It's not exactly field guide-sized, but IS "an illustrated guide to fishes, invertebrates, and plants of bays and inlets from Cape Cod to Cape Hatteras." It also discusses the natural history of the organisms. Yay!
This book used to be subtitled "Invertebrates and Seaweeds of the Atlantic Coast from the Bay of Fundy to Cape Hatteras." It helped me identify comb jellies and a few other weird beasties near Chesapeake Bay.