Reuters: The lowly oyster, a tasty delicacy to seafood lovers but a curiosity to more squeamish diners, is also the backbone of marine life along the U.S. Gulf Coast and among the most vulnerable creatures now threatened by a giant oil spill. The region’s oyster beds are the vital foundation of a commercial and recreational fishing industry — including shrimp, crabs and other shellfish — that generates $6.5 billion in annual revenues, according to one recent estimate. The networks of …