There could be up to 5 million species inhabiting the dark recesses of the sea, in ecosystems that are being destroyed even before they have been discovered. This rich and varied landscape has, until recently, been largely unstudied. Only since the development of submersibles able to withstand immense pressure have some of the secrets of the ocean depths been revealed.
Plankton and the carcasses of larger animals, drawn from the surface by gravity and currents, provide one source of energy in these completely dark waters, and cold-water coral on the seabed survives at depths of over 19,000 feet (6,000 meters), using tree-like branching structures to capture its food. Volcanoes thrust from the thin crust under the oceans, forming “seamounts”, and hydrothermal vents in the ocean floor belch out hydrogen sulphide, which microbes harness through chemosynthesis to provide another source of energy.
It is around seamounts that the most abundant deep-sea life is found. But even as these features are being identified and studied, they are being targeted by deep-sea bottom trawlers, which drag nets across the sea-bed, completely destroying any coral in its path. Such fishing practices contribute only around 1 percent of the world’s fish production but are wreaking immeasurable environmental damage.
Deep-sea species tend to be long-lived and slow to reproduce, and deep-sea trawling is causing their stocks to decline. Since trawling for orange roughy started in the late 1970s, stocks of this species are thought to have fallen by more than 70 percent in more than half the areas studied. In addition to the fish targeted by the trawlers, the nets bring up many other species, such as rare deep-sea sharks. The UN General Assembly called, in 2006, for urgent action to protect the fragile ecosystems on which these species depend. A meeting of 40 countries, organized by the UN Food and Agriculture Organization early in 2008, failed to draw up guidelines.
Localized damage to, and pollution of, the seabed is caused by drilling for oil and gas. As fields in shallower waters are nearing depletion, and technology is developed to drill at ever-greater ocean depths, companies are prospecting in deeper waters. Another potential source of energy, lying on the seabed itself, are nodules of frozen methane, although the technology for capturing the gas from these methane hydrates is still in its infancy. Interest has also been shown in sources of metals and minerals to be found at great depths on the ocean floor, with escalating prices for raw materials making the mining of these a more viable commercial proposition.
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