Many scientists believe that seamounts act like gigantic stirring rods in the ocean, where small-scale eddies break off from the large ocean currents. There are still many unanswered questions regarding the significance of seamounts. Seamounts with a height between 10 metres are marked in red, those higher than 3000 metres in blue. 3.14 > Seamounts are commonly located at volcanic structures such as the ocean ridges, and sometimes form long chains along the sea floor. This makes the seamounts especially interesting for fisheries. These include lower animals like sponges and sea cucumbers, relatives of the starfish, but also vertebrates such as fish, which can occur in large schools around seamounts with high species diversity. Research has shown that some seamounts are home to communities of unique, endemic species. The total number is estimated in the thousands. Today it is known that seamounts are present in all oceans. It was long believed that these were rare occurrences. Seamounts can be regarded as islands or volcanoes that do not reach up to the sea surface. Their peaks often rise up into the upper layers of the mesopelagic zone. Seamounts are underwater mountains that are formed by volcanic activity and rise at least 1000 metres above the sea floor. The species diversity in the deep sea was sensational for researchers. The great biological diversity discovered here was completely unexpected because the deep sea had long been considered to be a dead and muddy desert. In recent years researchers have been focussing on cold-water corals in particular, as well as the ecosystems around seamounts and at deep-sea hydrothermal vents and cold seeps. Most of them have only been superficially investigated and biologists are constantly discovering new species that have not yet been described. It is amazing that special biological communities have developed in the deep sea in spite of the darkness. There are also species that live near the bottom, but rise into the water column to hunt for food. Other species swim in the open water column and are called pelagic. Individual fish species have different modes of life. The kind of fish that predominate in an area depends in part on the bottom characteristics. Banks are composed of sandy material or massive rock. A bank is defined as a sea-floor elevation that can be several hundred kilometres long or wide. An example of this is the coast of Japan, where the sea floor descends abruptly and steeply into the depths.ĭistinctive structures rise from the sea floor all around the world: submarine banks, ridges and seamounts. Here the wide continental shelves and marginal seas are absent. There are also coasts, however, where the transition from the land to deep sea is more abrupt. The wide continental shelf ends at the break to the continental slope, which falls more steeply to greater depths. A similar situation is found off the coast of China with the South China Sea. The North Sea is situated here as a shallow, offshore marginal sea. Off the coast lies a sprawling continental shelf. Off northwest Europe the transition from land to the sea bottom is a gradual slope. The Food and Agriculture Organization of the United Nations (FAO) defines deep-sea fisheries as those conducted between the depths of 2 metres. Now fish are being caught from depths around 2000 metres, where the living conditions are fundamentally different from those in shallow regions. At first, fishing mostly targeted species of Sebastes, at depths of only a few hundred metres. At best, submersible vehicles provide only highlights in the vast darkness, and sea-floor samples obtained with grab samplers or trawls deployed from research ships allow only isolated snapshots of the deep-sea ecosystems.Īlthough the impact of human encroachment on these systems is largely unknown, the deep ocean regions have been fished since the end of the Second World War. So our knowledge of life at great depths is still fragmentary. Submersible robotic vehicles that can penetrate to the deepest parts of the ocean, the deep-sea trenches, have been in use for some time, but expeditions with these are expensive and complex. The deep sea refers to the totally dark layers of the ocean below around 800 metres. The assertion that the moon has been more thoroughly researched than the deep sea is still true.
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