Estuarine habitat is formed where a big river enters a sea. At this point, salt water from the sea mixes with freshwater from the river to form intermediate water known as brackish water or estuarine.

The salinity (salt content) of estuarine habitat is determined by the distance from the sea, high or low tides and dry or rainy season.


Types of estuaries

  1. Delta — Where a river divides into many channels before entry into ocean or sea.
  2. Lagoon — A body of ocean water that enters into the land through a canal and therefore has the opportunity of mixing of mixing with freshwater from river. It can rejoin.
  3. Bay — A little or small portion of the sea water which enters the into the land and mixes with freshwater from rivers and streams. Lagoon is longer than Bay and can rejoin the sea of another end while bat cannot.


Characteristics of estuarine habitat

  • Salinity fluctuates.
  • It has saturated soil which lacks oxygen.
  • It has mild wave action.
  • It has restricted number of organisms because of its zonations— it has three zones.
    • Zone near the sea which is inhabited by marine organisms.
    • Zone near freshwater which is inhabited by freshwater organisms only.
    • Zone in-between which is the true estuary and which is inhabited by estuarine organisms.
  • Water is affected by tides; sea water usually flows rapidly into estuaries at high tide and rushes back into the ocean at low tides.


Living organisms found in estuary

Plants e.g.

Phytoplanktons e.g. diatoms;

Filamentous algae e.g. Spirogyra.

Water lettuce and bacteria.

Other plants are red mangrove and white mangrove.

Animals are mudskipper (fish), barnacles and hermit crab.


Adaptation of estuarine organisms

Organisms Adaptations
Rhizophora racemosa (red mangrove) Seeds germinate on parent plants and seedling fall off parent plant.

Seedling has large cotyledon which for the seedling.

Seedling has rootlets for anchorage and for absorption into the soft mud.

Seedling grows very fast and produce prop roots.

Plants has thick leathery leaves to reduce loss of water through transpiration.

Avicenia nitida (white mangrove) Possession of breathing roots called pneumatophore which has spongy tissues for absorbing atmospheric air.

Ability to excret excess salt through the leave to reduce excess salt in the body.

Leaves have excess cuticle to reduce transpiration.

Mudskipper Has several methods of locomotion eg swimming, hopping, wringling or flapping to escape danger.

Has gills for respiration and lungs for respiration on land.

Hermit crabs Lives in empty shells of snails for protection.


Food Chain in Estuarine Habitat.

A typical food chain in an estuarine habitat may have up to three, four or five trophic levels. The phytoplanktons such as diatoms and detritus form the basic producers which support the food chain. Some examples of food chains in the estuarine habitat are:

  1. Detritus —> worms —> snails —> birds
  2. Diatoms —> Shrimps —> fishes
  3. Phytoplanktons —> barnacles —> fish —> birds
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