The pelagial ( Greek πέλαγος pélagos , sea ') is the open water area above the bottom zone ( benthal ) in lakes and the sea . In the case of lakes, it extends from the middle of the lake to the shore to the first rooting aquatic plants . In the sea, pelagial refers to the free water body both near the coast above the continental shelf and on the open ocean.
The Pelagic Zones
In the sea, the pelagic is divided horizontally into a neritic province above the continental shelf including the coastal or tidal zone and into an oceanic province beyond the shelf edge. A slightly different terminology applies to sediments and sedimentary rocks , each of which is assumed to have a corresponding formation environment: shelf deposits are referred to as neritic sediments and oceanic deposits as pelagic sediments (see → Facial types of marine sedimentary rocks ). Vertically, the pelagial is divided into five depth zones according to the geomorphological subdivision of the water floor along the continental slope .
The Epipelagial (Gr. Επί epi "on") extends to a depth of 200 meters in the sea or, less often, in a lake and is characterized by positive bioproductivity and the highest biodiversity within the ecosystem . In addition to plankton , nectons also live here - particularly fish , marine mammals, crabs and cephalopods . The epipelagic zone is flooded by the sun and therefore allows multicellular algae , higher plants and photoautotrophic microorganisms to carry out photosynthesis . The area of the epipelagial in which this is possible depends on the properties of a body of water and is called the euphotic zone .
The mesopelagial (gr. Μέσον méson "middle") extends from 200 to 1000 meters depth and is the twilight zone of the sea between the light and dark deep zones, which is where its name comes from. Its lower limit marks the beginning of the actual deep sea , the aphotic zone . Although a little blue light still penetrates these depths, there is no photosynthesis and therefore no more vegetation; but now and then there is plankton . For example, the deep-sea hatchet fish live in the mesopelagic .
The bathypelagial (gr. Βαθύς bathýs "deep") ranges from 1000 to 4000 meters depth. The pressure in this deep zone is up to about 400 bar. There is no more sunlight, only some fish and bacteria produce light through bioluminescence . Animals living in this zone include squids , octopuses , starfish and large whales .
The Abyssopelagial (gr. Ἄβυσσος Abyss "bottomless") ranging from 4,000 to 6,000 meters deep. The animals that live here, including deep-sea angler fish , move at temperatures close to freezing and a pressure of up to 600 bar. Because food is sparse at these depths, some animals have mouths that are noticeably large so that they can prey on anything.
The Hadopelagial (Gr. Ἁΐδης , Hades , the underworld ) is the deepest zone and ranges from 6000 to about 11000 meters depth, the deepest point in the ocean. Here the pressure is up to 1100 times higher than on the water surface. As in the abyssopelagial, the temperature is close to freezing point. The bristle worms belong to the living things that occur here .
Eupelagial and Hemipelagial
As Eupelagial (gr. Ευ EU "well, well") or eupelagisch refers to the range of more than 2,400 meters deep. So it partially includes the aforementioned zones. The hemipelagial comprises the zone in front of the eupelagial in the range of 800 to 2400 meters. The terms are used in geology when looking at sediments (littoral, hemipelagic and eupelagic sediments, pelagic rain).
According to some marine biologists , bathypelagial, abyssopelagial and hadopelagial (also pelagic hadal , hadal pelagial, hadopelagic zone) can not be distinguished on the basis of their hydrological and biological characteristics. For this reason, they are often combined into one zone, the deep sea .
Production biological zones
- In a trophogenic zone ( nutrient layer , i.e. more oxygen and biomass is produced than consumed)
- In a tropholytic zone ( depletion layer , i.e. less oxygen and biomass is produced than consumed).
The boundary between the two zones is called the compensation level ( photosynthesis = respiration ⇒ biogenic net production = 0). It is located where the residual amount of light available for photosynthesis is so small that the oxygen and biomass generated by the plants ( producers ) in the light and dark reaction are completely consumed by them again through respiration. In the greater (i.e. tropholytic) water depths, the oxygen and all nutrients necessary for the organisms to live must therefore come from the trophogenic layer by means of substance transport, or the inhabitants ascend (vertical migration) and actively fetch the required substances. The actual position of the trophogenic layer and thus also the compensation level depends on the current photosynthetic output, which in turn is influenced by various factors. The light permeability of the water is determined by the local conditions (water turbidity, plankton density ), the photosynthesis output fluctuates in higher latitudes directly with the course of the seasons.
- The pelagial . At mare-mundi.eu, accessed on November 8, 2013.
- Jörg Ott: Oceanography - Introduction to the geography and biology of the oceans. Ulmer, Stuttgart 1988, ISBN 3-8001-2584-6 , pp. 131-132, p. 159
- Carol M. Lalli, Timothy R. Parsons: Biological Oceanography - an Introduction. 2nd Edition. Elsevier Butterworth-Heinemann, Oxford 1997, ISBN 0-7506-3384-0 , p. 3.