Seamount

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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 volcanos, that rise abruptly and are usually found rising from a seafloor of 1,000 4,000 metres depth. They are defined by oceanographers as independent features that rise to at least 1,000 metres above the seafloor. The peaks are often found hundreds to thousands of metres below the surface, and are therefore considered to be within the deep sea.^[1] An estimated 30,000 seamounts occur across the globe, with only a few having been studied.

1 Geography
2 Ecology
3 Fishing
4 See also
5 References
6 Notes
7 External links

[edit] Geography

The locations of the world's major seamounts

Seamounts are often found in groupings or submerged archipelagos, a classic example being the Emperor Seamounts, which are an extension of the Hawaiian Islands, which were formed millions of years ago by volcanism, and have since subsided to below sea level. The long chain of islands and seamounts, extending thousands of kilometres northwest from the Big Island demonstrates the movement of a plate over a volcanic hotspot.

Isolated seamounts and those without clear volcanic origins appear to be less common. In recent years, geologists have confirmed that a number of seamounts are active undersea volcanoes: Lo‘ihi in the Hawaiian Islands and Vailu‘ulu‘u in the Manu‘a Group (Samoa) are examples.

[edit] Ecology

Seamounts often project upwards into shallower zones more hospitable to sea life, 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" creating the same biogeographical interest. 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 higher degree of endemism.

In addition to simply providing physical presence in this zone, the seamount itself may deflect deep currents and create upwelling. This process can bring nutrients into the photosynthetic zone, producing an area of activity in an otherwise desert-like open ocean. Seamounts may thus be vital stopping points for some migratory animals such as whales. Some recent research indicates whales may use such features as navigational aids throughout their migration. Due to the larger populations of fish in these areas overexpoitation by the fishing industry has caused some seamount fauna populations to decrease considerably.

The primary productivity of the epipelagic waters above the submerged peak can often be enhanced by the hydrographic conditions of the seamount.^[2] This increases the densities of the zooplankton and leads to the high concentrations of fish in these areas. Another theory for this is that the fish are sustained on the diurnal migration of zooplankton being interupted by the prescence of the seamount, and causing the zooplankton to stay in the area. It is also possible that the high densities of fishes has more to do with the fish life histories and interaction with the benthic fauna of the seamount.^[3] The benthic fauna of the seamounts is dominated by suspension feeders, including sponges and true corals. For some seamounts that peaks at 200-300 metres below the surface benthic macroalgae is common. The sedimentary infauna is dominated by polychaete worms

[edit] Fishing

The main cause for the recent interest in seamounts is the discovery that they maintain large stocks of commercially important fishes and invertebrates. This began during the 1960s when Russia, Australia and New Zealand started to look for new stocks of fish and began to trawl the seamounts. The majority of the invertebrates brought up are corals, and are mainly used for the jewelry trade. The two major fish species were the orange roughy (Hoplostethus atlanticus) and pelagic armourhead (Pseudopentaceros wheeleri), which were quickly overexploited due to lack of knowledge of the longevity of the fish, late maturity, low fecundity, small geographic range and recuitment to the fishery. As well as the fishes being overexploited the benthic communities were destroyed by the trawling gear.

[edit] See also

[edit] References

^ Nybakken, James W. and Bertness, Mark D., 2005. Marine Biology: An Ecological Approach. Sixth Edition. Benjamin Cummings, San Francisco
^ Boehlert, G. W. and Genin, A. 1987. A review of the effects of seamounts on biological processes. 319-334. Seamount, islands and atolls. Geophysical Monograph 43, edited by B. H. Keating, P. Fryer, R. Batiza, and G. W. Boehlert.
^ Rogers, A. D. 1994. The biology of seamounts. Advances in Marine Biology 30:305-350

[edit] Notes

Keating, B.H., Fryer, P., Batiza, R., Boehlert, G.W. (Eds.), 1987: Seamounts, islands and atolls. Geophys. Monogr. 43:319-334.
Koslow, J.A. (1997). Seamounts and the ecology of deep-sea fisheries. Am. Sci. 85:168-176.
Menard, H.W. (1964). Marine Geology of the Pacific. International Series in the Earth Sciences. McGraw-Hill, New York, 271 pp.