Question

Write a "write-up" or "thesis" on the topic : 'Importance of seamounts in oceans'.

The assignment/write-up/thesis should be two pages and should have references (total references not exceeding 10).   

This question/Assignment is from marine biology.

Answer 1

Seamounts are underwater mountains that rise from the seafloor. They are formed from extinct volcanoes that rise abruptly. The rise in the seafloor surface is reported to be from 1000-4000m in height. Most seamounts are volcanic in origin and are found on oceanic crust. Around 9,951 seamounts covering area of around 8,088,550 km2 (3,123,010 sq mi) have been mapped till now. Seamounts can be found in every ocean basin in the world but reported to be abundantly present in the North Pacific Ocean which accounts to around 4.39% of the ocean region. Till now 16 seamounts from Arctic Ocean, 23 seamounts from Mediterranean and Black seas have been reported. They possess an average area of 790 km2. The small seamounts have been found in Arctic Ocean and the Mediterranean and Black Seas, while largest mean seamount (size of about 890 km2) has been reported from Indian Ocean. The largest seamount with an area of 15,500 km2 occurs in the North Pacific. These include the Hawaiian (Emperor), Mariana, Gilbert, Tuomotu and Austral Seamounts. Active seamounts have been observed in Hawaiian Islands. Here the seamounts are found in groups or as submerged archipelagos. Example Emperor Seamounts.              

                   Seamounts were formed millions of years ago by volcanism and got subsided far below sea level. They are built in a dynamic oceanic setting resulting in horizontal subsidence as the seamount moves with the tectonic plate towards a subduction zone. Shallow-water seamounts are dominated by sedimentary rocks. Lava flows from mid-ocean ridge and plate boundary seamounts are basaltic, whereas lava flows from subducting ridge volcanoes are calc-alkaline. Seamounts formed from the subduction zone generally have more sodium, alkali and less magnesium. Ocean-ridge volcanoes show a pattern in eruptive activity. In the first stage, volcano erupts basalt of various types due to melting of mantle. In the second (active) stage, tholeiitic to mildly alkalic basalt erupt due to melting f mantle in the larger area. Seamounts of various structural shapes have been reported ranging from conical to flat-topped to complexly shaped.

               They are regarded as hotspots of marine biodiversity. They form home of many endemic species. They provide habitats and spawning grounds for larger animals including fishes. Some species, such as Allocyttus niger, Apogon nigrofasciatus occur more on seamounts than other parts of ocean floor. Marine mammals, sharks, tuna, and cephalopods also inhabit the seamounts as they get species of seabirds to feed. Seamounts support extensive fisheries. Soft sediments on seamounts are inhabited by polychaetes (annelid marine worms), oligochaetes (microdrile worms), and mollusks. They act as stopping points for migratory animals. Many species of fish and shellfish are commercially harvested from them. These include lobsters (Palinuridae), crabs (Paralithodes camtschaticus), tuna (Scombridae).

                Biodiversity of seamounts face threats due to extensive fishing and deep sea mining. Corals from seamounts are also vulnerable. Damage to seamounts and their overexploitation can lead to severe severely affect ocean health, food security, medicine and other services provided by oceans. Extensive fishing in the 20th century, poor management practices and increased pressure have lead to depletion of seamounts. Because of overfishing at their spawning grounds, species of orange roughly (Hoplostethus atlanticus) and the pelagic armorhead (Pseudopentaceros richardsoni) have gone down and this may take several years to the species to restore itself.

                There is an urgent need to ensure seamount conservation through measures such as marine protected areas. Many seamount species grow and reproduce slowly and are therefore highly vulnerable to unsustainable fishing and mineral exploration, through potential overexploitation and habitat destruction.

References

Nybakken, James W. and Bertness, Mark D., 2008. Marine Biology: An Ecological Approach. Sixth Edition. Benjamin Cummings, San Francisco

Seamount Scientists Offer New Comprehensive View of Deep-Sea Mountains. ScienceDaily. 23 February 2010.

McClain, Craig R.; Lundsten L., Ream M., Barry J., DeVogelaere A. (2009) Rands, Sean, ed. Endemicity, Biogeography, Composition, and Community Structure On a Northeast Pacific Seamount. PLoS ONE. 4 (1): e4141.

Lundsten, L; J. P. Barry, G. M. Cailliet, D. A. Clague, A. DeVogelaere, J. B. Geller (2009). "Benthic invertebrate communities on three seamounts off southern and central California". Marine Ecology Progress Series. Inter-Research Science Center. 374: 23–32..

Pual Wessel; David T. Sandwell; Seung-Sep Kim. The Global Seamount Census. Oceanography. Seamounts Special Issue. Oceanography Society. 23 (1). ISSN 1042-8275.

Morato, T., Varkey, D.A., Damaso, C., Machete, M., Santos, M., Prieto, R., Santos, R.S. and Pitcher, T.J. (2008). Evidence of a seamount effect on aggregating visitors. Marine Ecology Progress Series 357: 23–32.

Telmo Morato, Simon D. Hoyle, Valerie Allain, Simon J. Nicol Seamounts are hotspots of pelagic biodiversity in the open oceanProc Natl Acad Sci U S A. 2010 May 25; 107(21): 9707–9711.