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1. Neuston
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These organisms are free-floating and live at the interface between air and water. They are not anchored to any surface and include species like floating aquatic plants and similar life forms.
- 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. Example: beetles and back-swimmers.
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2. Periphyton
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- 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 of animals.
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3. Plankton
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- 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.
- The locomotory power of the planktons is limited so that their distribution is controlled, largely, by currents in the aquatic ecosystems.
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4. Nekton
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- This group contains animals which are swimmers.
- The nektons are relatively large and powerful as they have to overcome the water Currents.
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5. Benthos
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- The benthic organisms are those found living in the bottom of the water mass.
- Practically every aquatic ecosystem contains well developed benthos.
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