Planktons
Victor Hensen introduced the term plankton in 1887 to describe all organisms that drift in the sea. The
name is derived from the Greek word πλαγκτός (planktós), meaning "drifter" or "wanderer," which itself
comes from the verb πλάζω (plázō), meaning "to wander" or "to drift". Initially, Hensen used the
term “halyplankton”, which combined the Greek word for "sea" (ἅλς, háls) with planktós, but later
shortened it to plankton for simplicity.
Definition: Planktons can be defined as the organisms of relatively small size, mostly microscopic
which are unable to move or swim against water currents or air.
These organisms either have relatively small locomotion powers or none at all. They drift in the water,
subject to the action of currents, waves, and other forms of water movement.
Classification/Types
A. Classification of Plankton Based on Nutrition
Plankton can be classified based on their nutritional modes into several categories:
1. Phytoplankton: Plant plankton that produce their own food and act as a producer in any aquatic
ecosystem.
Examples: Cyanobacteria, diatoms, Chlorella, Hydrilla and dino-flagellates are common types of
phytoplankton.
2. Zooplankton: These are heterotrophic organisms that feed on other plankton, including
phytoplankton and smaller zooplankton. They act as primary consumers in the aquatic food web.
Examples: Small protozoans, copepods, krill, and the larvae of fish and other marine animals fall into
this category.
3. Seproplankton: Seproplankton is a term that refers to a specific category of planktonic organisms
that are characterized by their saprotrophic mode of nutrition, i.e., obtain their nutrients by breaking
down dead organic material, such as decaying plant and animal matter. These organisms play a crucial
role in aquatic ecosystems by decomposing organic matter and recycling nutrients.
Examples: Decomposers, typically include various bacteria and fungi that thrive in the water column
and contribute to the decomposition process.
4. Mycoplankton: This group includes fungi and fungus-like organisms that play a role in nutrient
cycling by decomposing organic matter. Mycoplankton contributes to the remineralization of
nutrients in aquatic environments.
5. Bacterioplankton: Comprising bacteria and archaea, these organisms are essential for nutrient
recycling and play a significant role in the decomposition of organic materials. They help
remineralize nutrients that are vital for the growth of phytoplankton.
, 6. Virioplankton: This category includes viruses that infect planktonic organisms. Virioplankton can
influence microbial community dynamics and nutrient cycling in aquatic ecosystems.
7. Mixotrophs: These organisms can switch between autotrophic (photosynthetic) and heterotrophic
(feeding on other organisms) modes depending on environmental conditions.
Examples: Some dinoflagellates exhibit mixotrophic behavior, allowing them to adapt to varying
nutrient availability.
B. Based on the size, planktons are the following type:
1. Macro-planktons: The larger group of planktons that are visible to the naked eye. They occupy
more than 2 mm in size. Examples: Ctenophores, salps, Mysis larva, nymph and amphipods.
2. Meso-plankton: The plankton of middle depths below the penetration of photosynthetically
effective light. Planktons bearing a group length of 200 𝝁m to 2 mm are included in this type.
Examples: Ostracoda, Chaetognaths, Pteropoda, and Tunicata.
3. Micro-plankton: Their size varies from 20 to 200 𝝁m, e.g. Copepods, most of the phytoplankton,
protozoans and large protists.
4. Nano-plankton: Size ranges from 2 to 20 𝝁m, e.g. Protists, Diatoms and Algae.
5. Ultranano-plankton: Very minute planktons with 0.5 to 2 𝝁m in size. Examples: Juvenile
stages of some protozoans.
C. Based on Ecology:
1. Limnoplankton: Limnoplankton refers to planktonic organisms living in lakes. Examples:
Daphnia (water fleas), Rotifers, Fragilaria and various species of freshwater algae.
2. Rheoplankton: Rheoplankton are planktonic organisms that inhabit flowing waters, such as rivers
and streams. They are adapted to survive in environments with significant water movement.
Examples: Examples include certain types of diatoms, phytoplankton like Melosira and small
crustaceans that can withstand currents, like some species of copepods.
3. Heleoplankton: Heleoplankton (uncountable) are planktons that live in still freshwater such as
ponds and marshes. E.g., Euglena.
4. Helio-plankton: Plankton living in marine water. E.g., Chaetoceros.
5. Hypalmyroplankton: Planktons living in brackish water are called hypalmyroplanktons. E.g.,
Chaetophora.
Victor Hensen introduced the term plankton in 1887 to describe all organisms that drift in the sea. The
name is derived from the Greek word πλαγκτός (planktós), meaning "drifter" or "wanderer," which itself
comes from the verb πλάζω (plázō), meaning "to wander" or "to drift". Initially, Hensen used the
term “halyplankton”, which combined the Greek word for "sea" (ἅλς, háls) with planktós, but later
shortened it to plankton for simplicity.
Definition: Planktons can be defined as the organisms of relatively small size, mostly microscopic
which are unable to move or swim against water currents or air.
These organisms either have relatively small locomotion powers or none at all. They drift in the water,
subject to the action of currents, waves, and other forms of water movement.
Classification/Types
A. Classification of Plankton Based on Nutrition
Plankton can be classified based on their nutritional modes into several categories:
1. Phytoplankton: Plant plankton that produce their own food and act as a producer in any aquatic
ecosystem.
Examples: Cyanobacteria, diatoms, Chlorella, Hydrilla and dino-flagellates are common types of
phytoplankton.
2. Zooplankton: These are heterotrophic organisms that feed on other plankton, including
phytoplankton and smaller zooplankton. They act as primary consumers in the aquatic food web.
Examples: Small protozoans, copepods, krill, and the larvae of fish and other marine animals fall into
this category.
3. Seproplankton: Seproplankton is a term that refers to a specific category of planktonic organisms
that are characterized by their saprotrophic mode of nutrition, i.e., obtain their nutrients by breaking
down dead organic material, such as decaying plant and animal matter. These organisms play a crucial
role in aquatic ecosystems by decomposing organic matter and recycling nutrients.
Examples: Decomposers, typically include various bacteria and fungi that thrive in the water column
and contribute to the decomposition process.
4. Mycoplankton: This group includes fungi and fungus-like organisms that play a role in nutrient
cycling by decomposing organic matter. Mycoplankton contributes to the remineralization of
nutrients in aquatic environments.
5. Bacterioplankton: Comprising bacteria and archaea, these organisms are essential for nutrient
recycling and play a significant role in the decomposition of organic materials. They help
remineralize nutrients that are vital for the growth of phytoplankton.
, 6. Virioplankton: This category includes viruses that infect planktonic organisms. Virioplankton can
influence microbial community dynamics and nutrient cycling in aquatic ecosystems.
7. Mixotrophs: These organisms can switch between autotrophic (photosynthetic) and heterotrophic
(feeding on other organisms) modes depending on environmental conditions.
Examples: Some dinoflagellates exhibit mixotrophic behavior, allowing them to adapt to varying
nutrient availability.
B. Based on the size, planktons are the following type:
1. Macro-planktons: The larger group of planktons that are visible to the naked eye. They occupy
more than 2 mm in size. Examples: Ctenophores, salps, Mysis larva, nymph and amphipods.
2. Meso-plankton: The plankton of middle depths below the penetration of photosynthetically
effective light. Planktons bearing a group length of 200 𝝁m to 2 mm are included in this type.
Examples: Ostracoda, Chaetognaths, Pteropoda, and Tunicata.
3. Micro-plankton: Their size varies from 20 to 200 𝝁m, e.g. Copepods, most of the phytoplankton,
protozoans and large protists.
4. Nano-plankton: Size ranges from 2 to 20 𝝁m, e.g. Protists, Diatoms and Algae.
5. Ultranano-plankton: Very minute planktons with 0.5 to 2 𝝁m in size. Examples: Juvenile
stages of some protozoans.
C. Based on Ecology:
1. Limnoplankton: Limnoplankton refers to planktonic organisms living in lakes. Examples:
Daphnia (water fleas), Rotifers, Fragilaria and various species of freshwater algae.
2. Rheoplankton: Rheoplankton are planktonic organisms that inhabit flowing waters, such as rivers
and streams. They are adapted to survive in environments with significant water movement.
Examples: Examples include certain types of diatoms, phytoplankton like Melosira and small
crustaceans that can withstand currents, like some species of copepods.
3. Heleoplankton: Heleoplankton (uncountable) are planktons that live in still freshwater such as
ponds and marshes. E.g., Euglena.
4. Helio-plankton: Plankton living in marine water. E.g., Chaetoceros.
5. Hypalmyroplankton: Planktons living in brackish water are called hypalmyroplanktons. E.g.,
Chaetophora.
