The oceans of the Earth are full of life, from tiny plants to the biggest whale shark. The plants and animals in the ocean need each other to survive.
Plankton is the name for tiny animals and plants that float in the ocean. Each one is only about 1 millimetre long! Billions of these tiny little plants live in the oceans. They are the most important type of food for lots of fish and sea-birds. Without them, there would hardly be any life in the sea at all!