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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Benthic zone | 1/5 | https://en.wikipedia.org/wiki/Benthic_zone | reference | science, encyclopedia | 2026-05-05T07:34:28.462475+00:00 | kb-cron |
The benthic zone, from Ancient Greek βένθος (bénthos) 'the depths of the ocean', is the ecological region at the lowest level of a body of water, such as a stream, river, lake, or ocean, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos, or more informally bottom dwellers. They include microorganisms such as bacteria and fungi, as well as larger invertebrates such as crustaceans and polychaetes. Benthos generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.
== Physical description ==
=== Oceans === The benthic region of the ocean begins at the shore line (intertidal or littoral zone) and extends downward along the surface of the continental shelf out to sea. Thus, the region incorporates a great variety of physical conditions differing in depth, light penetration and pressure. The benthic zone includes all areas of bottom that are below the water. The continental shelf is a benthic region of a tectonic plate that extends away from the shoreline of a land mass. At the continental shelf edge, usually about 200 metres (660 ft) deep, the gradient greatly increases and is known as the continental slope. The continental slope drops down to the deep sea floor. The generally flat part of the deep-sea floor is called the abyssal plain and is usually about 4,000 metres (13,000 ft) deep. The ocean floor is not all flat but has submarine ridges, seamounts and deep ocean trenches known as the hadal zone. For comparison, the pelagic zone is the ecological region above the benthos, comprising the water column up to the surface. The benthos of the deep ocean includes the bottom levels of the oceanic abyssal zone. The deeper areas of the oceans beyond the penetration of daylight are the aphotic zone. Generally, this region is inhabited by life forms that tolerate cool temperatures and low oxygen levels, depending on the depth of the water.
=== Lakes === As with oceans, the benthic zone is the floor of the lake, which may be covered by accumulated sunken organic matter and mineral sediments, and the organisms that live in and on it. The littoral zone is the zone bordering the shore; light penetrates easily and aquatic plants thrive. The pelagic zone is the water between the surface and the bottom. the photic zone is the water column down to the depth to which no light penetrates. This depth varies depending on clarity of the water.
== Benthos ==