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The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. [1] The demersal zone is just above the benthic zone and forms a layer of the larger profundal zone .
Altogether, the pelagic zone occupies 1,330 million km 3 (320 million mi 3) with a mean depth of 3.68 km (2.29 mi) and maximum depth of 11 km (6.8 mi). [2] [3] [4] Pelagic life decreases as depth increases. The pelagic zone contrasts with the benthic and demersal zones at the bottom of the sea. The benthic zone is the ecological region at the ...
Demersal fish can be divided into two main types: strictly benthic fish which can rest on the sea floor, and benthopelagic fish which can float in the water column just above the sea floor. Benthopelagic fish have neutral buoyancy , so they can float at depth without much effort, while strictly benthic fish are denser, with negative buoyancy so ...
Demersal fish live on or near the sea floor, while pelagic fish live in the water column away the sea floor. Examples of such shallow water demersal fish, found in both tropical and temperate waters around the world, are seahorses, triplefins, wrasse and flounder. As demersal fish, all these fish spend most of their time on or near the sea floor.
Marine habitats can be broadly divided into pelagic and demersal habitats. Pelagic habitats are the habitats of the open water column, away from the bottom of the ocean. Demersal habitats are the habitats that are near or on the bottom of the ocean. An organism living in a pelagic habitat is said to be a pelagic organism, as in pelagic fish.
A school of large pelagic predator fish (bluefin trevally) sizing up a school of small pelagic prey fish . Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. [1]
Midwater trawling catches pelagic fish such as anchovies and mackerel, whereas bottom trawling targets both bottom-living fish and semi-pelagic species such as cod, squid, shrimp, and rockfish. Trawling is done by a trawler , which can be a small open boat with only 30 hp (22 kW) or a large factory trawler with 10,000 hp (7,500 kW).
Larval dispersal is one of the most important topics in marine ecology, today.Many marine invertebrates and many fishes have a bi-phasic life cycle with a pelagic larva or pelagic eggs that can be transported over long distances, and a demersal or benthic adult. [1]