Advances in influence of seawater eutrophication on marine bacteria

Input of excessive macronutrients (e. g., nitrogen or phosphorus) and organic matter results in a change in the trophic status of a body of water, and leads to eutrophication in the coastal sea areas. In response to these changes, the biological community, particularly the microbial community, will alter. Microorganisms are sensitive and easily influenced by eco-factors such as temperature, organic matter, etc, in which marine heterotrophic bacteria are able to utilize dissoluble organic matter to perform a "second production" coupling with the classic grazing food chain, and causing a cycle of matter. Multiple measurement methods indicate that the abundance and biomass of bacterioplankton are greater in eutrophic coastal areas than in normal and clean sea areas. Furthermore, with the intensifying eutrophication of seawater, the concentration of chlorophyll a increases in the water body, enabling rapid growth and resulting in significant biomass of bacterioplankton. To date, the population density and biomass of bacterioplankton have not been found to decline with the eutrophication of seawater. Bacterial physiological groups include species that carry out the same function but exhibit different morphological characteristics and belong to different taxa; these groups are closely associated with eutrophication and include nitrifying bacteria, denitrifying bacteria, coliform bacteria, anaerobic sulfate-reducing bacteria, and methanogens and so on. The processes of nitrification and denitrification intensify in a manner that is not in proportion with increasing eutrophication in coastal areas or bays; therefore, nitrifying and denitrifying bacteria are more abundant in aquatic, in particular benthic, habitats. The presence of sulfate-reducing bacteria and methanogens indicates an anaerobic habitat; in addition, their population densities directly respond to an anaerobic status to some extent. Eutrophication of a water body easily leads to an anaerobic habitat and a lower oxidation-reduction potential, favoring the growth and reproduction of sulfate-reducing bacteria. The methanogen population will subsequently increase in extremely anaerobic habitats, especially benthic sediments. Coliform bacteria are microbial indicators of the marine environment, and their population indicates the extent of eutrophication on the basis of leading factors resulting from land input in coastal areas. Therefore, almost all studies show that the population of coliform bacteria d