phytoplankton

American  

[fahy-tuh-plangk-tuhn] / ˌfaɪ təˈplæŋk tən /

noun

1. the aggregate of plants and plantlike organisms in plankton.

---

phytoplankton British  

/ ˌfaɪtəˈplæŋktən, ˌfaɪtəplæŋkˈtɒnɪk /

noun

1. the photosynthesizing organisms in plankton, mainly unicellular algae and cyanobacteria Compare zooplankton

---

phytoplankton Scientific  

/ fī′tō-plăngk′tən /

1. Plankton consisting of free-floating algae, protists, and cyanobacteria. Phytoplankton form the beginning of the food chain for aquatic animals and fix large amounts of carbon, which would otherwise be released as carbon dioxide.

---

Other Word Forms

• phytoplanktonic adjective

Etymology

Origin of phytoplankton

First recorded in 1895–1900; phyto- + plankton

Explanation

Tiny plants that live near the surface of the ocean and are too small to see are phytoplankton. Many small sea creatures, like krill, feed on phytoplankton. Yum! The word phytoplankton comes from Greek roots: phyton, "plant," and planktos, "wandering or drifting." Much plankton is composed of tiny animals, but the plankton made up of plants is phytoplankton. These microscopic organisms drift along close enough to the ocean's surface to photosynthesize, absorbing light and making their own food. Phytoplankton are an important part of the food chain — they're eaten by krill, which are eaten by baleen whales.

Example Sentences

Even though Antarctic waters are dark for months at a time, the Southern Ocean supports abundant phytoplankton growth.

From Science Daily • Feb. 28, 2026

SAR11 populations often drop during the later stages of phytoplankton blooms, a period marked by rising levels of organic matter in the water.

From Science Daily • Feb. 2, 2026

She fed the zoae live phytoplankton and brine shrimp.

From Slate • Aug. 19, 2025

The creatures eat phytoplankton on the ocean surface which grow by transforming carbon dioxide into living matter through photosynthesis.

From BBC • Jul. 4, 2025

The phytoplankton, microscopic plants that float near the surface of water, had begun to remodel the lake into an environment that could once again sustain larger life.

From "Mountain of Fire" by Rebecca E. F. Barone