Phytoplankton Vs Zooplankton: Definition, 16 Differences, & Examples

Phytoplankton Vs Zooplankton: An Overview

Phytoplankton Definition

The free-floating microalgae known as phytoplankton play a significant role in the ecosystems of the ocean, sea, and freshwater bodies of water.

  • The terms “phyto” and “plankton,” which both imply drifter in Greek, are combined to form the word “phytoplankton.”
  • Since phytoplanktons get chlorophyll to produce their own nourishment, they are autotrophic, much like terrestrial plants.
  • The majority of phytoplankton are seen floating on the surface of bodies of water because they need sunshine to prepare their meal.
  • Although phytoplanktons are so small that an unaided eye cannot detect them, they are visible as colorful patches on the water’s surface when they are present in large numbers.
  • About 1% of the world’s biomass is made up of phytoplankton. The majority of freshwater and marine creatures eat these organisms as their main source of nutrition.
  • Depending on different substrates, temperature, and the availability of adequate sunshine, phytoplankton concentrations may vary.
  • Diatoms, cyanobacteria, dinoflagellates, green algae, and other different species make up phytoplankton.
  • During photosynthesis, these creatures use a variety of inorganic minerals to produce proteins, carbohydrates, and other nutrients for themselves and other animals.
  • In contrast to other autotrophs like plants, phytoplankton is made up of a variety of different types of organisms, from bacterial or archaeal prokaryotes to protistan eukaryotes. 
  • Half of all photosynthetic activity on Earth is accounted for by phytoplankton, which is also the main contributor to the marine and freshwater food webs.
  • These are the main food sources in aquaculture and mariculture and are also used as dietary supplements for different invertebrates in aquariums.
  • When nutrients are present in excessive numbers, phytoplankton may grow out of control, developing algae blooms.
  • These blooms might create poisonous or even lethal compounds that could disrupt the habitat’s other ecosystems.
  • Based on research done between 2015 and 2019, it was shown that global warming is causing the phytoplankton concentration to drop by around 1% per year.
  • Diatoms, green algae, cyanobacteria, and coccolithophores are a few examples of phytoplankton.
Phytoplankton Vs Zooplankton
Image Credit: Biodifference

Zooplankton Definition

Most of the heterotrophic creatures in marine settings are composed of tiny, floating organisms known as zooplankton.

  • The name “zooplankton” is derived from the Greek terms “zoo,” which means “animals,” and “plankton,” which means “drifter.”
  • In aquatic ecosystems ranging from freshwater to seas and oceans, zooplankton plays an essential role in food chains.
  • As heterotrophs, zooplankton rely on phytoplankton and other autotrophs as a source of energy and carbon.
  • They can locate food and defend themselves from predators thanks to mobility and water.
  • Small protozoans and large metazoans are only a few examples of the creatures that make up zooplanktons. Other creatures, such as immature starfish and worms, may also serve as transient zooplanktons.
  • Like phytoplankton, zooplankton species include cnidarians, crustaceans, chordates, mollusks, radiolarians, foraminiferans, and dinoflagellates.
  • The majority of zooplankton are the larval stages of fish and invertebrates that eventually go through metamorphosis to become mature marine animals.
  • Predation, competition, and breeding are a few of the reasons that limit the dispersal of zooplankton.
  • Furthermore, patches of zooplankton can be found in places with favorable environmental factors such as salinity, temperature, and water currents.
  • The existence of phytoplankton also restricts the amount of zooplankton, and phytoplankton can have their life cycle interrupted by other variables.
  • Zooplankton serves as a food source for higher consumers like fish, making them a crucial component of ocean food chains.
  • They may even serve as a conduit for the packing of organic elements in the biological bumps, making this group of creatures significant.
  • They also quickly counteract the growing phytoplankton population, causing blooms and halting the negative impacts.
  • Some zooplankton has also been linked to removing hazardous substances like mercury from water pollution.
  • However, by hosting harmful organisms, zooplanktons also aid in the survival and spread of many illnesses.
  • A symbiotic connection exists between bacteria like Vibrio cholerae and crustacean zooplanktons because the exoskeleton of these animals provides the carbon and nitrogen that the bacteria need to survive.
  • Animals like radiolarians, krill, jellyfish, immature mollusks, and amphipods are some examples of zooplankton.

Key Differences (Phytoplankton Vs. Zooplankton)

Basis for Comparison Phytoplankton Zooplankton
Definition Phytoplankton is a group of free-floating microalgae that drifts with the water current and forms an important part of the ocean, sea, and freshwater ecosystems. Zooplankton is a group of small and floating organisms that form most of the heterotrophic animals in oceanic environments.
Terms ‘Phyto’ refers to ‘plant-like.’ ‘Zoo’ refers to ‘animal-like.’
Consists of Phytoplanktons consist of diatoms, cyanobacteria, dinoflagellates, green algae, and coccolithophores. Zooplanktons consist of organisms like radiolarians, foraminiferans, dinoflagellates, cnidarians, crustaceans, chordates, and mollusks.
Nutrition Phytoplanktons are autotrophic and, thus, can make their own food with sunlight and chlorophyll. Zooplanktons are heterotrophic, depending on the distribution of phytoplankton for their food and energy.
Habitat Phytoplanktons are found mostly floating on the surface of water bodies as they require sunlight for photosynthesis. Zooplanktons remain mostly around the dark and deeper areas of water.
Appearance Phytoplanktons are seen as cloudy green patches on water. Otherwise, they appear brown in color. Zooplanktons are mostly translucent, but their shape, size, and color might differ with the type of the organism.
Size Phytoplanktons are invisible to the unaided eyes and can only be seen as green patches when present in large numbers. Most zooplanktons are large enough to be seen with the naked eye.
Photosynthesis Phytoplanktons are capable of photosynthesis, being responsible for about half of the photosynthesis performed around the world Zooplanktons are not capable of photosynthesis.
Oxygen release Phytoplanktons are photosynthetic and thus are extremely important for oxygen release. Zooplanktons only take in oxygen and do not produce it.
Energy Phytoplanktons obtain their energy via photosynthesis by utilizing inorganic minerals. Zooplanktons obtain their energy by feeding on phytoplankton.
Position in the food chain Phytoplanktons are the producers of oceanic food chains. Zooplanktons are the primary or secondary consumers of the oceanic food chain.
Movement Most phytoplanktons are not capable of freely moving with water currents. Zooplanktons are capable of moving with or against water currents against predators or competitors.
Metamorphosis Phytoplanktons do not undergo metamorphosis. Most zooplanktons are larval forms of fishes and invertebrates that eventually metamorphose to form free-swimming creatures.
Vertical migration Phytoplanktons are not capable of vertical migration. Zooplanktons are capable of vertical migration in water.
Functions Phytoplanktons act as food for zooplankton and as indicators of the health of the marine environments. Zooplanktons are the indicators of toxic substances present in the ecosystems and also serve as food for higher heterotrophs.
Examples Some examples of phytoplankton include diatoms, green algae, cyanobacteria, and coccolithophores, among others. Some examples of zooplanktons include animals like radiolarians, krill, jellyfish, young mollusks, and amphipods, among others.

Examples of Phytoplanktons

1. Cyanobacteria

  • Cyanobacteria are photosynthetic bacteria that are mostly found in water and use sulfur compounds to chemosynthesis their food.
  • Since cyanobacteria are autotrophs and create most of the oxygen in marine settings. They are also known as blue-green algae.
  • These make up a sizable subgroup of phytoplankton and are dispersed evenly over all the world’s water bodies. Additionally, cyanobacteria come in various forms, dimensions, and hues.
  • Since they are more resilient than other phytoplanktons and can thus endure even harsh aquatic settings, most cyanobacteria are well-suited for various aquatic environments.
  • These are primarily found in colonies made up of filamentous or unicellular colonies that are dispersed randomly throughout water bodies.
  • Different biomasses are created in distinct regions when the colonies divide from each other to occupy different sites. Lyngbya, for example, has the potential to produce flowers.
  • Like other phytoplanktons, cyanobacteria are a source of food for zooplankton.
  • Oceanic ecosystems are home to cyanobacteria like Synechocystis, Oscillatoria, Lyngbya, etc.

You may also like to read: Biotic Factors

2. Dinoflagellates

  • These unicellular creatures have golden-brown plastids, which give them their golden color.
  • The majority of dinoflagellates coexist harmoniously with one another by consuming inorganic minerals and giving them enough oxygen.
  • They feature a dented cell membrane, characteristic swimming patterns, a sizable nucleus, and chromosomes that can be seen.
  • They are known as dinoflagellates because of the two different flagella that protrude from their cell membrane.
  • Despite being an essential component of phytoplanktons that help the ecosystem by providing food and oxygen, they might be dangerous if they grow into blooms.
  • Some of them even release poisonous compounds that are damaging to nearby plants and animals.
  • Dinoflagellates include organisms including Oxyrrhis marina, Symbiodinium, and Dinophysis acuminate.

Examples of Zooplanktons

1. Jellyfish

  • An example of zooplankton that can swim and float through oceans is the jellyfish.
  • Nearly every area of the water is home to hundreds of jellyfish, which are all members of the sea anemone or coral family.
  • Jellyfish have soft, translucent body that resembles an umbrella and are surrounded by tentacles that dangle off of them. The structure is known as the medusa.
  • Jellyfish may be as small as microscopic organisms or as large as one meter in length.
  • Zooplanktons like jellyfish serve as a connection between phytoplankton and higher animals since ocean food chains are often shorter than those on land.
  • However, the fact that there are more of these jellyfish than usual might potentially be a concern because some of them are large enough to eat the larvae of small fish.

2. Krill

  • Krill is an essential component of zooplanktons, a type of crustacean found in oceans all over the world.
  • During the day, krill may be seen on the water’s surface; but at night, they migrate deeper into the ocean.
  • These are often primary consumers at a lower trophic level, acting as a link between phytoplankton and secondary or tertiary consumers.
  • The majority of krill serve as food for bigger marine species.
  • Since they may be utilized as food for aquaculture and mariculture, some of them are even caught for commercial purposes.
  • They have a chitinous exoskeleton that is primarily transparent, like most crustaceans.
  • Krill are bioluminescent creatures with light-emitting photophores that may be crucial for direction and mating.


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