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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 .
1 Demersal zone, Spiny-back eel, Whitesaddled catshark, Speckled catshark, Whitenose whipray, Whitespotted grouper
Similarly, an organism living in a demersal habitat is said to be a demersal organism, as in demersal fish. Pelagic habitats are intrinsically ephemeral, depending on what ocean currents are doing. The land-based ecosystem depends on topsoil and fresh water, while the marine ecosystem depends on dissolved nutrients washed down from the land.
Demersal zone – the zone at or near the bottom of a sea or lake. Inhabitants of the demersal zone feed off the bottom or off other demersal fish. See also pelagic zone. Demersal fish – fish that live in the demersal zone. Examples are cod, flounder and snapper. Compared to pelagic fish, demersal fish contain little oil. See also bottom feeder.
The design requirements of a bottom trawl are relatively simple, a mechanism for keeping the mouth of the net open in horizontal and vertical dimensions, a "body" of net which guides fish inwards, and a "cod-end" of a suitable mesh size, where the fish are collected.
The word demersal comes from the Latin demergere, which means to sink. Demersal fish are bottom feeders. They can be contrasted with pelagic fish, which live and feed away from the bottom in the open water column. Demersal fish fillets contain little fish oil (one to four per cent), whereas pelagic fish can contain up to 30 per cent.
The Tonga–Kermadec subduction zone (also known as Kermadec–Tonga or Tonga–Kermadec-Hikurangi subduction zone) is a convergent plate boundary that stretches from the North Island of New Zealand northward. The formation of the Kermadec and Tonga plates started about 4–5 million years ago.
Ocean surfaces occupy 72% of the Earth's total surface. They can be divided into surfaces of the relatively shallow and nutrient rich coastal areas above the continental shelves (light blue), and surfaces of the more expansive and relatively deeper but nutrient poor ocean that lies beyond (deep blue).