Tiny plants that live near the surface of the ocean and are too small to see are phytoplankton. Many small sea creatures, like krill, feed on phytoplankton. Yum!
The word phytoplankton comes from Greek roots: phyton, "plant," and planktos, "wandering or drifting." Much plankton is composed of tiny animals, but the plankton made up of plants is phytoplankton. These microscopic organisms drift along close enough to the ocean's surface to photosynthesize, absorbing light and making their own food. Phytoplankton are an important part of the food chain — they're eaten by krill, which are eaten by baleen whales.