Aquatic Ecosystems | Environment for UPSC 2025 (Pre & Mains) PDF Download

 Page 1


AQUATIC 
 ECOSYSTEMS 
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AQUATIC 
 ECOSYSTEMS 
COMPONENTS 
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AQUATIC 
 ECOSYSTEMS 
COMPONENTS 
Aquatic ecosystems are classified on the basis of salinity into 
following types 
Fresh water ecosystems — Water on land which is 
continuously cycling and has low salt content (always less 
than 5 ppt) is known as fresh water.  
There are two types of fresh water ecosystems:  
Static or still water (Lentic) ecosystems e.g. pond, lakes, etc 
Running water (Lotic) ecosystems e.g. streams and rivers. 
 
Marine ecosystems — 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. 
 
Brackish water ecosystems — these water bodies have salt 
content in between 5 to 35 ppt.  
E.g. estuaries, salt marshes, mangrove swamps. 
 
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AQUATIC 
 ECOSYSTEMS 
COMPONENTS 
Aquatic ecosystems are classified on the basis of salinity into 
following types 
Fresh water ecosystems — Water on land which is 
continuously cycling and has low salt content (always less 
than 5 ppt) is known as fresh water.  
There are two types of fresh water ecosystems:  
Static or still water (Lentic) ecosystems e.g. pond, lakes, etc 
Running water (Lotic) ecosystems e.g. streams and rivers. 
 
Marine ecosystems — 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. 
 
Brackish water ecosystems — these water bodies have salt 
content in between 5 to 35 ppt.  
E.g. estuaries, salt marshes, mangrove swamps. 
 
 
AQUATIC ORGANISMS 
 
They are classified on the basis of their zone of occurrence. 
Neuston These organisms live at the air-water interface e.g. floating 
plants. 
Periphyton These are organisms which remain attached to stems and 
leaves of rooted plants or substances emerging above the bottom 
mud such as sessile algae. 
Plankton Microscopic floating organisms such as algae, diatoms, 
protozoans and larval forms are called plankton.  
This group includes both microscopic plants like algae 
(phytoplankton) and animals like crustaceans and protozoans 
(zooplankton). 
The locomotory power of the planktons is limited so that their 
distribution is controlled, largely, by currents in the aquatic 
ecosystems. 
Nekton This group contains powerful swimmers that can overcome 
the water currents. 
Benthos The benthic organisms are those found living in 
the bottom of the water mass. 
 
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AQUATIC 
 ECOSYSTEMS 
COMPONENTS 
Aquatic ecosystems are classified on the basis of salinity into 
following types 
Fresh water ecosystems — Water on land which is 
continuously cycling and has low salt content (always less 
than 5 ppt) is known as fresh water.  
There are two types of fresh water ecosystems:  
Static or still water (Lentic) ecosystems e.g. pond, lakes, etc 
Running water (Lotic) ecosystems e.g. streams and rivers. 
 
Marine ecosystems — 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. 
 
Brackish water ecosystems — these water bodies have salt 
content in between 5 to 35 ppt.  
E.g. estuaries, salt marshes, mangrove swamps. 
 
 
AQUATIC ORGANISMS 
 
They are classified on the basis of their zone of occurrence. 
Neuston These organisms live at the air-water interface e.g. floating 
plants. 
Periphyton These are organisms which remain attached to stems and 
leaves of rooted plants or substances emerging above the bottom 
mud such as sessile algae. 
Plankton Microscopic floating organisms such as algae, diatoms, 
protozoans and larval forms are called plankton.  
This group includes both microscopic plants like algae 
(phytoplankton) and animals like crustaceans and protozoans 
(zooplankton). 
The locomotory power of the planktons is limited so that their 
distribution is controlled, largely, by currents in the aquatic 
ecosystems. 
Nekton This group contains powerful swimmers that can overcome 
the water currents. 
Benthos The benthic organisms are those found living in 
the bottom of the water mass.