<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>

How much of the earth is covered by marine biomes and how many types are there
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