Introduction:
The neritic zone is the region of shallow water that is 200 meters above the continental shelf. it is present near shore, where light penetrates depth to the sea floor. The literal zone includes the intertidal zone. The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide.
Neritic and littoral habitats differ from oceanic habitats. Nutrients present at a high level than in oceans, Organic compounds are more intense and 90 percent of bacterial degradation occurs here. High light intensities lead to extensive development of plant communities.
Primary plant production is at a high level enhanced by rapid regeneration of inorganic nutrients. Bacteria are involved in geochemical cycles such as carbon, nitrogen, sulfur phosphorus, trace minerals cycle, etc. cyanobacteria, and prokaryotes form extensive mat communities which are important in nitrogen fixation and photosynthesis. Microorganisms present in the water column are also present in this zone.
Occurrence of pathogenic bacteria:
vibrio is present more in this zone. V. cholera, V. Parahemolyticus are human pathogens found here. The latter is called a marine enteric organism and is associated with shellfish and clams.
This has public health concern since shellfish are eaten raw. Vibrio vulnificus is present in fin fish and is also a concern because fin fish travel long distances and introduce the pathogen to new areas.
Luminescent bacteria:
Luminescent symbiosis is common in this zone. The luminescent bacteria Vibrio fischeri forms symbiotic associations with fish and other mollusk animals. In bioluminescent symbiosis bacteria harbored in pure cultures in light organs and receive nutrients from the fish. Bacteria also benefit from the exclusion of competitors’ dissemination of light organs into new habitats.
The animals use light for feeding, signaling, and antipredation. In light organs, bacteria grow more slowly than in lab cultures 20 to 30 times slower. In V. fischeri luciferase synthesis and resulting luminescence are controlled by autoinduction. Contro by autoinducer N-homoserine lactone which acts as a bacterial pheromone. the synthesis of luciferase enzyme is triggered by the conc of the autoinducer reaching a threshold level ( 107 per ml ) So the symbiosis results because in seawater the autoinducer will not expect to cross the threshold level where cell densities are less than 100 per ml.
Benifit of luminescence
It’s preferable over a saprophytic or free-living lifestyle because it enhances dispersal. The organism will attract to food sources by light production. Luciferase enzyme act as an alternative to electron acceptor so bacteria can grow at low oxygen concentration.
Other microorganisms:
Cytophaga is common in the near-shore environment and is important because of its cellulolytic microflora. Streptomyces are also present. Micro aerophilic occurs at a level of 100 to 50 percent. Magnetotactic and microaerophilic isolated from coastal environments.
Oxic and Anoxic layers:
Neritic and littoral sediments are recognized as sites of intense microbial activity. High deposition of organic matter means the depletion of oxygen occurs within sediments a few mm from the surface. In oceans, sediments are oxic for many meters. Bacteria play an important role in anoxic mineralization. A high quantity of sulfate is present which means sulfate-reducing bacteria are present in abundance and account for 70% of mineralization in the sediments. The H2S produced by sulfate reduction then reacts with iron or Manganese and diffuses upward in the oxic zone. Microbial mat communities formed on the sediment surface. These consist of vertically stratified communities that cover large areas of mud flats sea marshes and upper intertidal regions of sandy beaches.
The bacteria common are those that metabolize sulfur compounds and elemental sulfur. Overlap occurs between H2S and oxygen. Chemolithotrophic autotrophs that tolerate H2S are present in the H2S – O2 interface and fix Nitrogen and carbon dioxide.
Purple sulfur Bacteria:
Just beneath H2S anoxygenic purple sulfur bacteria are present. which oxidizes H2s and fixes CO2 and N2. They obtain electron donors from incomplete sulfur oxidation by thiobacillus.
Green sulfur bacteria are present in the underlying layer.
On the bottom layer of the mat sulfate-reducing bacteria are present on the surface of the mat cyanobacteria are present. sulfide tolerant cyanobacteria may present along with purple sulfur bacteria.
Effect of UV:
Cyanobacteria are sensitive to Highly intense UV radiations. Due to ozone depletion UV increases. causes the shifting of cyanobacteria from the upper surface to the downward. And disturbs primary production. Oxidation and reduction of thiosulphate occur throughout the mat, however, Oxidation occurs in oxidation prominent in the oxic layer and reduction in anoxic.
Dynamic habitat.
Sediments are dynamic and physiochemical conditions change rapidly. Oxygen concentration falls rapidly at sunset and free sulfide ion moves to the surface and water column. this process is reversed at dawn and a visible change of color of sediments of water occurs.
The tidal state also determines the free sulfide on the surface layers of sediments. the sulfide generated at depths of 20 to 30mm in sediments being available to purple sulfur bacteria. this cyclic movement of sulfide ions results in blooms of Thiocapsa.
Pyrites formation:
In the suboxic zone, the oxidation of organic compounds by Fe and Mn occurs. the H2S reacts with Fe to form FeS which forms pyrites. Pyrites are reoxidized by oxygen on a seasonal basis. In coastal sediments, reoxidation occurs in winter, and in marshes, it occurs in summer.
Methanogenesis also occurs. High levels of sulfate reduction cause sewage pollution. Sulfate-reducing bacteria in biofilms cause metal corrosion. Incomplete oxidation of H2S causes the death of fish.