Deep sea ecology: seamounts

Bear Seamount with Physalia Seamount in the background, off the east coast of the US. Bear Seamount ... / ©: NOAA Ocean Explorer
Bear Seamount with Physalia Seamount in the background, off the east coast of the US. Bear Seamount rises 2000m from the ocean floor to a depth of 1100m.
© NOAA Ocean Explorer
Rising from the ocean floor to heights of 5,000m, seamounts are underwater mountains formed from volcanoes or sunken islands.
Some seamounts reach into surface, sunlit waters - or even break above the water to form islands - while others have their peaks a kilometre below the ocean surface.

Teeming with life
Unlike the continental slope and abyssal plain, deep-sea seamounts are densely inhabited. This is due to the currents of nutrient-rich water forced up their sides from the ocean floor. Cold-water corals, sponges, sea anemones, and sea fans form crowded communities on the rocky slopes, filtering these nutrients out of the water. Through this jungle move starfish, tiny lobsters, fish, and worms.

Like above-water islands, many seamounts have their own endemic species, which live nowhere else. A recent study of 24 seamounts near Tasmania, Australia, identified more than 850 species living on their slopes, most of which were unique to a particular seamount. Around one-third were new to science. Several of these are 'living fossils' - species from animal groups previously believed extinct since the time when dinosaurs roamed on dry land. With just a handful of the world’s estimated 31,000 seamounts having been explored, we can expect many more new species to be found.

Other species also visit seamounts. Normally scattered throughout the open ocean, many pelagic deep-sea fish species periodically gather in huge numbers at seamounts to feed and spawn. These include commercially valuable species such as orange roughy.

Find out about surface-water life on seamounts...

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