⦿ The aquatic organisms are classified on the basis of their zone of occurrence and their ability to cross these zones.
⦿ The organisms (both flora and fauna) in the aquatic ecosystem are unevenly distributed but can be classified on the basis of their life form or location into five groups.
Neuston
Periphyton
Plankton
Nekton
Benthos
Neuston
⦿ These are unattached organisms which live at the airwater interface such as floating plants, etc.
⦿ 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.
Periphyton:
⦿ These are organisms which remain attached to stems and leaves of rooted plants.
⦿ Substances emerging above the bottom mud such as sessile algae and their associated group of animals.
Plankton
⦿ This group includes both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans (zooplankton) found in all aquatic ecosystems, except certain swift moving waters
⦿ Their distribution is controlled, largely, by currents in the aquatic ecosystems.
Nekton
⦿ This group contains animals which are swimmers
⦿ The nektons are relatively large and powerful as they have to overcome the water currents
⦿ The animals range in size from the swimming insects (about 2 mm long) to the largest animals, the blue whale.
Benthos
⦿ The benthic organisms are those found living in the bottom of the water mass
⦿ The benthic organisms are those found living in the bottom of the water mass.
