While the true Everglades is a freshwater habitat, its waters drain into and nourish the prolific estuarine and marine portions of Everglades National Park, the boundaries of which extend far out into Florida Bay and the Gulf of Mexico. Marine and estuarine fishes in these waters command abundant interest from aquarists, connoisseurs, and fishermen, but they are also an important food supply for many fish-eating birds.

The important ecological functions of the area are its support of fish-eating birds and its habitat as a nursery for a great many marine fishes, all based on the high productivity that arises from freshwater inputs from the Everglades as well as the neighboring Big Cypress Swamp ecosystems. Wading birds utilize the mud flats of Florida Bay, the shallows of the mangrove swamps, and other coastal habitats, and ospreys fish in the more open waters. All of these species prey heavily on the young of larger game fishes and on the high diversity of nongame species.

A vast number of marine and estuarine fishes occur in southern Florida. If only nearshore waters are included, the number is well over 500 — which is far greater than any other vertebrate group of southern Florida.

The marine and estuarine habitats of South Florida are highly diverse, including:

• Deep, open-ocean waters of the Florida Current in the Straits of Florida
• Coral reefs along the Florida Keys
• Continental shelf waters, which are narrow on the east coast but very broad in the Gulf of Mexico
• Estuaries and mangrove swamps
• Shallow-water grass flats of bays and coastal waters
• Protected, shallow, coastal embayments prone to dry-season hypersalinity