free-floating small protozoa, crustaceans (such as krill), etc. and the eggs and larvae from larger animals.
microscopic algae that float in the oceans, using the energy of sunlight to make food and grow, are called phytoplankton. together with zooplankton – tiny animals and animal-like organisms – they float near the water’s surface. in the right conditions, phytoplankton can multiply rapidly, turning water green or red. they are the ultimate source of food for almost all marine life. factmonster.com