There are fertile coastal marshes in the National Seashore. Boardwalk I faces the sound on Big Lagoon. The waters of the sound are less salty than the waters of the Gulf. Nutrients washed down from the mailand give rise to a wealth of marine life. Here shrimp and fish valuable to commercial fishing pass portions of their lives, and creatures such as herons, egrets, alligators, and fiddler crabs reproduce and flourish. Without the protection afforded by the barrier islands, the plant and animal communities of the mainland coasts would not be as rich.