Why does plankton live in shallow water


plankton, The entirety of the organisms floating in the free water (pelagic) with little or no movement of their own. In contrast to the Nekton, the P. cannot overcome the currents of water. The condition for life in free water is that the sink rate is reduced to a minimum. In the case of forms that are actively movable, the sinking can be compensated to a certain extent by their own movement. The sinking is also counteracted by turbulence in the water and by the deposition of light substances (fats, oils, gases) in the density of the organisms. In addition, the relative surface area of ​​the organisms also plays a role in the ability to float. This can be increased, among other things, by the formation of body processes that are common in radiolarians and crabs, for example. Despite all devices to reduce the sink rate, the majority of the P. can only float with the support of the turbulence in the water.

The horizontal distribution of the P. is almost homogeneous, its depth distribution, however, according to the changing living conditions with increasing depth, very heterogeneous. Vertical ones are formed P. stratificationsdepending on the time of day and time of year. Main proximate cause of the Vertical hikes the zooplankton is the change in light intensity over the course of a day. During the day, many phytoplankton migrate to areas where the light conditions are favorable. The negative phototactic organisms avoid the lighted layers of water during the day and only rise to the surface at night. Freshwater crabs like Daphnia hyalina perform vertical hikes of up to 60 m.

The plankton is divided into the following size classes: Femto-P: < 0,2 μm="" (viren);="">Pico-P .: 0.2-2 μm (bacteria, flagellates); Nano-P .: 2 - 20 μm, Micro-P .: 20 - 200 μm (cyanobacteria, algae, protozoa, metazoan larvae); Meso-P .: 0.2 - 20 mm, Macro P .: 2 - 20 cm; Mega-P .: 20 - 200 cm (algae, protozoa, metazoa and their larvae). According to the systematic assignment, one differentiates Phytoplankton, Zooplankton and Bacterioplankton. As Meroplankton is the term used for the P. that only spends certain life stages in the pelagic region, such as the larvae of the triangular mussel (Dreissena). In most organisms of P., however, the entire life cycle takes place in the pelagic region (Holoplankton).

To the P. of the lakes include viruses, bacteria, algae, amoebas (Amoebina), sun animals (Heliozoa), ciliates (Ciliata), rotifers (Rotatoria), leaf pods (Branchiopoda) and copepods (Copepoda), the freshwater medusa Craspedacusta, the larvae of the triangular mussel (Dreissena) and Chaoborus-Larvae. (see fig.)

The marine P. consists of viruses, bacteria (e.g. cyanobacteria), diatoms (Bacillariophyceae), dinoflagellates (Dinophyta), calcium flagellates (Coccolithophorales), floating brown algae (e.g. Sargassum fluitans), planktonically living larvae (e.g. of polychetes, crustaceans, mollusks, echinoderms and fish), jellyfish (medusa), flagellates (flagellata), ciliate (ciliata), chamberlings (foraminifera), radiolucent animals (radiolaria), crustaceans, salps, fire rollers and Appendicularia. Mollusks like pinnipeds and planktonic hind gill snails are of great importance for the nutrition of fish and whales. An important source of food for marine organisms is Krill (Eucarida). (see fig.)

The Phyto-P. and the species of phototrophic bacteria belonging to P. (including cyanobacteria) make a significant contribution to aquatic primary production and thus to the release of oxygen (“Source for O2") To the atmosphere and for the uptake of carbon dioxide (" sink for CO2“) From the atmosphere. The Phyto-P. Outgoing food chains usually lead to the necton via the zooplankton. The diet of the heterotrophic P. consists of detritus, bacteria or animal and plant organisms. In most cases, the surrounding water is filtered at random through filter devices and the residue is fed to the mouth opening in whole or after sorting. Over a longer food chain, many fish and whales are directly or indirectly dependent on the P. for their diet. A large part of the deep-sea animals is dependent on the constant supply of dead plankton organisms.