Is plankton single celled

Plankton can be both single-celled and multicellular organisms. Phytoplankton, which are photosynthetic, are primarily single-celled algae, while zooplankton can include both single-celled organisms like protozoa and multicellular organisms like small crustaceans. Together, they form a crucial part of aquatic ecosystems, serving as a foundational food source for many marine species.