The once-plentiful eelgrass is the only type of seagrass now present in Boston Harbor; it is now confined to only four isolated areas, the largest of which is near the south coast of Bumpkin Island. Seagrass beds are critical wetlands components of shallow coastal ecosystems where they hold sediment, providing food and cover for a great variety of animals. Salt marshes, the most highly productive ecosystems in the world, are dominated by saltwater cordgrass and provide habitat for many marine organisms. More than 50 percent of the state's salt marshes have been filled. The largest remaining salt marshes on the islands are found on Thompson and Snake islands. Smaller brackish marshes have been identified on Calf, Grape, Lovells, and Peddocks. Mud flats, which generally occur on the periphery and at the expanding edges of