What are phytoplankton?

Phytoplankton are primarily composed of single-celled or colonial algae that live in the water column of oceans, seas, and freshwater environments. These microscopic organisms are crucial to aquatic ecosystems as they perform photosynthesis, using sunlight to produce energy and oxygen, which supports a wide range of marine and freshwater life.

Phytoplankton serve as the foundational component of the aquatic food web, serving as primary producers that convert inorganic substances into organic matter. This process supports the growth of larger organisms, including zooplankton, fish, and larger marine animals. Their abundance and diversity can have a significant impact on water quality and the overall health of aquatic ecosystems, as they play a vital role in nutrient cycling and carbon fixation.

In contrast, the other options refer to different entities: multi-cellular plants represent a different level of aquatic life; terrestrial fungi are not related to water ecosystems; and substances used to enhance water clarity do not define phytoplankton but may have associations with water quality management.