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Ocean food webs and food chains

Life in the ocean depends on plants called phytoplankton that make food with energy from the sun.


Food is the energy that makes life possible for all animals.

  • Plants make food by taking energy from the sun. This is called photosynthesis. The word ‘photo’ means ‘light’ and ‘synthesis’ means ‘to make things’. 
  • Animals cannot make food but have to eat either plants or animals to get their energy. 

Food Chains

A food chain is a model of how energy moves from one organism to another in a community.

  • All food chains start with a plant. In the sea the most common plant is phytoplankton. Phytoplankton are tiny single celled plants too small to see with the naked eye. 
  • Animals that eat phytoplankton are called herbivores.
    • The most common ocean herbivore is zooplankton
    • Another ocean herbivore is krill. Krill is like a tiny shrimp about 5cm long. They eat mostly phytoplankton and sometimes zooplankton. Krill are a very important food for many larger animals such as fish, birds and whales.

Here are three Antarctic food chains:

Antarctic food web

Here is one food web combining the three food chains above:

Antarctic food web

Phytoplankton in the oceans use energy from the sun to make food. This is the start for all marine food chains. Image source


Ocean food webs start with tiny plants called phytoplankton. Image source


Tiny shrimp krill are an important food source for many marine mammals and fish. Image source

Next step learning: find out about other marine animals and build a marine food chain of your own (remember it must start with a plant!)