Sea Mountain Life
There are mountains on land and there are mountains under the sea. The vast ocean seems flat but under that water are mountains, valleys and plains. These mountain chains rival the Alps, the Andes and the Himalayas in size and little is known about seamounts, the vast mountains hidden under the world's oceans. Now in a special issue of Marine Ecology scientists uncover the mystery of life on these submerged mountain ranges and reveal why these under studied ecosystems are under threat.
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface (sea level), and thus is not an island. These are typically formed from extinct volcanoes. They are defined by oceanographers as independent features that rise to at least 3,281 feet) above the seafloor. The peaks are often found hundreds to thousands of feet below the surface, and are therefore considered to be within the deep sea. There are an estimated 100,000 seamounts across the globe, with only a few having been studied. Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust near mid-ocean ridges, mantle plumes, and island arcs. Nearly half of the world's seamounts are found in the Pacific Ocean, and the rest are distributed mostly across the Atlantic and Indian oceans.
Because of their abundance, seamounts are one of the most common oceanic ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals, fish, and marine mammals alike.
The shape and size of our ocean depths are now resolved at a scale and detail unimaginable by early pioneers. Yet only about 300 have been well studied. This scarcity of knowledge provided the primary motivation for CenSeam, a seamount-focused field within the Census of Marine Life which commenced in 2005.
"The field of seamount ecology is rife with ecological paradigms, many of which have already become cemented in the scientific literature and in the minds of advocates for seamount protection," said Dr Ashley Rowden, one of the principal investigators of CenSeam. "Together, these paradigms have created a widely held view of seamounts as unique environments, hot spots of biodiversity with fragile ecosystems of exceptional ecological worth."
Researchers challenged the theory that seamounts act as hot spots of species richness, the weight of evidence now suggests that seamounts may have comparable levels of diversity to continental margins. However, it appears that their ecological communities are distinct in structure, and of higher biomass than neighboring continental margins.
Seamounts often project upwards into shallower water thus providing habitats for marine species that are not found on or around the surrounding deeper ocean bottom. Because seamounts are isolated from each other they form "undersea islands". As they are formed from volcanic rock, the substrate is much harder than the surrounding sedimentary deep sea floor. This causes a different type of fauna to exist than on the seafloor, and leads to a theoretically higher degree of endemic marine life. However, recent research especially centered at Davidson Seamount suggests that seamounts may not be especially endemic, and discussions are ongoing on the effect of seamounts on endemicity.
Much seamount research has been born out of the need to better manage these potentially vulnerable ecosystems. Globally, seamount ecosystems are under pressure from bottom-contact fishing and other human-related impacts.
Researchers detail the footprint of trawling and conduct a risk assessment that confirms what has long been suspected: seamount communities are highly vulnerable to disturbance by bottom trawling and recovery from fishing impacts is a lengthy process, likely requiring decades at a minimum.
For further information: http://www.eurekalert.org/pub_releases/2010-09/w-msu092010.php