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All organisms in the ocean are connected in a food chain
A food chain represents the transfer of body-building substances and energy when one organism eats another. Click on the image to show greater detail.

As far as we know, nearly all life in the ocean is dependent on plants. Only plants have the ability to manufacture food out of inorganic substances, such as energy from the sun. Thus all animals are dependent on plants, since animals cannot derive nutrition from inorganic substances. Plants produce; animals consume. Being producers, plants form the first link in the food chain.

A food chain is a sequence of organisms in which each is food for the next member in the sequence. The surface of the sea swarms with billions of microscopic plants, called diatoms. With other plants such as seaweed, diatoms form the first link in most marine food chains. All subsequent links in the food chain are consumers, or the animals.

Orcas (killer whales) often eat cod and cod eat bivalves, especially mussels and cockles. In turn, the bivalves feed on tiny zooplankton that they filter out of the water. These zooplankton eat even tinier plants: the diatoms and other phytoplankton. Thus the diatoms are the producers and the zooplankton, bivalves, cod and orca are all consumers.

In the ocean there are innumerable individual food chains overlapping and intersecting to form complex food webs. Most marine creatures eat a variety of foods. If one link in a chain is depleted, the other consumers in the chain have alternate food sources. Organisms generally belong to several different food chains that are linked to form a food web.

The rich diversity of life in the sea forms a delicately balanced network of predators and prey and all organisms are dependent on one another for survival.

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