<P> Marine ecosystems are among the largest of Earth's aquatic ecosystems . Examples include salt marshes, intertidal zones, estuaries, lagoons, mangroves, coral reefs, the deep sea, and the sea floor . They can be contrasted with freshwater ecosystems, which have a lower salt content . Marine waters cover two - thirds of the surface of the Earth . Such places are considered ecosystems because the plant life supports the animal life and vice versa . See food chains . </P> <P> Marine ecosystems are essential for the overall health of both marine and terrestrial environments . According to the World Resource Center, coastal habitats account for about one - third of marine biological productivity . Estuarine ecosystems, such as salt marshes, seagrass meadows and mangrove forests, are among the most productive ecosystems on the planet . Coral reefs provide food and shelter to the highest levels of marine diversity in the world . </P> <P> Marine ecosystems usually have a large biodiversity and are therefore thought to have a good resistance against invasive species . However, exceptions have been observed, and the mechanisms responsible in determining the success of an invasion are not yet clear . </P>

What is the most stable type of ecosystem