The Grand Banks are among the most biologically productive marine areas in the world. The confluence of the Labrador Current and the Gulf Stream, and the tidal mixing of the water column on the shallows of the continental shelf, provide ideal feeding and spawning conditions for thousands of species.

Benthic, or bottom-dwelling, communities are rich with invertebrates, such as barnacles, sea stars, crabs, lobster, sponges, scallops, clams and jellyfish, to name a few. Common fish populations historically included Northern Cod, Redfish, Herring, Silver Hake, and the now-famous Greenland Halibut, or turbot. The Northern Cod spends part of its life-cycle migrating between the Atlantic and the Northwest Atlantic marine ecozones. Thanks to chronic overfishing by Canada and other nations, commercial harvests of many of these species are no longer sustainable, and there are fears the once-rich Grand Banks cod may never again support a commercial fishery.

Common marine mammals in this ecozone include Harbour and Grey Seals, Harbour Porpoises, and dolphins. Several species of whale are indigenous to or migrate through the ecozone, including the Northern Bottlenose, Blue, Pilot, Beluga, Fin, Minke, and Humpback Whale.

Significant proportions of the North American or world populations of seabirds live within the ecozone. Large numbers overwinter on the open ocean off Newfoundland and Nova Scotia, only coming ashore to find mates. Among them are the Northern Fulmar, Greater Shearwater, Dovekie, and Common and Thick-billed Murres. Breeding colonies for Leach's Storm Petrel, Kittiwakes, Puffins, and Common Murres can be found on Newfoundland's Baccalieu Island and Witless Bay Islands. Cape St. Mary's hosts Gannets, Kittiwakes and Common Murres. Machias Seal Island in the Bay of Fundy supports large colonies of Puffins and Arctic Terns. And there are large populations of Shearwaters, Eiders and Cormorants, and gulls throughout the region.

The low-lying beaches, salt marshes and tidal flats of the Upper Bay of Fundy and the southern Gulf of St. Lawrence are dominated by burrowing crustaceans, such as Corophium and Annelid worms. These are extremely abundant at or just below the surface of the mudflats, and are fed upon by migratory birds and other shorebirds. This habitat is the product of the huge tidal fluctuations in the Upper Bay of Fundy, which top 15 metres.

Estuaries, where fresh river waters mix with saline sea water, are productive habitats. They serve as nursery areas for juvenile fish and the planktonic larvae of mollusks, crustaceans, and other invertebrates. The estuaries of the Gulf of Maine are thought to be vital to almost three-quarters of the commercially-significant fish species in the area.