Let's discuss microbial ecology in marine ecosystems. Now freshwater and saltwaterhabitats provide really great diverse environments for microbial organisms. Marinemicrobes in particular are known to contribute over half of the planet'sproductivity in biomass. So the planet really relies a lot on marine microbes tosupport ecosystems activities. Also, a lot of marine microbes and freshwatermicrobes form the basis of the base of the food chain for a lot of other animallife. That certainly has an impact on human food sources. What we're going to takea look at in this discussion is the different areas in a marine ecosystems. Sowe're going to focus on saltwater habitats, different areas where we find microbialorganisms in saltwater habitats. And two examples of symbiotic relationships inthese marine ecosystems. So it's important to keep in mind if you take a look at atypical marine environment, there are different layers or areas in that marineecosystem where we find microbial organisms and each layer has its own distinctfeatures, as well as a unique name for that particular area. So the top tenmicrometers of ocean water is called the neuston layer. So this is really the air-water interface. So that very top, if you can imagine ten micrometers, that's verysmall thin layer, top most area of the oceanic environment. This is really wheremost microbial organisms are. So this is the area of ocean water that contains thehighest microbial concentration. And microbial concentration we're referring tobacteria and algae primarily, there certainly are some fungal organisms and someviruses as well. But we're going to focus primarily in this discussion on bacterialorganisms and algal organisms. Algae would be eukaryotic microbes. So really mostof them are found in this very top thin layer of the ocean area. And you canimagine this area gets high abundance of sunlight on a regular basis. Then directlybelow this is what's called the euphotic zone. So this is really the top one to 200meters of the ocean water. Certainly this area will still receive plenty ofsunlight. So we will find microbes that rely on sunlight for photosynthesis in thisarea of ocean water. We will also find animals that rely heavily on sunlight and onthe organisms that require sunlight in these areas as well. And directly below thatwe have aphotic zone which is about 200 to 400 meter depth of ocean water. As thename implies, aphotic zone does not receive a lot of sunlight. So in this area, wedo find microbial organisms, but the ones that require sunlight obviously would notbe able to inhabit this layer of ocean water because it doesn't receive adequatesupply of sunlight. And then the very bottom, what's called the benthos layer. Thisis the ocean floor sediment layer. Volcanic areas, a lot of thermal ventcommunities are found in this area, certainly similar to the aphotic zone. You donot find microbes in this location that require sunlight. Nor do you find animalsthat rely on microbes that require sunlight because it's really dark and lackingsunlight in these areas, in the benthos layer. Also, as you can imagine in thebenthos layer, there's very high pressure environment. So the deeper you go in theocean, the higher the pressure in terms of atmospheric pressure. So think about theterminology that we've talked about in an earlier discussion for microbes that
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