Phytoplankton
These microscopic, plant-like organisms drift in water, performing photosynthesis to fuel aquatic food webs and recycle nutrients.
Phytoplankton are microscopic, photosynthetic organisms that drift in aquatic environments, serving as the primary producers in marine and freshwater ecosystems. They include diverse groups like diatoms, dinoflagellates, and cyanobacteria, forming the base of the food web and driving global carbon cycles through photosynthesis.
What this means in real life
When a lake receives excess fertilizer runoff, phytoplankton populations explode, turning the water green and cloudy—a phenomenon called algal bloom that can deplete oxygen and harm fish.
What it isn’t
Not seaweed or visible aquatic plants. Phytoplankton are single-celled or simple colonial organisms invisible to the naked eye, whereas seaweed is a large, multicellular macroalga you can see and touch.
Commonly misused online
Often conflated with 'zooplankton' or lumped together as 'plankton' without distinction. Phytoplankton are the photosynthetic producers; zooplankton are the tiny animals that eat them—a crucial difference in food-web discussions.