phytoplankton
noun
phy·to·plank·ton
ˌfī-tō-ˈplaŋ(k)-tən 
-ˌtän
plural phytoplankton also phytoplanktons
: minute aquatic photosynthetic organisms (such as dinoflagellates, diatoms, and cyanobacteria) : photosynthetic plankton of freshwater or marine environments
Twenty to 40 different species of phytoplankton … can coexist within a single cubic centimeter of water, all vying just for light and a handful of nutrients.—
O. Baker
O. BakerPhytoplankton—myriad small, mostly unicellular algae and bacteria that occupy the surface waters of seas and lakes—dominate aquatic primary production, and over time they have radically altered Earth's atmosphere.—Robert Riding
Robert RidingPhytoplankton form the foundation of marine food chains, and their seasonal blooms are responsible for more than half the photosynthesis, and the resulting production of oxygen, that occurs on Earth.—Robin George Andrews
Robin George AndrewsAntarctic krill are thumb-sized crustaceans that feast on drifting phytoplankton …—Usha Lee McFarling
compare zooplankton
Usha Lee McFarlingExamples of phytoplankton in a Sentence
Recent Examples on the Web
The culprit, the paper suggests, is the teeny tiny plant-like creatures that form the building blocks of the marine food web — phytoplankton.
—Alex Harris, Miami Herald, 19 June 2025
Where phytoplankton are absent, the water appears blue.
—Julia Jacobo, ABC News, 19 June 2025
The scientists observed that the phytoplankton in the region tend to be iron-deficient during the spring and that a surge in iron supply boosts their seasonal bloom.
—Sharon Udasin, The Hill, 2 June 2025
This is important because phytoplankton are the beginning of the food chain in the ocean and help sequester significant amounts of carbon.
—Leah Sarnoff, ABC News, 4 June 2025
See All Example Sentences for phytoplankton
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Alex Harris, Miami Herald, 19 June 2025
Where phytoplankton are absent, the water appears blue.
—Julia Jacobo, ABC News, 19 June 2025
The scientists observed that the phytoplankton in the region tend to be iron-deficient during the spring and that a surge in iron supply boosts their seasonal bloom.
—Sharon Udasin, The Hill, 2 June 2025
This is important because phytoplankton are the beginning of the food chain in the ocean and help sequester significant amounts of carbon.
—Leah Sarnoff, ABC News, 4 June 2025
See All Example Sentences for phytoplankton
Cite this Entry
“Phytoplankton.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/phytoplankton. Accessed 8 Jul. 2025.
Copy CitationKids Definition
phytoplankton
noun
phy·to·plank·ton
ˌfī-tō-ˈplaŋ(k)-tən
-ˌtän
: plankton that is composed of plants
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