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Water as Habitat & Adaptations
2013-03-03, 8:00 PM

Water as Habitat & Adaptations

Water forms the habitat of enormous variety of organisms like algae, fishes and whales. These habitats can be classified into two types namely

ü  Fresh water habitat

ü  Marine water habitat


Ø  Fresh water habitat

It is composed of

ü  Lentic habitat: Slow moving, Still/Standing waters such as lakes, reservoirs and ponds.

ü  Lotic habitat: Swiftly moving, running waters such as springs, streams and rivers.

·         Flora & Fauna

It depends upon various physical factors like temperature, depth ,altitude, light and chemical factors like oxygen, nitrogen, carbon dioxide etc.,

§  Flora

ü  Phytoplankton: Volvox, Oedogonium etc.,

ü  Floating plants : Pistia, Lemna etc.,

ü  Submerged plants: Vallisneria, Zoster etc.,

ü  Marginal plants: Cattail, Papyrus etc.,

§  Fauna

ü  Coelenterates : Hydra

ü  Platyhelminthes: Turbellerians

ü  Annelids: Leeches,

ü  Arthropods: Crustaceans

ü  Mollusks: Gastropods

ü  Pisces: Fishes

ü  Reptiles : Tortoise

ü  Amphibians: Frogs

ü  Aves : Birds


Ø  Characters/Factors

·         Salt content

It is very low in fresh water (1.8%) most of it is derived from the death and decomposition of animal bodies and from the rains.

In small ponds and lakes, salt content increases during summer due to the evaporation of water where as in monsoon it decreases due to the inflow of large amount of rain water.

·         Temperature

It is the most important factor which affects the life in aquatic habitat.

In small ponds and lakes the entire water gets heated up during day time and cools down during night time because they are not very deep whereas as in deeper lakes only surface water is heated up while the deeper layers remain cool. This affects the organisms living in various depths.

Example: Small organisms of ponds and lakes move to the deeper layers of water during daytime and come to the surface layers during night time.

·         Sunlight

The distribution of light plays a key role in development and distribution of water to flora and fauna.

Light can penetrate easily in the deeper water but it is very difficult to penetrate in the turbid water.

·         Osmotic pressure

When compared to the salt content in the cells of living organism the content of fresh water is hypotonic because of these two different concentration gradients. The fresh water flows in to the organism if total volume is allowed cell wall burst and will dies. For that animal have contractile vacuole, flame cells and dissolved nutrients to remove the excess water.

·         Oxygen & Dissolved nutrients

The organisms which are living in the water takes the oxygen which is dissolved in the water.

Oxygen dissolved in water comes from different sources i.e. air, aquatic plants. The deeper layers of water get oxygen by diffusion from surface layers. As the depth increases amount of oxygen dissolved in water decreases hence animals living in greater depths should be able to tolerate less amount of oxygen.

Solubility of oxygen is more at low temperature decreases with increase in concentration. In summer both temperature and salt content increases hence reduces the oxygen content of water.

Ø  Marine Water

These are the largest habitat when compared to land and fresh water bodies. The conditions in the oceans are different from others.


Ø  Characters/Factors

·         Salt content

It is very high (3.5%) and almost constant at different oceans because of circulation and mixing up of sea water by tides and currents. The common salt is Nacl and other elements are in dissolved state (chlorides, carbonates, sulphates, potassium, magnesium and calcium).

The organisms which are living in the sea water requires special protection against the high salt content of water to prevent the water loss from the body.


·         Light

The living conditions in seas waters depend upon the light penetration. Based in this they are of three types


ü  Euphotic zone: 200mts depth, light is adequate.

ü  Aphotic zone: 200 – 600 mts depth, light is not adequate.

ü  Abyssal zone: 200 mts down to the sea bed, light is absent.


·         Temperature

It decreases with increase in depth. In oceans, surface water gets heated up by sunlight and temperature is very high (30⁰c).Less amount of heat is received by deeper water of oceans.

The temperature in abyssal zone is 2⁰c, temperature of surface water may shoe seasonal fluctuations while in deeper layers it is constant through the year.


Ø  Types of Zones

ü  Pelagic zone: Ocean basin

ü  Littoral zone: Sea floor along with continental shelf.

ü  Benthic zone:  Sea floor along with continental slope


Based on the movement of the organisms they are of three types 

·         Plankton

These are the small organisms which floats and drifts passively on the surface of water by the waves, currents and winds.Locomotary organs are absent. They includes phytoplankton (diatoms) and zooplankton (protozoan’s)

Examples: Corals, Shrimps, Crabs etc.,

·         Nekton

These are actively swimming organisms found on the surface of deep water with well developed locomotary organs.

Examples: Turtles, Snakes, Whales, Fishes etc.,

·         Benthos

These are the bottom dwelling organisms which crawls over the water.

Examples: Crabs, Sea cucumbers etc.,


Ø  Differences between Fresh water habitat & marine water habitat

ü  The organisms living in the marine water habitat have different adaptations from that living fresh water habitat.

ü  All the areas are interlinked with each other whereas the land and fresh water bodies are not continuos and are separated from each other.

ü  There is a mixing of water from one ocean to other whereas not in fresh water.


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