Zooplankton: Characteristics, Types and Their Role in the Aquatic Ecosystem

Ever looked closely in a streams or swamps and thought no living organism there?

Then you’re wrong! 

Look again! You probably will see lots of  tiny plants and animals living there. Some of them you might be able to see floating on the surface, and to see others you need a microscope. These tiny organism are referred to as “plankton.”

The term Plankton comes from the Greek word “planktos” which means drifter or wander. This types of tiny creatures always float or drift on the surface of the water and can’t swim against water current.

Definition of Zooplankton:

Zooplankton means animal plankton that float freely on, or near the surface of any aquatic environment including sea, river or estuaries. These include a vast array of organism, from small microscopic protozoans to the large macroscopic metazoans and even large sea creatures.
They can be seen everywhere, but the most of those live on surface of the water. However, Zooplankton depends on Phytoplnkton which are other types of plankton . Phytoplankton are the the primary food in the food chain for many aquatic animals.

Mainly two types of Zooplanktons are found in the water. Some of these weeny animal spend their whole life in a drifting state which are called permanent plankton. In addition some others are temporary which only spends their larval stage of life as plankton and mature life as fish or any other aquatic animals. When these others types of organism become mature they are not plankton anymore.

For example; Crabs and shellfish

Some other examples of zooplankton are; Jellyfish, Ice fish, Daphnia, and Diaphanosoma.

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  • Zooplankton are key coomponents of an aquatic ecosystems help building the foundation of food webs in the river or sea.
  • Zooplankton totally dependent on sunlight, temperature, turbidity, oxygen and salinity in its environment
  • They work as marker of the aquatic ecosystem.
  • By measuring diversity of species, counting biomass and affluence of zooplankton concentration, the health of the aquatic ecosystem can be determined.

Types of Zooplankton:

Zooplankton is classified into two types based on a development.
Holoplankton and Meroplankton


These types of organism spends their whole life dwelling through the epi pelagic and meso pelagic zones. . That name comes from two Greek words “holo” which means entire and “plankt” that mean drifter. This zooplankton spends their whole life drifting in the sea. That’s why they are called permanent zooplankton. They never be able to swim against water current or tide. Most of the holoplankton are copepods which are vital food source for fish.
Example; diatoms, radiolarians


Meroplanktons are the community of organism that spends early stage of their life as plankton before growing into the adult stage. Greek Word “mero” means portion and these organism spends part of their life in surface of the water and other part of their life on benthic zone. Moreover meroplankton are known as temporary zooplankton. After ending of the planktonic life in transition, they finally become larger species which can swim freely.

Example; sea urchins, starfish

According to the Sizes zooplankton are several Types:

Picoplankton – These are tiny photosynthetic organism formed by cells between 0.2 and 2 µm.
Example; Cyanobacteria, Ostreococcus and Micromonas

Nanoplankton – All zooplankton with more than 2 and less than 20 micrometers fall on this category. They poses nitrogenoous gene which play important role in nitrogen fixation.
Example; Chlorophyta; Xanthophyta, small diatoms.

Microplankton – These includes the organism of size from 20 and no greater than 200 micrometers.
Example; small copepods

Mesoplankton – The planktons which floats bellow 200 meters depth from the surface where sunlight can not reach. Their size varies from 200 micrometers to 20 millimeters

Example; Rhincalanus, Polycheate, Radiolaria Larvea etc.

Macroplankton – The larger planktonic animals includes on this category and size reach between 20 and 200 millimeters
Example; Tunicata, Pteropods

Megaplankton – These are the largest zooplankton generally reach size over 200 millimeters.

Example; jellyfish, krill, sea snails & slugs etc.

What Do Zooplankton Eat?

Zooplankton is the animal plankton who needs to eat something to survive, need nutrition, energy to move throughout the water.
Their primary food is phytoplankton. However, many of the larger zooplankton eats smaller ones. As like as fish and other aquatic community, zooplankton also have diversity based on food they consume. Most Megaplankton are carnivores as they use their teeth to eat and most picoplankton and nanoplankton are herbivores who just eat phytoplankton. Microplankton, mesoplankton and macroplankton are usually omnivorous; feed everything including small plants, deed organic materials and other plankton as well.

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