<P> Seagrasses are flowering plants from one of four plant families which grow in marine environments . They are called seagrasses because the leaves are long and narrow and are very often green, and because the plants often grow in large meadows which look like grassland . Since seagrasses photosynthesize and are submerged, they must grow submerged in the photic zone, where there is enough sunlight . For this reason, most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms . </P> <P> Seagrasses form extensive beds or meadows, which can be either monospecific (made up of one species) or multispecific (where more than one species co-exist). Seagrass beds make highly diverse and productive ecosystems . They are home to phyla such as juvenile and adult fish, epiphytic and free - living macroalgae and microalgae, mollusks, bristle worms, and nematodes . Few species were originally considered to feed directly on seagrass leaves (partly because of their low nutritional content), but scientific reviews and improved working methods have shown that seagrass herbivory is a highly important link in the food chain, with hundreds of species feeding on seagrasses worldwide, including green turtles, dugongs, manatees, fish, geese, swans, sea urchins and crabs . </P> <P> Seagrasses are ecosystem engineers in the sense that they partly create their own habitat . The leaves slow down water - currents increasing sedimentation, and the seagrass roots and rhizomes stabilize the seabed . Their importance to associated species is mainly due to provision of shelter (through their three - dimensional structure in the water column), and due to their extraordinarily high rate of primary production . As a result, seagrasses provide coastal zones with ecosystem services, such as fishing grounds, wave protection, oxygen production and protection against coastal erosion . Seagrass meadows account for 15% of the ocean's total carbon storage . </P> <P> Reefs comprise some of the densest and most diverse habitats in the world . The best - known types of reefs are tropical coral reefs which exist in most tropical waters; however, reefs can also exist in cold water . Reefs are built up by corals and other calcium - depositing animals, usually on top of a rocky outcrop on the ocean floor . Reefs can also grow on other surfaces, which has made it possible to create artificial reefs . Coral reefs also support a huge community of life, including the corals themselves, their symbiotic zooxanthellae, tropical fish and many other organisms . </P>

Why are sea turtles found in all areas of saltwater except for the arctic ocean (2 points)