Aquatic Microbiology Textbook

Aquatic microbiology can be defined as the study of microorganisms and microbial communities in water environments.

Aquatic habitats range from the vast ocean reaches to lakes and flowing bodies of water,such as rivers, streams, estuaries, wetlands, springs, and aquifers. Roughly 71% of the Earth’s surface is occupied by water,>97% of which is contained in the world’s oceans. Less than 1% of water is foundin streams, rivers, and lakes. Water in all these different aquatic habitats is constantlybeing renewed through the hydrologic cycle. Thesize and diversity of aquatic habitats hints at the importance of aquatic habitats formicroorganisms. Major microbial players in aquatic habitats include phototrophs, whichare critical to primary production, and heterotrophs, which participate in the cycling ofcarbon in aquatic habitats.

Microorganisms are key components of the aquatic environment. As the most important primary producers, microorganisms are responsible for photosynthetic fixation of carbon dioxide into organic matter.

Aquatic primary production is estimated to be approximately 50% of all primary production on earth. As will be seen, microorganisms are also the most important consumers responsible for harvesting the organic matter produced through primary production and respiring it back into carbon dioxide.

Life in aquatic environment (freshwater and marine) has numerous potential advantages over terrestrial existence. These include physical support (buoyancy), accessibility of three-dimensional space, passive movement by water currents, dispersal of motile gametes in a liquid medium, minimal loss of water (freshwater systems), lower extremes of temperature and solar radiation, and ready availability of soluble organic and inorganic nutrients.

Potential disadvantages of aquatic environments include osmotic differences between the organism and the surrounding aquatic medium (leading to endosmosis and exosmosis) and a high degree of physical disturbances in many aquatic systems. In undisturbed aquatic systems such as lakes, photosynthetic organisms have to maintain their position at the top of the water column for light availability. In many water bodies (e.g. lake water column), physical and chemical parameters show a continuum – with few distinct microhabitats. In these situations, species compete in relation to different growth and reproductive strategies rather than specific adaptations to localized environmental conditions.