What is plankton? Each drop of seawater is filled with life. This includes millions of tiny plants and animals that can only be seen with a microscope, including the eggs and larvae (babies) of fish and other marine animals. All of the tiny plants are called phytoplankton, while the animals are called zooplankton. Plankton makes up the base of the food web in the ocean – all life in the ocean depends on healthy plankton. Some of the zooplankton in the ocean comprises the eggs and larval stages o