Inside the world of tiny phytoplankton – microscopic algae that provide most of our oxygen Shutterstock/Choksawatdikorn Friday, April 30, 2021 7:50 AM UTC Phytoplankton are microscopic algae living throughout the ocean’s surface waters. They can’t swim and are at the mercy of the currents and tides. Despite their small size, phytoplankton enable life in the oceans – and throughout the planet – to exist. There are two types of plankton – zooplankton, which are animals, and phytoplankton, which are algae. Phytoplankton are filled with chlorophyll which gives them a green colour, just like land plants. And like land plants, phytoplankton play a critical role, converting carbon dioxide and energy from the sun into food through photosynthesis, producing oxygen.