Sea grass is a key part of continental shelf ecosystems where phytoplankton produce carbonate sediment. This kind of ecosystem occurs in subtropical places like Florida Bay, and around Bermuda. Sea grass beds often contain many species from various phyla. Apparently, seagrass herbivory is a highly important link in the food chain. Many species feed on sea grasses, such as green turtles, dugongs, manatees, fish, geese, swans, sea urchins and crabs.