Microbial loop
The microbial loop ( from the English: microbial loop) describes a material cycle in the food web of marine plankton, are added to the dissolved organic carbon compounds by bacteria and passed along the classical food chain phytoplankton - zooplankton - nekton. The term microbial loop was by Farooq Azam et al. (1983 ) coined to describe the importance of bacteria in the biogeochemical cycles of marine ecosystems.
Dissolved organic carbon compounds probably added from the microbial degradation of organic particles and detritus, or be specifically stated as waste products of plant and animal cells. Especially small organic molecules can also inadvertently escape from cells. Heterotrophic bacteria break down organic particles and cleave macromolecules such as polysaccharides, fats and proteins into simple monomers in order to respire for energy or to create your own cell substance of it. Thus, the organic carbon and the energy stored in the rest of the ecosystem is available.
History
Before the discovery of the microbial loop, the marine food web was considered as a shortcut linear food chains in the carbon and energy by primary producers (phytoplankton ) was fixed, these primary production be utilized by herbivores, which in turn are eaten by predators. All these organisms are ultimately degraded by heterotrophic bacteria, which release the contained elements as inorganic compounds. Heterotrophic bacteria in water were not considered to be significant consumers of organic matter. Traditional methods for the enumeration of bacteria (for example, by culturing on agar plates ) showed only very small numbers of cells, so that the influence of the bacteria was seen in early studies on the marine ecology be very low. This changed when new methods, such as epifluorescence microscopy led to significantly higher estimates of bacterial density. These observations led to a reassessment of the importance of bacteria for the marine ecosystem. The term " microbial loop " was by Azam et al. (1983 ) coined, who pointed out that bacterivorous protists belonging to the same size class as phytoplankton and therefore likely to be an important part of the diet of planktonic crustaceans.
Factors
The efficiency of the microbial loop is determined by the population density of the marine bacteria. The bacterial density in turn is controlled by the grazing by protozoa and different classes of bacteria -eating ( bacterivorous ) flagellates. In addition, the bacteria also cause infections with viruses, destruction of bacterial cells, which in turn organic compounds are released into the water. The common effect of protozoa and viruses compensates for most of the bacterial population growth, whereby bacteria can be suppressed flowering.
Importance to the marine ecosystem
The microbial loop is of particular importance, since they dissolved organic carbon compounds are used which are not usable for most other organisms, thereby reducing the overall efficiency of the ecosystem is increased. The dissolved organic matter are recycled and not degraded to mineral compounds. Same time, other nutrients (eg, phosphorus, nitrogen) are recycled that would otherwise sink into unreachable depth so that the microbial loop of the coast is of particular importance far in nutrient-poor waters. Where the biomass of microbial loop corresponds to the five to ten times the biomass of all multicellular organisms (such as fish). Heterotrophic bacteria then form the basis of the food web of many oceanic ecosystems dar. Heterotrophic bacteria use up to 50% of net primary production order.
The work of Kerner et al. (2003) supplemented the microbial loop to the process of abiotic aggregation of dissolved organic substances to particles ( flocculation). These particles can be directly absorbed by bacterivorous protists otherwise. Heterotrophic bacteria respire about 30 % of ingested organic carbon and thus represent only about two-thirds as biomass available. Abiotic aggregation avoids the loss due to bacterial respiration, thereby increasing the efficiency of recycling.