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Zooplankton Meaning

Zooplankton are small animals in the planktonic community. These microorganisms are heterotrophic aquatic organisms. In Greek, "zoo" comes from "anima" and "plankton", which means wanderer, drifter, or wanderer. Even though some of them are larger, they are typically microscopic.

Biochemically, zooplankton are heterotrophic planktonic organisms ranging in size from microscopic organisms to large creatures. These organisms drift in aquatic ecosystems and are ecologically significant drifting organisms. The presence of these small animals in the water column of all water bodies is crucial to maintaining the food chain. Although they are rare in rivers and streams, they can be found in lakes, ponds, and oceans.


A few millimetres to a few microns is the size of these organisms (1 micron is 1/10000 of a millimetre).


The main transport mechanism for zooplankton species is ambient water currents. In some cases, locomotion is used to either avoid predators or increase the rate at which prey is encountered.

Zooplankton Classification

There are two ways to group zooplankton: by size and by developmental stage.

Zooplankton Classification by Size

  • Picoplankton: Zooplankton that is no larger than 2 micrometres.

  • Nanoplankton: This category consists of zooplankton that is between 2 and 20 micrometres in size

  • Microplankton: A form of zooplankton with a size range of 20-200 microns.

  • Mesoplankton: This category includes zooplankton between 0.2 and 20 millimetres in size.

  • Macroplankton: Animals between 20 and 200 millimetres in size.

  • Megaplankton: Populations of zooplankton that measure over 200 millimetres in size, or about 8 inches in length.

Zooplankton Classification Based on Their Developmental Stages

  • Meroplankton: Meroplankton is zooplankton when it is in larval form. Over time, they metamorphose into molluscs, corals, fishes, insects, echinoderms, and crustaceans.

  • Holoplankton: Zooplanktons that remain planktonic throughout their lives. Pteropods, larvaceans, copepods, chaetognaths, and siphonophores are examples of these organisms.

Distribution of Zooplankton

  1. Radiolarians

  2. Dinoflagellates

  3. Foraminiferans

  4. Crustaceans

  5. Molluscs

  6. Cnidarians

  7. Chordates

  • Radiolarians: As well as radiolarians, there are radiozoa. Protozoans that produce mineral skeletons made of silica are small, 0.1-0.2 mm in diameter. Globally, this type of zooplankton is found in all oceans. Ocean bottoms often contain the skeletal remains of these organisms.

  • Dinoflagellates: In the distribution of zooplankton, these are very few in number. Because they are photosynthetic or ingest other species, they are considered mixotrophic species. Dinoflagellates account for a significant proportion of marine eukaryotes and are essential to coral reef health.

  • Crustaceans: Organisms of this type are arthropods. Barnacles, crabs, krill, and shrimp are among them. A significant part of the food chain they are a variety of sizes. The zooplanktonic species krill and copepods are especially important among crustaceans.

  • Molluscs: A wide variety of organisms makes up the molluscs. Octopuses, squids, sea snails, and sea slugs are some of the species found in these waters. The larvae stage of these organisms is usually zooplanktonic.

  • Cnidarians:They are members of the phylum Cnidaria, which includes colonial siphonophores and scyphozoans (true jellyfish). Their stinging tentacles make them predators. Most of these creatures live in the ocean nearer to the surface of the water and are seldom found in freshwater.

  • Chordates:An animal that has a notochord, pharyngeal slits, a hollow nerve chord on the dorsal side, and a post-anal tail is called a chordate. This distribution of zooplankton has a large variety of forms and functions.

Zooplankton Diagram

(Image Will be Updated Soon)

Zooplankton Examples

  • Krill

  • Jellyfish

  • Aquatic sowbug or water louse

  • Segmented worm

  • Portuguese man o’ war

  • Calamus finmarchicus

  • Ostreopsis ovata

  • Blue button (Porpita porpita)

  • Acartia tonsa

  • Forams

  • Acartia clausi

  • Paracalanus parvus

  • Common pill-bug

  • Ligia exotica

  • Common rough woodlouse

  • Giant isopod

  • Anchor worms

  • Air fern

  • Talitres saltator

  • Common salp

  • Pacific sea nettle

  • Ligia oceanica

  • By-the-wind sailor

  • Flying spaghetti monster (Bathyphysa conifer)

What are the Benefits of Zooplankton?

Zooplankton plays an important role in the food web of water bodies due to their position in the food chain. These factors can have a significant impact on the quality of the water, fish production, algal densities, and nutrient and contamination cycling.

Biomonitoring programs frequently include zooplankton species due to their sensitivity to environmental change. Furthermore, some zooplankton species, such as Mysis, have been intentionally introduced to lakes to increase fish production.

Algal blooms may be controlled by increasing zooplankton grazing because zooplankton feed on algae. Biomanipulation is the process of doing this.

Normally this is accomplished by reducing predation on the zooplankton diagram; their predators, such as planktivorous fish, are either removed directly, or a fish predator, such as a pike, is added. Grazing by zooplankton can prevent eutrophication caused by algal blooms in water bodies.

Difference Between Zooplankton and Phytoplankton




In fresh and marine water, they look like plants

They resemble animals. The majority of them live in water bodies.


A group of them forms cloudy patches of brown colour.

Most of them are translucent and come in various colours and shapes.


Lots of oxygen is liberated by them

Oxygen is consumed by them

Mode of Nutrition

Photosynthesis or chemosynthesis is how they make their food

Zooplankton and phytoplankton they consume

Trophic level

The phytoplankton is a primary producer

Zooplankton are primary or secondary consumers in aquatic food webs.


Cyanobacteria, Blue-green algae, diatoms, and dinoflagellates are typical phytoplankton examples

Krill, meroplankton, protozoa, and holoplankton are all zooplankton species.

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FAQs on Zooplankton

1. What does zooplankton eat?

Ans: Several different feeding strategies are used by zooplankton species to maintain their diversity. Zooplankton, algae, bacteria, and other organisms can be eaten by them. Moreover, they may even serve as parasites, while some Cladocera may graze indiscriminately. Many Copepods, on the other hand, are more selective in their prey selection, selecting zooplankton particles by their size, shape, and taste.

Phytoplanktonic algae and protozoa are predators of zooplankton organisms. Zooplankton populations increase proportionally to phytoplankton populations. Light directly influences phytoplankton populations, which indirectly influences zooplankton populations. Whenever light is abundant, like in boreal or temperate areas, phytoplankton increases, which provides more food for zooplankton, which also increase in numbers. During the spring, when light concentration begins to increase, this phenomenon is observed.

2. Can Zooplankton be considered a producer?

Ans: The zooplanktons do not produce anything; rather, they consume the plankton community like animals. Zooplankton, in turn, provides food for larger secondary consumers such as fish. Phytoplankton, on the other hand, is the producer, not the zooplankton; they are the tiny plants that produce the plankton community.

Bacteria and algae comprise the phytoplankton, which forms the trophic base of aquatic food webs. Green algae, diatoms, dinoflagellates, and cyanobacteria are examples of phytoplankton. Phytoplanktonic organisms provide nutrients and oxygen to other organisms through photosynthesis.

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