ABSTRACT

Introduction Aquatic environments range from the pristine stream emerging from the mountain top to the chimneys of hydrothermal vents in the deepest parts of the ocean. At the same time, ecosystem habitats may range in size from microniches on small pieces of particulate matter to stratified lakes and microbial mat communities. It has, however, been argued that, with the exception of specialized microorganisms, the ecology of marine and freshwater micro-organisms is similar. The extent to which this is true is debatable, but some microbiologists consider that micro-organisms of marine and freshwater origin coexist in estuarine and inshore environments where fresh water and sea water mix. Further evidence is required for a full understanding of the situation. It is established, however, that there are many common features of life in photic aquatic communities where algae and cyanobacteria are of much greater importance in primary production than in most terrestrial environments.