All living organisms (plants and animals) must eat some type of food for survival. Plants
make their own food through a process called photosynthesis. Using the energy from the
sun, water and carbon dioxide from the atmosphere and nutrients, they chemically make
their own food. Since they make or produce their own food they are called producers.
Organisms which do not create their own food must eat either plants or animals. They are
called consumers. Some animals get their energy from eating plants while other animals
get energy indirectly from plants by eating other animals that already ate the plants.
Animals that eat only plants are called herbivores. Animals that eat both plants and other
animals are called omnivores. Animals that eat only other animals are called carnivores.
Some animals eat only dead or decaying materials and are called decomposers.
In the marine food web, special producers are found. They are tiny microscopic plants
called phytoplankton. Since the water is the home for these special tiny plants; it is also
the home for tiny microscopic animals called zooplankton. And of course, zooplankton
eat phytoplankton. Sometimes zooplankton and phytoplankton are collectively referred to
Food chains show the relationships between producers, consumers, and decomposers,
showing who eats whom with arrows. The arrows show the movement of energy through
the food chain. For example, in the food chain shown below, the small fish (silverside)
gets its energy by eating the plankton and the large fish (bluefish) gets its energy by
eating the small fish. Finally, the bacteria eats the fish after it dies, getting its energy from
the large fish. The bacteria also returns nutrients back to the environment for use by the
PHYTOPLANKTON ~~> ZOOPLANKTON ~~> SILVERSIDE ~~> BLUEFISH
NUTRIENTS <~~ BACTERIA
Thus the food chain becomes a complete circle. Animals may eat more than one type of
food. They may eat many different types of plants or many different animals. This makes
everything more complicated and the food chain becomes a food web.