World Ocean Census - Extract 18 - Seamount

24 May 2010

Seamounts are literally undersea mountains, which are usually defined as fully submerged mountains or hills rising 1,000 meters (3,300 feet) or more from the ocean floor. They are found throughout the world’s oceans, many in international waters, where they are governed by a complex array of multinational treaties.

Nearly half of them are in the Pacific Ocean, while the rest are found mostly in the Atlantic and Indian Oceans; overall, more are found in the Southern Hemisphere. Seamounts are often isolated, which contributes to the uniqueness and diversity of their ecosystems. Usually cone-shaped, they are often volcanic in origin – forming near mid-ocean spreading ridges, over upwelling plumes caused by rising seawater, and in island-arc convergent settings. Oceanic islands are seamounts that have breached sea level.

Census scientists estimate that fewer than 400 seamounts have been sampled, and of these, fewer than 100 have been sampled in any detail. A key aim of the Census is to increase the number of seamounts that have been explored and to ensure that they are sampled in sufficient detail to enable meaningful conclusions to be drawn about the life found there.

Seamounts can be hot spots of marine life in the vast expanses of the oceans, and the species found on them differ from those found on the surrounding deep ocean floor. Some seamounts have been shown to support high levels of biodiversity and unique biological communities. In some instances, high levels of endemic species (that is, those only found at that locality) have been found. Seamounts may act as regional centers of speciation (places where new species emerge), as stepping stones for dispersal across the oceans, and as places of refuge for species with a shrinking range. Census scientists have found that seamounts are home to an astonishing diversity of species, with 40 percent endemic to each mountain. Thousands of new species have been discovered in recent years – 600 on just five seamounts!

Text and images reprinted with permission from World Ocean Census: A Global Survey of Marine Life by Darlene Trew Crist, Gail Scowcroft and James M. Harding Jr., Firefly Books, 2009

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