An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. An ecosystem can be as small as a pond or as large as a rainforest. Ecosystems are analysed and studied as unique entities. However, all ecosystems feature an energy input such as the sun's heat which keeps life in the system going. The oceans are the world's largest ecosystems and are considered to cover the shore as far as tidal waters come in.