The basic principles are applicable to the tropical reefs .
Big fish eat little fish.
This is a grossly simplified view of the undersea jungle. An understanding of the dynamics of the marine food chain provides some guide to keeping the fish and invertebrates alive in the aquarium. In this generalised diagram of the organic cycle of the sea, we can see that the presence of one group of creatures provides sustenance for more complex animals. Real seawater contains phytoplankton, invisible microalgae, single-celled organisms, principally diatoms and flagellates. Zooplankton is a vital part of the fry and juvenile fish of all species, and the adults of Pipefish and the Sea Horses .