Introduction

The North Atlantic is characterized by relatively wide continental shelves, particularly in its northerly portions, with steep slopes to the abyssal plain1. The width of the shelf decreases towards the south, with typical boundary current systems, characterized by strong seasonal upwelling, off the Iberian Peninsula and northwest Africa. Two chains of volcanic islands, the Azores and the Canaries, are located in the east central North Atlantic, and a large number of islands of volcanic origin, many with associated warm water coral reefs, are found in the southwest portion of the North Atlantic. In the far north of the region is the world's largest island, Greenland, primarily of Precambrian origin, whereas Iceland and the Faroe Islands are of more recent volcanic origin. All have rugged coastlines with rich faunas.

The biota of the North Atlantic is strongly influenced by both the warm Gulf Stream flowing north-eastward from the Gulf of Mexico and the Caribbean to northwest Europe, and the cold, fresh Labrador Current flowing south from the Canadian Archipelago and Greenland to the northeast coast of the United States. Major oceanographic and associated biotic regime shifts have been documented in the North Atlantic, but not with the frequency or scale of the North Pacific.

Around the coasts of the North Atlantic are a number of semi-enclosed seas. These seas have distinct oceanographic and bathymetric regimes, and ecosystems with many characteristics determined by local-scale processes and pressures. Hence each of these semi-enclosed seas, including the Black Sea, Mediterranean Sea, Baltic Sea (and similar coastal estuaries of the United States), the Caribbean Sea, and the Gulf of Mexico, receive some individual consideration in this assessment. Within the North Atlantic, there are several habitat types of special importance for biodiversity, such as seagrass beds and cold- and warm-water corals. Since these are important where they are found on the globe, they are treated in an integrated manner, respectively, in chapters 47, 42-43, rather than separately.

Coastal areas of the Northeast Atlantic have been settled in and used for several millennia. Commercial fisheries, both coastal and, as technology developed, offshore, have exploited fish and shellfish resources for centuries as well (Garcia et al., 2014), with periods of widespread overfishing in the twentieth century.