Zooplankton vs Phytoplankton

Zooplankton vs Phytoplankton

Phytoplankton and zooplankton are two concepts in the field of saltwater aquariums that every enthusiast of marine animals and corals should be familiar with. Read the article and learn about the differences between them.

Table of Contents

What are phytoplankton and zooplankton?

On one hand, phytoplankton and zooplankton are two distinct but, on the other hand, interrelated elements found in marine ecosystems. To better understand how life functions in a marine aquarium, we need to know the differences between phytoplankton (tiny plant organisms) and zooplankton (tiny animal organisms).

Before deciding to use either of them, get to know the fundamental differences between phytoplankton and zooplankton by reading this article to the end.

More information about the significance of phytoplankton and zooplankton in a marine aquarium can be found in separate articles.

Comparison of phytoplankton with zooplankton

Phytoplankton and zooplankton play a significant role in marine aquariums. Phytoplankton provides oxygen and serves as the primary food source for many organisms, while zooplankton transforms this energy and nutrients along the food chain.

Therefore, a balance between phytoplankton and zooplankton is essential to maintain a healthy and stable marine aquarium. An excess or deficiency of either of these elements can lead to disruptions.

The comparison in the table below will help you understand the crucial role that phytoplankton and zooplankton play in saltwater aquariums despite significant differences between them.

  • What are they?

PHYTOPLANKTON: It consists of tiny plant organisms: diatoms, cyanobacteria, dinoflagellates, green algae.

ZOOPLANKTON: It consists of tiny animal organisms: foraminifera, small crustaceans, chordates, and mollusks.

  • Function 

PHYTOPLANKTON: serves as the primary food source for zooplankton and plays a crucial role in oxygen production in the water. It constitutes the first and most important level of the food chain in marine aquariums.

ZOOPLANKTON: provides food for higher-order heterotrophic organisms. Its main function is to transform energy and nutrients derived from phytoplankton and other small organic particles into a form that can be utilized by larger organisms. Zooplankton serves as a direct food source for many species of fish, crustaceans, and other marine creatures

  • Nutritional mode 

PHYTOPLANKTON: Autotrophic mode of nutrition, showing the ability to independently produce essential nutrients for life and development. This process occurs mainly through photosynthesis.

ZOOPLANKTON: Heterotrophic mode of nutrition, obtains nutrients by consuming other organisms or organic products, including phytoplankton. It is unable to independently produce nutrients.

  • Role in the food chain* 

PHYTOPLANKTON: Functions as the primary producers, serving as food for primary consumers, organisms that are unable to photosynthesize and must obtain nutrients externally. Phytoplankton provides energy and nutrients for primary consumers. Primary consumers in aquatic ecosystems are often small animals, such as some species of zooplankton, fish larvae, or small crustaceans, that feed directly on phytoplankton.

ZOOPLANKTON: Occupies the position of either primary or secondary consumers. Primary consumers are organisms that feed directly on phytoplankton, transforming absorbed organic components into energy essential for growth, reproduction, and other life processes. Larger or more specialized species of zooplankton may assume the role of secondary consumers, feeding on smaller animals or other zooplankton.

  • Nutritional value 

PHYTOPLANKTON: Forms the beginning of the food chain for zooplankton and is less diverse than zooplankton. It provides essential substances such as carbohydrates produced in the process of photosynthesis. It is also a source of proteins, lipids, and minerals. However, its nutritional value is limited due to its lower diversity and simpler biological structure.

ZOOPLANKTON: Provides many essential nutrients such as proteins, lipids, vitamins, and minerals. It is more diverse than phytoplankton due to a varied range of nutrients.

  • The ability to carry out photosynthesis 



  • Oxygen production 

PHYTOPLANKTON: Produces oxygen through photosynthesis.

ZOOPLANKTON: Consumes oxygen, lacks the ability to produce oxygen.

  • Activity 

PHYTOPLANKTON: Lacks the ability for active movement. Its movement in the aquatic environment is largely dependent on water currents, waves, and other environmental factors.

ZOOPLANKTON: Can both passively drift and actively move, allowing them to react during predator attacks.

  • Size 

PHYTOPLANKTON: Rarely visible to the human eye. However, their massive populations can sometimes be seen as a discoloration of water, especially during algal blooms.

ZOOPLANKTON: Often visible to the human eye and is larger than phytoplankton.

  • The ability to metamorphose 

PHYTOPLANKTON: Retains their microalgal forms and does not undergo metamorphosis.

ZOOPLANKTON: Often begins as larval stages of fish and invertebrates, ultimately transforming into freely swimming adult individuals.

  • Dosage method in a saltwater aquarium

PHYTOPLANKTON and ZOOPLANKTON: Depending on the manufacturer’s recommendations.


In summary, phytoplankton and zooplankton are integral elements of aquatic ecosystems. While they exhibit significant differences in size, feeding habits, nutritional modes, and functions, together they form a complex life network in marine water. Both types of plankton (phytoplankton and zooplankton) influence nutrient cycling, energy flow, and overall balance in a saltwater  aquarium. It is recommended to use both types of plankton.

* The food chain represents the feeding relationships among different organisms in an ecosystem. Generally, it describes the transfer of energy and matter from producers, such as photosynthetic organisms (e.g., phytoplankton), to consumers, which are organisms that feed on other organisms (e.g., zooplankton).

About author

Picture of Magdalena Metzler

Magdalena Metzler

Privately, I am a mother and a lover of nature and sport. My main interest is quantum chemistry, which hides a whole lot of unsolved mysteries and connections, which is extremely exciting from a scientific point of view.
In my scientific career, I have conducted international projects focused on innovative solutions for many branches of business, e.g. automotive, construction, and now, of course, marine aquaristics.
Working at Reef Factory gave me a passion for marine aquaristics, which I can develop every day, building a chemistry department and creating products that will help aquarists take care of tanks and ensure the highest safety of animals. One of the most exciting memories of working at Reef Factory is the commissioning of the ICP-OES spectrometer, which analyzes the elemental composition of seawater. The method of analysis in ICP is based on an analytical technique, which is a combination of my passion for quantum chemistry and marine aquaristics.
I hope you find my articles on ReefPedia interesting and helpful! Happy reading :))