Nearly all marine life relies on zooplankton in its diet, on some level or another. Zooplankton have a diet of their own and feed off the other members of the plankton family. Zooplankton are the largest of the plankton organisms and are naturally at the top of the plankton food chain. Zooplankton is an important part of the marine life cycle. Smaller organisms feed off zooplankton in the water column and in turn, larger organisms feed off these. This chain goes all the way up to the apex predators like: fish, birds, seals and whales.
The plankton family can be broken down into three main groups, with countless variations in each family. The three families create a cycle of existence among themselves and live off of each other and the many nutrients found in the water column. Each family plays an important part in the balance of marine life.
Bacterioplankton are the smallest member of the plankton family and consist of tiny bacteria like organisms that live off of mineral compounds and smaller, one-celled organisms. Bacterioplankton is similar to air-borne bacteria and makes up the base food group of the larger organisms and other plankton types.
Phytoplankton are the plant family of the plankton world and provide a food source to both the zooplankton's diet and larger organisms like krill. Phytoplankton uses the sun's light and nutrients in the water as food to grow. Phytoplankton operate much in the same way that land based plants do and convert light into usable energy. Phytoplankton are the main food source to zooplankton and as such are an important level of the plankton chain.
Zooplankton are the top "predator" in the plankton family and feed off both phytoplankton and bacterioplankton. Zooplankton are the animals of the plankton family and are more complex than bacterioplankton and phytoplankton. Zooplankton are an important level of the food chain and provide a food source to thousands of species both directly and indirectly. A zooplankton diet is common for many crustaceans and fish and provides an abundant food group in even harsh climates.
In many studies, it has been found that zooplankton are a direct food source for fish fry and only a few food chain links away from fish species that are common in a human diet. Zooplankton provide the perfect diet for small organisms that support the base of a food chain and are a crucial link in the life cycle of nearly all marine life.