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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 ...
The distinction between demersal species of fish and pelagic species is not always clear cut. The Atlantic cod (Gadus morhua) is a typical demersal fish, but can also be found in the open water column, and the Atlantic herring (Clupea harengus) is predominantly a pelagic species but forms large aggregations near the seabed when it spawns on banks of gravel.
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.
Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.
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 very bottom, including the sediment surface and some subsurface layers. Marine organisms such as clams and crabs living in this zone are called benthos. Just above the benthic zone is the demersal zone.
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]
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.