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Difference between Phytoplankton and Zooplankton

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Phytoplankton Definition

Phytoplankton, a group free-floating microalgae, is an important component of freshwater, ocean and sea ecosystems.

Two Greek words are responsible for the term phytoplankton: Phyto, which means plants, and plankton, which means drifter. Because phytoplanktons are self-sufficient, they also receive chlorophyll, which is similar to land vegetation. Because phytoplankton require sunlight to grow, they are often found floating on top of water bodies. Although individual phytoplanktons can’t be seen by the naked eye, when they are present in large numbers, they can be seen as colored spots on the water surface. About 1% of all the world’s total biomass is made up of phytoplankton. These organisms provide the main source of food for many marine and freshwater species.

Seasonal variations in phytoplankton may occur depending on the availability of sunlight, temperature and other substrates. Diatoms, cyanobacteria and dinoflagellates are just a few of the many groups that make up phytoplankton. These organisms use various inorganic minerals to photosynthesise which then converts them into carbohydrates, proteins, and other nutrients. The phytoplankton is a diverse group of organisms that includes protistan and archaeal prokaryotes, as well as bacterial prokaryotes. Half of the global photosynthetic activity is accounted for by phytoplankton, which is also the main producer in freshwater and marine food chains.


They are the main food source for aquaculture and mariculture, and can even be used as a nutritional supplement to various invertebrates in aquaria. Alga blooms can form when phytoplanktons grow excessively if there are not enough nutrients. These alga blooms can produce toxic and harmful substances that could cause harm to the habitat’s ecosystems. According to studies that were conducted between 2015 and 2019, the phytoplankton level has been decreasing by approximately 1% each year due to global warming. Diatoms, green algae, cyanobacteria and coccolithophores are some examples of phytoplankton.

Examples of phytoplanktons


Cyanobacteria, a photosynthetic bacteria found mostly in water, use sulfur compounds to produce their food via chemical synthesis. Blue-green algae are also known as Cyanobacteria, because they are autotrophs. They are responsible for the majority of oxygen in marine environments. They are a large group in phytoplankton, and they are evenly distributed throughout all water bodies around the globe. There are many types of cyanobacteria. Cyanobacteria can thrive in extreme environments due to their superior resistance to phytoplanktons.

They are found in colonies that consist of unicellular colonies to filamentous colonies scattered randomly throughout water bodies. Different biomasses can be formed as colonies separate to form different types of colonies. Some cyanobacteria like Lyngbya might even form blooms. Like all phytoplanktons and cyanobacterias, zooplankton can rely on cyanobacteria for food. Synechocystis and Oscillatoria are some examples of cyanobacteria that can be found in oceanic habitats. Lyngbya is another example.


These unicellular organisms appear golden-brown because of the presence golden-brown-colored plastids. Dinoflagellates have a close symbiotic relationship. They take in inorganic minerals and provide them with enough oxygen. They have a dented cell membrane, distinct swimming patterns, and a large nucleus. Dinoflagellates is the name given to them because they have two distinct flagella that protrude from their cell membrane.

They are an important part of phytoplanktons, which produce food and oxygen for our environment. However, they can be dangerous if they become blooms. Some dinoflagellates can even cause harm to other animals or plants that share the habitat. Dinoflagellates can include Oxyrhis marina and Symbiodinium.

Zooplankton Definition

Zooplankton is a group of small and floating organisms that form most of the heterotrophic animals in oceanic environments.

The term zooplankton comes from two Greek words ‘zoo’ meaning animals and ‘plankton’ meaning drifter. Zooplanktons form an integral part of food chains in aquatic environments from freshwater to seas and oceans. Because zooplanktons are heterotrophs, they depend on the phytoplankton and other autotrophs for their energy and carbon source. Their movement, along with water allows them to find food and also protect themselves from predators.

Zooplanktons include animals of various sizes ranging from small protozoans to large metazoans. Other animals like young starfish and worms might also act as temporary zooplanktons. Zooplanktons, like phytoplanktons, have multiple groups of animals, including radiolarians, foraminiferans, and dinoflagellates, cnidarians, crustaceans, chordates, and molluscs. Most zooplanktons are larval forms of fishes and invertebrates that later undergo metamorphosis to change into full-fledged sea creatures.

The distribution of zooplankton is limited due to various factors like predation, competition, and breeding. Additionally, patches of zooplanktons are seen in areas with adequate physical conditions like temperature, water currents, and salinity. The number of zooplankton is also limited by the presence of phytoplankton which, in turn, might be disturbed by various other factors, including their lifecycle. Zooplanktons are an essential part of ocean food chains as they function as a source of food for higher consumers like fishes.

These are an important group of animals as they might even function as a conduit for the packaging of organic materials in the biological bumps. They also act rapidly against the increasing number of phytoplankton, resulting in blooms, preventing their harmful effects. Some zooplanktons have also been associated with the removal of toxic materials like mercury from the pollutants in the water. However, zooplanktons also support the survival and transfer of various diseases by housing the pathogenic agents.

Bacteria like Vibrio cholerae exist in a symbiotic relationship with crustacean zooplanktons as the exoskeleton of such animals provides carbon and nitrogen necessary for the bacterium. Some examples of zooplanktons include animals like radiolarians, krill, jellyfish, young molluscs, amphipods, among others.

Examples of zooplanktons


Jellyfish is a type of zooplankton capable of swimming and drifting through oceans. Nearly all oceans are home to jellyfishes. They all belong to the same group as corals and sea anemones. Jellyfish have transparent, soft-bodied bodies that look like an umbrella with tentacles hanging from the edges. This structure is known as the medusa. Jellyfish can range in size from microscopic to more than one meter long.

Zooplanktons such as jellyfish are an important link between phytoplankton, higher animals and ocean food chains. The problem might be that jellyfish are becoming larger than normal, as large jellyfish can eat larvae from small fishes.


Krill is an important component of zooplanktons, a type crustacean that can be found in oceans around the globe. Krill can be found in the water’s surface during the day but move to the deeper parts at night. They are often a lower trophic level primary consumers, which acts as a bridge between phytoplanktons or secondary or tertiary buyers. Krill is a major food source for larger marine mammals.

They can even be fished commercially because they are suitable for use as food in aquaculture or mariculture. They have a transparent, chitinous exoskeleton that is similar to other crustaceans. Krill have organs called photophores, which can emit light. This is possibly useful for orientation and mating.

Difference between Phytoplankton and Zooplankton – Phytoplankton vs Zooplankton

Basis for ComparisonPhytoplanktonZooplankton
DefinitionPhytoplankton, a group free-floating microalgae, is an important component of freshwater, ocean and sea ecosystems.Zooplankton refers to a small group of floating organisms that make up most heterotrophic animals found in oceanic environments.
TermsPhyto is a term that refers to ‘plant like’.“Zoo” refers to “animal-like”.
Consists OfDiatoms, cyanobacteria and dinoflagellates are the main components of phytoplanktons.The Zooplanktons include organisms such as radiolarians and foraminiferans and dinoflagellates and dinoflagellates.
NutritionPhytoplanktons can produce their own food using sunlight and chlorophyll.The distribution of phytoplankton is a key factor in heterotrophic Zooplanktons.
HabitatBecause phytoplanktons require sunlight to photosynthesis, they are most often found floating on the surface waters.The darkest and deepest areas of the water are home to Zooplanktons.
AppearancePhytoplanktons can be described as greenish patches of water. They can also appear brown.Although zooplanktons are mostly transparent, their size, shape, and color may vary depending on the species.
SizePhytoplanktons can be invisible to unaided eyes, and are only visible as green patches when they are present in large quantities.Many zooplanktons can be seen naked by most of them.
PhotosynthesisPhotosynthesis is possible in phytoplanktons, which are responsible for approximately half of all photosynthesis worldwide.The photosynthesis ability of Zooplanktons is not possible.
Oxygen releasePhytoplanktons, which are photosynthetic, are vital for oxygen release.Zooplanktons take in oxygen, but don’t produce it.
EnergyPhotosynthesis is the process by which phytoplanktons get their energy from inorganic minerals.Zooplanktons get their energy from phytoplankton.
Position in food chainThe oceanic food chains are produced by phytoplanktons.The primary and secondary consumers of oceanic food chains are Zooplankton.
MovementMany phytoplanktons cannot freely move with water currents.The ability to move with or against currents is a characteristic of Zooplanktons, which can be used against predators and competitors.
MetamorphosisMetamorphosis is not possible in phytoplanktons.Most zooplanktons begin life as larvae of fishes or invertebrates and then metamorphose into free-swimming organisms.
Vertical migrationVertical migration is not possible for phytoplanktons.Vertical migration is possible in water for Zooplanktons.
FunctionsPhytoplanktons are food for zooplankton as well as indicators of the health and condition of marine environments.The indicators of toxic substances in ecosystems are Zooplanktons. They also provide food for higher heterotrophs.
ExamplesDiatoms, green algae, cyanobacteria and coccolithophores are some examples of phytoplankton.There are many examples of zooplanktons, including radiolarians and jellyfish, young Molluscs, amphipods, and even radiolarians.


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