These are unattached organisms which live at the air-water interface such as floating
Some organisms spend most of their lives on top of the air-water interface such as
water striders, while others spend most of their time just beneath the air -water interface
and obtain most of their food within the water.
E.g., beetles and back-swimmers.
These are organisms which remain attached to stems and leaves of rooted plants or
substances emerging above the bottom mud such as sessile algae and their associated group
This group includes both microscopic plants like algae (phytoplankton) and
animals like crustaceans and protozoans (zooplankton) found in all aquatic
ecosysteins, except certain swift moving waters
The locomotory power of the planktons is limited so that their distribution is
controlled, largely, by currents in the aquatic ecosystems
This group contains animals which are swimmers.
The nektons are relatively large and powerful as they have to overcome the water
The benthic organisms are those found living in the bottom of the water mass.
Practically every aquatic ecosystem contains well developed benthos
Sunlight penetration rapidly diminishes as it passes down the column of water.
The depth to which light penetrates a lake determines the extent of plant distribution.
Based on light penetration and plant distribution they are classified as photic and
It is the upper layer of the aquatic ecosystems, up to which light penetrates and within
which photosynthetic activity is confined.
The depth of this zone depends on the transparency of water.
photic (or ."euphotic") zone is the lighted and usually well-mixed portion that extends
from the lake surface down to where the light level is 1% of that at the surface.
The lower layers of the aquatic ecosystems, where light penetration and plant growth
are restricted forms the aphotic zone.
Only respiration activity takes place.(photic-both respiration and photosynthesis take place )
Aphotic zone is positioned below the littoral and photic zones to bottom of the lake where
light levels are too low for photosynthesis.
This deep, unlit region is also known as the profundal zone
Oxygen enters the aquatic ecosystem through the air water interface and by the
photosynthetic. average concentration of dissolved oxygen as 10 parts per million by weight.
Dissolved oxygen escapes the water body through air -water interface and through
respiration of organisms (fish, decomposers, zooplanktons, etc )
The amount of dissolved oxygen retained in water is also influenced by temperature.
The water temperature changes less rapidly than the temperature of air because
water has a considerably higher specific heat than air.
Since water temperatures are less subject to change, the aquatic organisms have
narrow temperature tolerance limit
The salt content of fresh bodies is very low, always less than 5 ppt
(parts per thousand). E.g lakes, ponds, pools, springs, streams, and rivers
the water bodies containing salt concentration equal to or above that
of sea water (i.e., 35 ppt or above). E.g shallow seas and open ocean
these water bodies have salt content in between 5 to 35 ppt. e.g.
estuaries, salt marshes, mangrove swamps and forests