What Is Zooplankton? – Zooplankton Meaning

Zooplanktons are animal components of planktons. Planktons are assorted groups of organisms found in water that are unable to swim against the water currents and are hence carried in the direction of the current in seas, oceans, rivers and lakes.

Phytoplanktons, in contrast, are the plant components of planktons. They are autotrophic in nature, meaning they can make their own food. The zooplanktons, on the other hand, are heterotrophic, meaning they must feed on other plants (such as phytoplankton) and animals for nutrition.

Zooplanktons are mostly larger than phytoplanktons. They are microscopic in majority, however some are macroscopic as well (such as jellyfish). Microscopic zooplanktons include protists such as foraminiferans, dinoflagellates, zooflagellates and radiolarians. Macroscopic zooplanktons include ctenophores, molluscs, tunicates, arthropods and cnidarians.

Characteristics

They are heterotrophic planktons that derive their nourishment by feeding on other plants and animals.
Zooplanktons include a large number of organisms ranging from protozoans to metazoans.
The word zooplanktons is derived from the Greek words zoon meaning animals and planktons meaning wanderers or drifters.
They include two types of organisms — holoplanktonic organisms that spend their entire life cycle as planktons and meroplanktonic organisms that spend part of their life cycle as planktons and other parts as benthic, nekton or sessile organisms.
Though zooplanktons are current drifters, they may possess some locomotory motion to to run away from predators or to increase their encounter with preys.
The zooplanktons are distributed in patches all over the ocean. However, their distribution is limited by salinity, temperature, breeding, migration and concentration of phytoplanktons.
They occupy an important place in the aquatic food web by feeding on phytoplanktons and other food resources.
They also play a part in biomagnification of certain pollutants such as mercury.
The example of protozoan zooplanktons include dinoflagellates, zooflagellates and radiolarians.
Examples of important metazoan zooplanktons include jellyfish, Portuguese Man o’ War, molluscs, amphipods and shrimp-like crustaceans.
The zooplanktons feed on phytoplanktons, bacterioplankton, other zooplanktons and nektonic organisms.
They can also be the cause of diseases. The crustacean zooplanktons form symbiotic relationships with Vibrio cholerae that causes cholera.

Classification

The zooplanktons can be classified on the basis of their size. However they differ in their morphology, feeding habits, and diet. The classification is as follows:

Picozooplankton (<2μm)
Nanozooplankton (2-20μm)
Microzooplankton (20-200μm)
Mesozooplankton (0.2-20mm)

Behaviour

The zooplanktons tend to migrate vertically by feeding on the phytoplanktons, around the surface of water. They have adapted different mechanisms to travel in the water and also save themselves from being preyed upon. For example, larval crustaceans have spikes on their body which gives them a larger surface area for floating and also saves them from predators. Some fish larvae have oil globules that add to the buoyancy of the zooplankton.

The zooplanktons are preyed upon by whales, fish and shellfish. They themselves prey upon phytoplanktons, other zooplankton and bacterioplankton.

Importance

Grazing by zooplanktons is a rate-setting process in the aquatic ecosystem and also a driver of aquatic biogeochemical cycles. Grazing by heterotrophic protists results in the single largest loss factor of aquatic primary production and alteration in particle size distribution. Grazing is important for both deep and surface carbon processes.

Apart from linking the primary producers to higher trophic levels in the marine ecosystem, zooplanktons play an important role in recycling of nutrients as well, thus affecting the biogeochemical cycles and the biological pump.

Visit BYJU’S for more information related to NEET.

Frequently Asked Questions

Is zooplankton a plant or animal?

Zooplanktons are animal components of planktonic communities.

Can you see plankton with your eyes?

Yes, while some planktons such as dinoflagellates and radiolarians are microscopic, others such as jellyfish and Portuguese man o’ war are macroscopic and can be seen with naked eyes.