It is defined as a semi-enclosed coastal region where a river meets sea. They are transition zones between rivers and the sea which differ in both biotic and abiotic factors. They are the highly productive ecosystem on earth
Estuaries experience a tidal mixing of water from the two water-bodies and feature a characteristic salinity profile called salt wedge. The salinity ranges from full strength seawater to freshwater. The sea water, being denser due to salt concentration, sinks to the bottom while the fresh water remains on top
Due to tidal flushing, the relative amounts of freshwater and brackish water in the estuary frequently keep altering. This means that the microbial inhabitants are compelled to adapt to a constantly varying environment. This puts pressure on them in terms of maintaining a stable intracellular osmolarity in balance with the surrounding environment. Prokaryotes do so by storing compatible solutes in their cytoplasm e.g., glycerol, glycine, betaine, sucrose, mannitol, sorbitol, K+ and many other amino acids.
Microorganisms that reside in this ecosystem are mostly halotolerant that can tolerate significant changes in salt concentration. The microflora found here are – coliforms, faecalis, Aeromonas, Bacillus, Proteus, Clostridium, Sphaerotilus, Beggiatoa, Thiotrix, Thiobacillus in case the estuary receives domestic wastes rich in organic matter.
In nutritionally poor habitat, budding or appendaged bacteria may be found. Enteric viruses such as Hepatitis A virus and polio virus may be found. Some soil bacteria and fungi are likely to be found.
Besides the kind of water, tidal flushing also causes some more changes like variation from fine to coarse sediment and vice-versa. Other changes include nutrient input, pollutant and chemical concentrations
Salt Wedge
Microbial Population of Estuary
Marine populations include Roseobacter and Pelagibacter ubique
Freshwater populations include Alpha Proteobacteria, Beta Proteobacteria, Actinobacteria and Verrucomicrobia
Primary producers – Cyanobacteria like Oscillatoria, Synechococcus, chroococcoid colonies, Methanogenic archaea – Methanosarcinales and Methanomicrobiales, Sulphate reducing bacteria, phaeovibroides – green sulphur bacterium
Some microbes are indigenous while others are added from domestic, industrial, agricultural or atmospheric sources
Areas receiving domestic wastes rich in organic matter – coliforms, faecalis, Aeromonas, Bacillus, Proteus, Clostridium, Sphaerotilus, Beggiatoa, Thiotrix, Thiobacillus etc.
Intestinal virus – HIV, Polio virus
In regions that are nutritionally poor, budding and appendaged bacteria such as Hyphomicrobium, Caulobacteria, Gallionella are found
