Phytoplankton - Definition, Types and Importance

Phytoplankton – Meaning

The word phytoplankton is derived from two Greek words – phyton (plant) and planktos (drifter). Planktons are the primary producers (plants) belonging to the planktonic community.

Phytoplanktons are found in all types of aquatic ecosystems and are a food source for many zooplanktons. They are one of the forefront basal organisms in the aquatic food chain. Phytoplanktons are considered to be a rich source of food, biofertilizers, biofuel and feed. They also play a vital role as indicators in monitoring water quality.

Examples of Phytoplankton

Phytoplanktons are a diverse group of photoautotrophic microorganisms. It includes bacteria, algae and some archaebacterial prokaryotes. There are approximately around 5000 species of phytoplanktons discovered till now. Some examples are –

  • Blue-green algae – Synechococcus, Prochlorococcus, Spirulina
  • Green algae – Chlorella vulgaris, Dunaliella salina
  • Diatom – Odontella aurita, Phaeodactylum tricornutum
  • Dinoflagellate – Protoperidinium depressum

Types of Phytoplankton

Based on cell wall arrangement and cell structure, the phytoplanktons are classified into five types –

  1. Diatoms – They are microalgae with characteristic shell-like structure composed of translucent silica. Based on the nature of their valves and ornamentation (markings) in them, they can be grouped into –
    • Centric – These diatoms have a discoid, cylindrical or solenoid cell. Their arrangement of markings radiates from the centre.
    • Pennate – They are ovate, elongated, fusiform, sigmoid or roughly circular. Their arrangement of markings is on either side of the apical axis.
  2. Dinoflagellates – They are unicellulars with two flagella for locomotion. Some of them are naked while some are armoured with plates of cellulose. Also, most dinoflagellates are luminescent.
  3. Blue-Green Algae – They are usually unicellular but can also be seen growing in colonies. The blue colour is due to a pigment called phycocyanin.
  4. Green Algae – They are green coloured due to the presence of chloroplast. They are mostly seen in the coastal water of the tropics and subtropics.
  5. Coccolithophores – They are the smallest phytoplanktons that are commonly seen in the open sea. They have a soft body covered with a tiny, calcified circular shield. Also, some have flagella, while others are devoid of them.

Furthermore, phytoplankton can also be classified based on their size as –

  • Ultraplankton – < 2 µm
  • Nanoplankton – 2 to 20 µm
  • Microplankton – 2 to 200 µm
  • Macroplankton – 200 to 2000 µm
  • Megaplankton – > 2000 µm

Based on habitat, phytoplanktons can be:

  • Neritic – Phytoplanktons inhabiting waters overlying continental shelves
  • Oceanic – They inhabit waters beyond continental shelves
  • Brackish water – They inhabit brackish water areas such as mangroves, estuaries, lagoon, etc.

Economic Importance of Phytoplankton

Phytoplanktons have several uses and their mass cultivation can also be a major source of income. They are mostly used as food supplements and play a vital role in both animal and human nutrition. Phytoplanktons are also used in the manufacture of drugs. Also, they have proven to be suitable for synthesising vaccines. The following table provides a glimpse of the phytoplanktons and their uses:



Chlorella vulgaris

Food supplement, animal feed.


Food supplement and cosmetics

Odontella aurita

Cosmetics, pharmaceuticals and food for both adults and infants

Phaeodactylum tricornutum

Fuel production and nutrition

Porphyridium cruentum

Cosmetics, pharmaceuticals and nutrition

Planktons in Carbon Sequestration

Phytoplanktons are biological sources that can be used for carbon sequestration. Some species of phytoplanktons have a high tolerance to CO2 and can significantly capture carbon. Thus, has a role in reducing global warming. It is discovered that some diatoms can absorb around 10 to 20 billion tonnes of CO2 every year.

Likewise, some phytoplanktons can also sequester pollutants and are used for bioremediation processes. This is called phycoremediation.


Frequently Asked Questions

What is plankton?

The word plankton denotes drifting. Any organism that drifts near or on the water surface and are unable to swim efficiently are called planktons. Most of them drift with water currents. The planktonic community has autotrophs called phytoplanktons and animal components called zooplanktons.

What is the difference between phytoplankton and zooplankton?

Phytoplanktons are plant-like microorganisms that are the primary producers of the aquatic community. Zooplanktons are animal-like tiny organisms that belong to the planktonic community. It also includes the larval phases of some animals. They usually feed on phytoplankton and sometimes even on other zooplanktons.

What are some examples of phytoplanktons?

Phytoplanktons include a variety of microorganisms like algae and bacteria. Examples include Spirulina, Chlorella vulgaris, Odontella aurita, Dunaliella salina, Porphyridium cruentum, etc.

What is a photic zone?

The photic zone or euphotic zone is the uppermost layer of the water body that receives sunlight. The majority of phytoplankton and other aquatic organisms live in this photic zone. Phytoplanktons need a well-lit region like the photic zone to carry out photosynthesis.

Also Check: Difference between Phytoplankton and Zooplankton

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