bathyal zoneとは 意味・読み方・使い方

The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is that part of the pelagic zone that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The average temperature hovers at about 39°F (4°C). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning there can be no primary production. It is known as the midnight zone because of this feature. Because of the lack of light, some species do not have eyes, however those possessing eyes in this zone include the viperfish and the frill shark. Many forms of nekton live in the bathyal zone, such as squid, large whales and octopuses, but this zone is difficult for fish to live in. Sponges, brachiopods, sea stars, and echinoids are also common in the bathyal zone. The fish in this zone have become very energy efficient, since it is especially hard to find nutrients. Many have slow metabolic rates to conserve energy. The fish here have weak muscles, soft skin and slimy bodies. Animals in the bathyal zone are not threatened by predators that can see them, so they do not have powerful muscles. Animals need to have the right adaptions to survive in this lethal area. There are few plants because of lack of sunlight, as they need sunlight to produce their food through photosynthesis. The bathyal zone holds some of the world's largest whales.