Phytoplankton vs. Zooplankton: 16 Differences, Examples

Phytoplankton 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.

• The term phytoplankton comes from two Greek words, ‘Phyto’ meaning plants, and ‘plankton’ meaning drifter.
• Phytoplanktons are autotrophic as, like land vegetation, they are also provided with chlorophyll to make their own food.
• Most phytoplankton are found floating on the top of water bodies as they require sunlight for their food preparation.
• Individual phytoplanktons are tiny and cannot be seen with the unaided eye, but when present in masses, they appear as colored patches on the water surface.
• Phytoplankton makes up about 1% of the total biomass of the world. These organisms are the primary source of food for most marine and freshwater animals.
• The amount of phytoplankton might change seasonally with the availability of sufficient sunlight, suitable temperature, and other substrates.
• There are diverse groups within phytoplankton consisting of diatoms, cyanobacteria, dinoflagellates, green algae and
• These organisms utilize various inorganic minerals during photosynthesis which are then converted into proteins, carbohydrates, and other nutrients for themselves and other animals.
• Unlike other autotrophs like plants, phytoplankton consists of diverse groups of organisms ranging from archaeal or bacterial prokaryotes to protistan eukaryotes.
• Phytoplankton accounts for half of all the photosynthetic activity throughout the world and is the primary producer in the freshwater and marine food chains.
• These are the key food source in aquaculture and mariculture and are even used as a nutritional supplement for various invertebrates in aquaria.
• However, when the nutrients are available in large quantities, phytoplanktons might grow out of control, resulting in the formation of alga blooms.
• These blooms might produce harmful and even toxic substances that might cause damage to other ecosystems within the habitat.
• Based on studies conducted from 2015 to 2019, it was observed that the phytoplankton concentration is decreasing by about 1% every year as a result of global warming.
• Some examples of phytoplankton include diatoms, green algae, cyanobacteria, and coccolithophores, among others.

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.

Key Differences (Phytoplankton vs Zooplankton)

Examples of phytoplanktons

Cyanobacteria

• Cyanobacteria are the photosynthetic bacteria mostly found in water that utilize sulfur compounds to make their food via chemosynthesis.
• Cyanobacteria are also called blue-green algae as they are autotrophs and are responsible for most of the oxygen produced in the marine environments.
• These form a large group within phytoplankton and are distributed uniformly through all water bodies in the world. Cyanobacteria are found in varying shapes, sizes, and colors as well.
• Most cyanobacteria are well suited for various aquatic environments as they are more resistant than other phytoplanktons and thus can survive even extreme aquatic habitats.
• These exist mostly in colonies consisting of unicellular to filamentous colonies distributed randomly through water bodies.
• Different biomasses are formed in different areas as the colonies separate from each other to inhabit different locations. Some cyanobacteria like Lyngbya might even form blooms.
• Cyanobacteria, like all phytoplanktons, serve as a food source for zooplankton.
• Some examples of cyanobacteria found in oceanic habitats include Synechocystis, Oscillatoria, Lyngbya, etc.

Dinoflagellates

• These are unicellular organisms that appear golden-brown due to the presence of golden-brown plastids.
• Most dinoflagellates form a symbiotic relationship with by taking in inorganic minerals while providing them with sufficient oxygen.
• They have a dented cell membrane and show distinct swimming patterns with a rather large nucleus and visible chromosomes.
• They have two dissimilar flagella protruding from the cell membrane, thus, the name dinoflagellates.
• Even though they are important as a part of phytoplanktons in producing food and oxygen for the environment, these might be harmful if developed into blooms.
• Some of them even produce toxic substances harmful to other animals and plants sharing the habitat.
• Some examples of dinoflagellates include Oxyrrhis marina, Dinophysis acuminate, Symbiodinium, etc.

Examples of zooplanktons

Jellyfish

• Jellyfish is an example of a zooplankton that is capable of both drifting and swimming through oceans.
• There are hundreds of jellyfishes residing in almost all parts of oceans, all belonging to the group called sea anemones or corals.
• Jellyfish are transparent and soft-bodied that appears as an umbrella with tentacles around the edges hanging off of them. The structure is called the medusa.
• The size of jellyfish ranges from being microscopic to some being more than one meter in length.
• Because ocean food chains are comparatively shorter than those on the land, zooplanktons like jellyfish form a connecting link between the phytoplankton and higher animals.
• However, the increase in the number of these jellyfish above normal might also be a problem as some large jellyfish can consume the larva of small fishes.

Krill

• Krill form an important part of zooplanktons that are a type of crustacean found populating oceans throughout the world.
• Krill are found on the surface of the water during the day, but they move towards the deeper areas during nights.
• These usually form a lower trophic level as primary consumers that form a bridge between the phytoplanktons and secondary or tertiary consumers.
• Most krill act as a food source for larger marine animals.
• Some of them are even fished commercially as they can be used as a fooder for aquaculture and mariculture.
• Like most crustaceans, they have a chitinous exoskeleton which is mostly transparent.
• Krill are bioluminescent having organs called photophores that can emit light, possibly important for mating and orientation.

References and Sources

• 1% – https://owlcation.com/stem/What-are-phytoplankton
• 1% – https://oceanservice.noaa.gov/facts/phyto.html
• <1% – https://www.vedantu.com/biology/autotrophic-nutrition
• <1% – https://www.thoughtco.com/all-about-photosynthetic-organisms-4038227
• <1% – https://www.encyclopedia.com/plants-and-animals/microbes-algae-and-fungi/moneran-and-protistan/zooplankton
• <1% – https://link.springer.com/chapter/10.1007%2F978-3-642-19106-0_2
• <1% – https://deepoceanfacts.com/deep-ocean-ecosystems
• <1% – https://climatechangeandoceanstratification.blogspot.com/p/importance-of-phytoplanktons.html
• <1% – https://answers.yahoo.com/question/index?qid=20080902141806AAJSDeL
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