Plankton are the floating or drifting plants and animals that live in marine, estuarine and fresh water. Most can only be seen under a microscope , yet they are remarkably abundant in the world s oceans. This means they also produce most of the oxygen breathed by humans and other animals.
Phytoplankton are also the basis of the marine food web .
They are grazed upon by small zooplankton who are in turn, eaten by small fish and other zooplankton. Since most plankton are barely visible to the unaided eye, scientists must use a special net to gather these small creatures. The net concentrates the plankton from hundreds of gallons of water that pass through it. A simple net can be constructed to capture microscopic plankton. The net is towed using a key ring and three strands of string which are tied onto a wire hoop.