Seagrasses, a group of about 60 species of underwater marine flowering plants, grow in the shallow marine and estuary environments of the world's continents except Antarctica. They are the primary food of animals such as manatees, dugongs and green sea turtles, and a critical habitat for thousands of other animal and plant species. Many seagrass habitats around the world have been completely destroyed or are in rapid decline. This is the first comprehensive global synthesis.