As demands on oceans grow, it is important to ensure that their resources are being conserved and carefully managed worldwide. A new study led by The Nature Conservancy and the World Wildlife Fund (WWF) — Marine Ecoregions of the World  — takes an important step toward that goal by presenting the first-ever classification system of the world’s coastal waters.

The report classifies the vast array of habitats and species in the world’s oceans by dividing costal waters into 12 realms (such as the Tropical Atlantic Ocean); 62 provinces (places like the Mediterranean Sea); and 232 ecoregions (smaller and more homogenous units such as the Northern Gulf of Mexico or the Marshall Islands). This new set of classifications will help conservation scientists recognize gaps in protection and set priorities for action, such as establishing marine protected areas. More than 12 percent of terrestrial areas are protected compared to less than one percent of marine habitats.

Click on the maps below to view the world’s marine ecoregions, provinces and realms (for the ecoregion map, please click each number to view ecoregion details):

, or ecological regions, capture areas of relatively homogenous species composition, often dominated by a smaller number of habitats, making them distinct from adjacent ecoregions. These are the finest scale units within the MEOW and represent a realistic "jumping-off point" for practical on-the-ground conservation.


 

Ecoregions

Provinces are distinctive sub-units of realms often centered on seas or semi-enclosed basins, typically with highly distinctive biotas and endemic species, but still containing a very broad array of habitats

Realms capture the highest levels of biological diversity - wide tracts of coasts and shelves with broad similarities, including unique taxa at generic and family levels. They reflect a shared evolutionary history driven by factors of temperature/latitude and isolation from other equivalent regions.

 

More complete definitions are provided in the full publication.

A Global Classification

Biological diversity varies over geographic space and the field of biogeography describes the form and pattern of this variation. Quite apart from its ecological and evolutionary interest, such biogeographical study has a critical role to play in nature conservation. Efforts to protect the planet's biodiversity require an understanding of how and where species are distributed. By ensuring a good representation of biogeographic units within a system of protected areas we can come close to ensuring that the full spectrum of life on Earth will also be protected.

Biogeographic maps thus lie at the heart of protected areas network planning and coverage assessment, and have been used as a basis for national and regional studies for a number of years. Simple biogeographic analyses have also been undertaken at the global level to assess progress and highlight gaps in the growing coverage of terrestrial protected areas. (The United Nations List of Protected Areas has regularly published such assessments back to 1980 (Chape et al. 2003).

The marine environment has lagged considerably behind the terrestrial in using such biogeographic tools: since the late 1990s a growing number of national and regional scale classifications have been devised for marine conservation planning, but the lack of a comprehensive global classification remained widely acknowledged. Although broad-scale systems do exist, none provide both a full global coverage and the fine scale spatial subdivisions necessary to drive representative area-based conservation planning.

Recognizing both the global need and the existence of a large number of incomplete global and regional systems two international nature conservation organizations — The Nature Conservancy and WWF — invited a number of other organizations to work with them in reviewing the existing classifications and to develop a synthesized product, a system of Marine Ecoregions of the World (MEOW). This is not a new biogeography, but rather a mosaic of existing, recognized spatial units.

The work was conducted by a small working group. An early draft was circulated as an information document to all member states of the Convention on Biological Diversity, while the final version was published in BioScience in July/August 2007.

Nature picture credits (top to bottom, left to right): Photo © Jez O'Hare (Palau, West Caroline Islands ecoregion); Photo © Mark Spalding/TNC (juvenile hawksbill turtle, Greater Antilles ecoregion).