BAY ST. LOUIS, Miss. (AP) — Volunteers along U.S. coasts are raising oysters from tiny translucent spat to hard-shelled bivalves that can help restore depleted reefs. Oyster reefs are a keystone of coastal ecosystems. Each oyster filters 25 to 50 gallons of water a day. Spat glue themselves to larger oysters and grow. The reefs provide habitat for shrimp, crabs and many kinds of fish, and can also protect shorelines. Just in Maryland, Virginia, Mississippi and Alabama there are more than 1,000 oyster gardens. Most are in wire cages hanging from private docks or open-topped floats tied up like dinghies.