Difference Between Phytoplankton and Zooplankton

The term ‘plankton’ comes from a Greek word that means “wanderer” or “drifter,” which refers to the tiny species that float along ocean currents and drift along in bodies of fresh water.

Zooplankton and phytoplankton are the two types of plankton found in the oceans. Even though they live in the same waterbody, have identical size, and are both vital to the marine environment, the two different forms of planktons have distinct characteristics. 

Phytoplankton vs Zooplankton

The main difference between phytoplankton and zooplankton is that phytoplanktons are plants, whereas zooplanktons are animals. A typical example of phytoplankton is algae or diatom, and an example of zooplankton are crustaceans such as krill. These two planktons usually float on the water’s surface. 

Phytoplankton vs Zooplankton

Phytoplankton is free-flowing autotrophic plankton. It is often referred to as microalgae. They can be either photosynthetic planktons or chemosynthetic algae and are found in both marine habitats as well as freshwater. Phytoplanktons are the major producers of the oceanic environment. Two major types of phytoplanktons are dinoflagellates and diatoms.

Zooplankton is a group of floating organisms. They are heterotrophic in nature and are found in both fresh water and marine habitats. They are mostly found in lower regions of the water body. Zooplanktons are basically the consumers that feed on phytoplankton. The two major types of zooplanktons are holoplankton and meroplankton.

Comparison Table Between Phytoplankton and Zooplankton

Parameters of ComparisonPhytoplanktonZooplankton
MeaningPhytoplankton is a free-floating plant-like structure that is present on the water’s surface.Zooplankton is an animal-like group of organisms that are free-floating on water’s surface.
AppearanceIt looks like cloudy patches when in place, green-colored to brown color.These are mostly transparent. Found in varying shapes and sizes.
Found inFound on the water surface as they require sunlight.  Found in deeper and darker regions of the ocean, away from sunlight.
Mode of nutritionThey produce their food by photosynthesis or chemosynthesis. They are autotrophic.They depend on phytoplankton and other zooplankton. They are heterotrophic.
FunctionsThey act as food for zooplankton and helps in the indication of marine health (e.g., in the case of red tides).  They act as food for higher heterotrophs. Helps in the indication of the presence of the toxic substance in the marine environment.
PhotosynthesisPhytoplanktons are capable of photosynthesis.Zooplanktons are incapable of photosynthesis.
EnergyPhytoplanktons get energy by means of photosynthesis.Zooplanktons get their energy by feeding on other planktons.
Food chain supply positionPrimary producersPrimary or secondary consumers
ExamplesCyanobacteria, Blue-green algae, diatoms, dinoflagellates, and coccolithophoresMeroplankton, crustaceans (krill), mollusks, holoplankton, chordates, radiolarians,  protozoans, and foraminiferans

What is Phytoplankton?

Phytoplankton is free-flowing autotrophic plankton and is often also known as microalgae. They can be either photosynthetic planktons or chemosynthetic algae. They can be found in both marine habitats as well as freshwater. Chemosynthetic phytoplanktons are found in deeper oceans and use inorganic substances. Photosynthetic phytoplankton is found on the surface of the water body as they require sunlight. Two major types of phytoplanktons are dinoflagellates and diatoms.

Phytoplanktons are photosynthetic plants as obtain energy through the process of photosynthesis and take up nutrients from their surrounding environment. Phytoplankton serves as food for many types of marine species ranging from larvae to big fishes. They are affected by even the smallest of the change in the marine environment, such as changes in temperature, nutrient change in the environment, and are used as indicators of water health. One such case is red tide. Red tide occurs due to the overgrowth of specific harmful algae, which leads to the release of toxins, causing the death of marine species.

They are tiny microorganisms and cannot be seen by our naked eye, but they appear cloudy when present in masses. Phytoplankton constitutes approximately 1% of the world’s total biomass. They act as food supplements for most marine and freshwater supplements. The phytoplankton amount can vary according to the available sunlight, temperature, nutrients, and many other factors. Some of the examples are diatoms, cyanobacteria, dinoflagellates, coccolithophores.

What is Zooplankton?

Zooplankton is a group of floating organisms, heterotrophic in nature, found in both fresh water and marine habitats. They are mostly found in lower regions of the water body. Zooplanktons get their energy by feeding on phytoplankton, other bacteria, plant parts, and other zooplanktons. The two major types of zooplanktons are holoplankton and meroplankton.

Zooplanktons are often found in deeper parts or in the middle parts of the oceans as they do not require sunlight and tend to travel to the surface for feeding and also in order to escape their predators. They are found all over the world in oceans and in freshwater bodies such as lakes, ponds, etc. Zooplanktons are a crucial part of the food chain and act as primary or secondary consumers.

They include many species ranging from small protozoans to a variety of metazoans. Some of the typical examples of zooplanktons are meroplankton, crustaceans such as krill, mollusks, chordates, radiolarians, jellyfish, protozoans, and foraminiferans. They are found in regions with the appropriate temperature, salinity, and water currents. 

Main Differences Between Phytoplankton and Zooplankton

  1. Phytoplanktons are free-flowing plants, while zooplanktons are free animals. 
  2. Phytoplanktons are autotrophic, either photosynthetic or chemosynthetic, while zooplanktons are heterotropic.
  3. Phytoplanktons are primary producers, while zooplanktons are primary consumers. 
  4. Phytoplanktons are found on the surface of the water body, while zooplanktons are found on both surfaces as well as the interior of the water body.
  5. Phytoplanktons prepare their food, i.e., They are capable of photosynthesis while zooplanktons are not.


Phytoplankton and zooplankton are plant and animal species found in the marine environment. While phytoplanktons are autotrophic and prepare their own food, zooplanktons are heterotrophic and are dependent on phytoplankton and other zooplanktons for their food.

Phytoplankton and zooplankton are important to maintain the balance of the ecosystem. Phytoplankton is also one of the major producers of oxygen and is important to maintain oxygen levels in the marine environment. They also serve as natural indicators for algal bloom and increased toxicity. Both can be found in oceans all over the world and in some freshwater bodies. 


  1. https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.1996.41.7.1572 
  2. https://www.nature.com/articles/nature02593 

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