Marine ecoregions (ecological regions) are areas of the sea identified and defined based on biogeographic characteristics. A more complete definition describes them as “Areas of relatively homogeneous species composition, clearly distinct from adjacent systems” dominated by “a small number of ecosystems and/or a distinct suite of oceanographic or topographic features”. Ecologically they “are strongly cohesive units, sufficiently large to encompass ecological or life history processes for most sedentary species.”[1] A global classification of Marine Ecoregions of the World (MEOW)[1] was devised by an international team, including major conservation organizations, academic institutions and intergovernmental organizations. The digital ecoregions layer is available for download as an ArcGIS Shapefile.
This system has a strong biogeographic basis, but was designed to aid in conservation activities for marine ecosystems. The Marine Ecoregions of the World classification defines 232 marine ecoregions (e.g. Adriatic Sea, Cortezian, Ningaloo, Ross Sea) for the coastal and shelf waters of the world. These form part of a nested system and are grouped into 62 provinces (e.g. the South China Sea, Mediterranean Sea, Central Indian Ocean Islands) that, in turn, are grouped into 12 major realms. The latter are considered analogous to the eight terrestrial ecozones, represent large regions of the ocean basins: Arctic, Temperate Northern Atlantic, Temperate Northern Pacific, Tropical Atlantic, Western Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Tropical Eastern Pacific, Temperate South America, Temperate Southern Africa, Temperate Australasia, Southern Ocean.
Other classifications of marine ecoregions or equivalent areas have been widely developed at national and regional levels, as well as a small number of global schemes. One of the most comprehensive early classifications was the system of 53 coastal provinces developed by Briggs in 1974[2]. The near-global system of 64 large marine ecosystems has a partial biogeographic basis, while the World Wildlife Fund identified 43 priority marine ecoregions as part of it’s Global 200 efforts[3]. Each of these systems, along with numerous regional biogeographic classifications, was used to inform the MEOW system. The WWF Global 200 work also identifies a number of major habitat types that correspond to the terrestrial biomes: polar, temperate shelves and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic (trades and westerlies), abyssal, and hadal (ocean trench).