend on others for food, e.g. a predatory fish Esox lucius.
B. Trophic state
1. Primary producer: Organisms who utilizes sunlight to synthesize carbohydrate. They occupy the 1st trophic level of the food chain based upon which all other organisms live e.g. phytoplankton Chalmydomonas, Mougeotia, etc., macrophyte Ceratophyllum, Najas, etc.
2. Consumer: These are such animalcules who ingest live, dead or half dead organisms e.g., some zooplankton, small fishes, large fishes, reptiles etc.
3. Decomposers: work on all sorts of dead bodies of aquatic organisms, carry out decomposition and brake down complex organic molecules into simpler ones e.g. aquatic virus, bacteria, fungus, etc.
4. Top consumers: Consume secondary production. e.g. fish eating birds, beaver,
snakes, tortoise, crocodiles etc.
1. Pelagic: organisms living in the upper free water e.g. fish, floating macrophyte, filamentous algae etc.
2. Plankton: microscopic drifting organims e.g. Volvox, Daphnia, Cyclops, etc.
3. Phytoplankton: chlorophyll bearing microscopic algae, e.g. Euglena, Trachelomonas, Cryptomonas etc.
4. Zooplankton: microscopic/ macroscopic animal plankton e.g. Bosmina, Leptodora etc.
5. Nekton: organisms able to navigate of its own e.g. fish, water fowl etc.
6. Neuston: microscopic organismns which remain attach to or clinging on the surface of water projecting their body upright in the air or down into water e.g. Codonosiga, Botnyococcus etc.
7. Benthic: all organisms of a water body except those living in the pelagic region e.g Chironomus.
8. Littoral: starts from the margin and extends through the slope of a lake until a point where the last individual of plant is noticed. Lake litoral is mostly occupied by aquatic macrophytes and different kinds of benthic animals e.g. Nymphaea nouchali, Vallisneria, Pila globosa etc.
9. Aquatic macrophytes: macroscopic aquatic plants which can be identified up to genus level with the help of naked eye, main occupants of littoral area e.g. Chara, Nitella, Sagittaria, Najas etc.
10. Epiphytic algae: micro-algae growing on the surface of submerged plant parts, e.g. Characium, Gomphonema etc.
11. Epizooic algae: algae growing on the surface of shells of mollusks, tortoise etc. e.g. Basicla dia, Cladophora, Oedogonium, etc.
12. Epipelic: micro-algae growing as colored layers or burrowing within the submerged soil surface e.g. Navicula, Nitzschia, Euglena etc.
13. Epipsammic: micro-algae growing on the geometrical surface of sand grains e.g. Cymbellonitzschia, Gomphonema etc.
14. Periphyton: organims growing as colored layer or ramain attached or clinging to the surface of any submerged object e.g. Ulothrix, Oedogonium, Gomphonema, Navicula, Nitzschia, Stigeoclonium etc.
15. Other animals: organisms living inside the tissue of aquatic plants or build cases by accunmulating plant debris and live therein e.g. larval stages of many insects, some rotifers, snails etc.
16. Profundal: like to live in the deeper and darkened water of lake bottom. These are mainly decomposers and consumers.
17. Free living organisms: those predatory fishes which stay in the darkened area of the water body to catch the prey easily.
18. Organisms inhabiting mud surface: microzone which is created because of seepage from the sediment, some bacteria, actinomycetes and zooplankton live in this zone.
19. Organisms living inside the mud: mostly soft bodied invertebrates e.g., nematodes, earthworms, oligochaete, snails, mussels etc.
D. Natural classification
This classification has become easier because of the most generalised division of all organisms into two main groups like Plantae and Animalia.
Therefore, organisms belonging to the above mentioned two groups living in water are the main basis of this classification. With this is attached virus.
|Virus for Hepatites, Cyanophage, etc.||Bacteria: Sphaerotilus natens, Chromatium||Protozoa: Diffugia, Paramecium|
|Actinomycetes: Actinoplanes, Streotomyces||Rotifer: Philodine, Brachionus|
|Fungus: Rhizophidium, Allomyces||Crustacea: Leptodora, Cyclops|
|Algae: Scendesmus, Chara||Insects: Tubifex tubifex, Ephemerella|
|Lichen: Verrucaria latebrosa, Umbellicaria pustulata||Mollusks, mussels: Limnaea, Lamellidens|
|Liverworts and Mosses: Riccia fluitans, Fontinalis aquatica||
Bottom living invertibrates:
|Ferns: Salvinia cucullata, Marsilea quadrifolia||Fish: Cyprinus carpio, Wallago altu|
|Angiosperm: Myriophyllum tuberculatum, Pistia stratiotes||Amphibians: Rana tigerina, Paratelphiesa|
|Reptiles: Xenochropis piscator, Gavialis gangeticus|
|Birds: Ardea cinera, Anser anser|
|Mammal: Platanista gangetica|
Thus, Biodiversity in inland aquatic system is an important focal point of limnology. This system plays great role in ecology.
- Farzana Runa on 30 july,2020.
- Tarek Siddiki Taki on 06 Aug, 2020.