The oceans cover 75% of the world's surface and contain 97% of its water; 90% of the seas lie beyond the shallow continental margins, and most are deeper than 2km.
With the advent of modern science we have been able to discover what some of the deep ocean is like, and also to exploit it - but there is still a vast area that remains unrecorded and explored.
action alert: If you like to eat fish, avoid deepsea species, and insist that your local supermarket or fish shop does not stock them on their shelves. See the MCS guide to alternative, environmentally responsible seafood choices,
www.fishonline.org
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deep sea factfile
- Life has reached even the deepest tracts of the ocean. Life at depth is dominated by animals, not plants, since light cannot penetrate here. Unusual, and to our eyes, bizarre animals have developed.
- Since no light penetrates this far, many animals have forsaken eyes and developed long feelers instead. Others have even developed systems for producing their own light - a process termed "bioluminescence". This light may be used as a lure to attract food; the deep sea angler fish is a good example with its glowing lures hanging down over its mouth to entice other fish to become its meal.
Since food is scarce to come by in the depths, some fish have developed stomachs with a huge capacity and can eat prey that are larger than themselves - the 'gulpers'.- Hydrothermal vents (also known as black smokers) occur where the Earth's crust is thin and new sea floor is being formed. Along these spreading ridges. mini volcanoes appear on the sea bed which belch out sulphur through chimneys up to 30m high into the surrounding ocean. They also cause a local increase in temperature by spewing out very hot water; temperatures of 350 degrees Celsius have been recorded from some of the sulphur chimneys.
- The areas around these vents are rich in life, particularly bacteria and dense populations of animals, because the food supply is so concentrated. The bacteria act as the primary producers of the vent food web. Many animals are very strange and completely new to science; some of the most spectacular are the giant red Pogonophoran tube worms, which can grow up to two metres long. Other gigantic forms of life include clams, which grow up to 30cms in length.
threats to deep ocean life
- Fisheries, mining, oil exploration and pipeline-laying threaten previously-undisturbed habitats, which are vulnerable to damage and over-exploitation.
- Many deepwater fish are very slow growing, and give birth to few young - they are very susceptible to overfishing, and some species are close to extinction after only a few years of fishing.
- Deep sea corals are slow-growing, and do not recover quickly from damaged caused by mechanised digging and mining, and by trawl nets.
