Deep Sea Communities Information
Because of the high pressure, low temperature and absence of light, prior to the nineteenth Century scientists assumed life was sparse in the deep ocean. In the 1870s Sir Charles Thompson and colleagues aboard the Challenger expedition discovered many deep-sea creatures of widely varying types. This discovery raised another question: how can these creatures obtain food to feed themselves? In answering that question scientists have found three food sources supporting deep-sea creatures: marine snow, big organism falls, and chemosynthesis at hydrothermal vents.
giant tube worm-from NOAA
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History
The first discovery of any deep-sea chemosynthetic community including higher animals was unexpectedly made at hydrothermal vents in the eastern Pacific Ocean during geological explorations (Corliss et al., 1979).[1] Two scientists, J. Corliss and J. van Andel, first witnessed dense chemosynthetic clam beds from the submersible DSV Alvin on February 17, 1977, after their unanticipated discovery using a remote camera sled two days before.[1]
Deep sea
Mariana Trench-by KmusserThe deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline, at a depth of 1000 fathoms (1800 m) or more.
The deepest part of the deep sea is Mariana Trench located in the western North Pacific. It is also the deepest point of the earth's crust. It has a maximum depth of about 10.9 km which is deeper than the height of Mount Everest.[2]
In 1960, Don Walsh and Jacques Piccard reached the bottom of Mariana Trench in the Trieste bathyscaphe. The pressure is about 11,318 metric tons-force per square meter (110.99 MPa or 16100 psi).
Three main food sources
Marine snow
The upper photic zone of the ocean is filled with particle organic matter (POM) and is quite productive, especially in the coastal areas and the upwelling areas. However, most POM is small and light. It may take hundreds, or even thousands of years for these particles to settle through the water column into the deep ocean. This time delay is long enough for the particles to be remineralized and taken up by organisms in the food webs.
Scientists at Woods Hole Oceanographic Institution conducted an experiment three decades ago in deep Sargasso Sea looking at the rate of sinking.[3] They found what became known as marine snow in which the POM are repackaged into much larger particles which sink at much greater speed, 'falling like snow'.
Bottom plains
Because of the sparsity of food, the organisms living on and in the bottom are generally opportunistic. They have special adaptations for this extreme environment: rapid growth, effect larval dispersal mechanism and the ability to use a ‘transient’ food resource.
One typical example is wood-boring bivalves, which bore into wood and other plant remains and are fed on the organic matter from the remains.
Whale falls
Main article: whale fallFor the deep-sea creatures, a dead whale is the most exciting event. A dead whale can bring hundreds of tons of organic matter to the bottom.
Whale-fall community progresses through three stages:[4]
- Mobile scavenger stage: Big and mobile deep-sea animals arrive at the site almost immediately after whales fall on the bottom. Amphipods, crabs, sleeper sharks and hagfish are all scavengers.
- Opportunistic stage: One interesting genus is Osedax.[5] Osedax is an interesting tubeworm. The larva is born without sex. The surrounding environment determines the sex of the larva. When a larva settles on a whale bone, it turns into a female; when a larva settles on or in a female, it turns into a dwarf male. One female Osedax can carry more than 200 of these male individuals in its oviduct.
- Sulfophilic stage: Further decomposition of bones and seawater sulfate reduction happen at this stage. Bacteria create a sulphide-rich environment analogous to hydrothermal vents. Polynoids, bivalves, gastropods and other sulphur-loving creatures move in.
Hydrothermal vents
hydrothermal vent-by P. Rona Main article: hydrothermal ventHydrothermal vents, also called black smokers, were discovered in 1977 by scientists from Scripps Institution of Oceanography. So far, the discovered hydrothermal vents are all located at the boundaries of plates: East Pacific, California, Mid-Atlantic ridge, China and Japan.
New ocean basin material is being made in regions such as the Mid-Atlantic ridge as tectonic plates pull away from each other. The rate of spreading of plates is 1–5 cm/yr. Cold sea water circulates down through cracks between two plates and heats up as it passes through hot rock. Minerals and sulfides are dissolved into the water during the interaction with rock. Eventually the hot solutions emanate from an active sub-seafloor rift creating a black smoker.
Chemosynthesis of bacteria provide the energy and organic matter for the whole food web in vent ecosystems. Giant tubeworms can grow to 2.4 m (7 ft 10 in)[6] tall because of the richness of nutrients. By now, over 300 new species have been discovered at hydrothermal vents.[7]
Hydrothermal vents are entire ecosystems totally separated from the world of light. And they may be the first evidence that the earth can support life without the sun.
Cold seeps
Main article: cold seepA cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool.
References
This article incorporates a public domain work of the United States Government from the reference[1]
Notes
- ^ a b c Minerals Management Service Gulf of Mexico OCS Region (November 2006). "Gulf of Mexico OCS Oil and Gas Lease Sales: 2007-2012. Western Planning Area Sales 204, 207, 210, 215, and 218. Central Planning Area Sales 205, 206, 208, 213, 216, and 222. Draft Environmental Impact Statement. Volume I: Chapters 1-8 and Appendices". U.S. Department of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans. page 3-27. PDF
- ^ "deep sea". http://en.wikipedia.org/wiki/Deep_sea.
- ^ "Marine Snow and Fecal Pellets". http://www.whoi.edu/oceanus/viewArticle.do?id=2387&archives=true.
- ^ Shana Goffredi, Unusual benthic fauna associated with a whale fall in Monterey Canyon, California, Deep-sea Research, 1295-1304, 2004
- ^ Noah K. Whiteman, Between a whale bone and the deep blue sea: the provenance of dwarf males in whale bone-eating tubeworms, Molecular Ecology, 4395–4397, 2008
- ^ "Giant tube worm". http://en.wikipedia.org/wiki/Riftia.
- ^ Botos, Sonia. "Life on a hydrothermal vent". http://www.botos.com/marine/vents01.html#body_4.
Categories: Oceanography
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