This data set shows North American marine ecoregions. Marine ecoregions are areas which fall within the Exclusive Economic Zones of the North American countries and which have general similarity in terms of physiographic, oceanographic, and biological characteristics. These marine ecoregions are constructed as a spatial framework with three nested levels. The data are intended to be scalable: appropriate for perspectives and interests varying from regional to continental in scope; ecosystem-oriented: based on a range of connected biological, oceanographic, and physiographic characteristics; and linked: related to other marine and terrestrial data sets, classification systems, and disciplines.

The 24 Level I marine ecoregions capture ecosystem differences at the most general scale by grouping together large water masses and currents, enclosed seas, and regions of coherent sea surface temperature or ice cover. The 86 Level II marine ecoregions capture the break between near-shore and oceanic areas, with the boundaries determined by large-scale features such as the continental shelf, continental slope, major trenches, and other features. Level II reflects the importance of depth as well as the importance of major physiographic features in determining current flows and upwelling. The 86 Level III marine ecoregions capture differences within the near-shore area and are based on local characteristics of the water mass, regional physiographic features, and biological community types. Level III ecoregions are defined only for the continental shelf, because this is the only ocean area for which sufficient information is available for finer-scale delineation.

The seaward boundaries of the marine ecoregions, as mapped, are approximate and do not represent the actual seaward boundaries of the ecoregions or an exact boundary of the Exclusive Economic Zones of the three countries.

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