<P> Coral reefs are one of the most well - known marine ecosystems within the world . The largest being that of the Great Barrier Reef . These reefs are composed of large coral colonies of a variety of species living together . The corals form multiple symbiotic relationships with the organisms around them . </P> <P> The deep sea conquers up to 95% of the space occupied by living organisms . Combined with the sea floor (or benthic zone), these two areas have yet to be fully explored and have their organisms documented making these ecosystems some of the hardest to understand by scientists . </P> <P> In addition to providing many benefits to the natural world, marine ecosystems also off an abundance of ecosystem services to humans as well . From fish sold in the market to carbon dioxide riddance provided by seagrass beds, there are multiple services provided that fall into one of four categories: supporting services, provisioning services, regulating services, and cultural services . </P>

Where are the most highly productive tropical marine ecosystems found