Water as Habitat
Water forms the
habitat of enormous variety of organisms like algae, fishes and whales. These
habitats can be classified into two
It is composed of
habitat: Slow moving, Still/Standing waters such as lakes, reservoirs and
Swiftly moving, running waters such as springs, streams and rivers.
depends upon various physical factors like temperature, depth ,altitude, light
and chemical factors like oxygen, nitrogen, carbon dioxide etc.,
ü Phytoplankton: Volvox, Oedogonium etc.,
ü Floating plants : Pistia, Lemna etc.,
ü Submerged plants: Vallisneria, Zoster
ü Marginal plants: Cattail, Papyrus etc.,
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
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
It is the most important factor which affects the life in aquatic
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.
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.
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.
& 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.
These are the largest habitat when
compared to land and fresh water bodies. The conditions in the oceans are
different from others.
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.
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
ü Aphotic zone: 200 – 600 mts depth,
light is not adequate.
ü Abyssal zone: 200 mts down to the sea
bed, light is absent.
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
ü Pelagic zone: Ocean basin
ü Littoral zone: Sea floor along with
ü Benthic zone: Sea floor along with continental slope
Based on the movement of the organisms
they are of three types
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)
Corals, Shrimps, Crabs etc.,
These are actively swimming organisms
found on the surface of deep water with well developed locomotary organs.
Turtles, Snakes, Whales, Fishes etc.,
These are the bottom dwelling
organisms which crawls over the water.
Crabs, Sea cucumbers etc.,
between Fresh water habitat & marine water habitat
The organisms living in the marine water habitat
have different adaptations from that living fresh water habitat.
All the areas are interlinked with each other whereas
the land and fresh water bodies are not continuos and are separated from each
There is a mixing of water from one ocean to
other whereas not in fresh water.