We have published the first world scale map of marine biogeographic realms based on empirical data analysis of the distribution of 65,000 species (Costello et al. 2017). Realms are geographic areas with a high proportion of species that only occur within them (i.e. endemic species). They represent the biogeographic consequences of speciation and dispersal of species over evolutionary timescales.

The maps show the realms following analysis of species in 5-degree latitude longitude squares (top map) and then simplified and smoothed. The dotted grey line is the 1,000 m depth contour.

The boundaries of the 30 realms are coarse due to the limited spatial resolution of the available data. However, the general distribution of the realms agrees with the observations of naturalists and previous expert assessments.

In addition, the analysis showed that species which are pelagic are more widespread than benthic, and coastal than offshore. Thus endemicity is highest in benthic species and there are more coastal than offshore realms.

The most widespread species in the ocean were the smallest and largest; the microscopic plankton that drift until they find suitable conditions for growth, and the whales, birds, turtles, and large fish “megafauna” that travel across the oceans.


The map will have practical use for conservation planning (each realm should have a network of Marine Reserves), and reporting on ocean trends (by definition each realm is unique and so needs separate surveillance).



This work would not have been possible without the Census of Marine Life establishing its most enduring legacy, the Ocean Biogeographic Information System (OBIS) (Costello et al. 2007). OBIS contains over 45 million distribution records of over 100,000 species, integrated from thousands of datasets provided by over 500 organisations and 56 countries.


Costello MJ, Tsai P, Wong PS, Cheung A, Basher Z., Chaudhary C. 2017. Marine biogeographic realms and species endemicity. Nature Communications 8 (1057).

Data and GIS files at Figshare: https://doi.org/10.17608/k6.auckland.5086654.v1 and https://doi.org/10.17608/k6.auckland.5596840.v1

Costello MJ., Stocks K., Zhang Y., Grassle J.F., Fautin D.G. 2007. About the Ocean Biogeographic Information System. Retrieved from http://hdl.handle.net/2292/5236

Print Friendly, PDF & Email