The transfer of energy from organism to organism forms a series called a food chain. All the possible feeding relationships that exist in a biome make up its food web. In the ocean, as elsewhere, the food web consists of producers, consumers, and decomposers. These types of organisms all transfer energy within the ocean environment.

Phytoplankton are the primary producers in the oceans. They produce organic materials from inorganic chemicals and outside sources of energy, primarily the Sun. Producers are sometimes called autotrophs, meaning "self-feeders." Green plants are an example of producers because they manufacture the compounds they need through photosynthesis.

Zooplankton and other animals are consumers. Zooplankton that eat only plants are primary consumers in the oceanic food web. Secondary consumers eat the plant-eaters and include zooplankton that eat other zooplankton. Tertiary consumers are the predators, such as tunas and sharks. Humans fall...