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Early explorers classified the land into “biogeographic” realms based on their distinctive fauna and flora. On land the contrast was obvious – kiwi in New Zealand and kangaroos in Australia, for example – but the ocean realm was different. Experts doubted whether distinct biogeographic boundaries existed in the oceans, partly because for species like whales, birds, and large fish, the whole ocean is their habitat. Before OBIS existed it was too difficult and expensive to collate the tens of thousands of species distribution records from many thousands of publications, specimen collections’, and unpublished sources to test this. Now, using cluster analysis of species distributions in OBIS, 30 distinct realms have been identified, of which two are largely freshwater (Baltic and Black Seas).Two-thirds of all realms were coastal, because the coastal environment is less stable and more variable. Because the offshore and deep-sea areas offer similar environmental conditions over much larger areas the species there have larger geographic ranges; thus offshore realms are larger than coastal. 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. In addition to improved understanding of ocean biogeography, these new maps 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).
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