Marine life live in the water column of large bodies of water and that cannot swim against a current. They provide a crucial source of food to many large aquatic organisms, such as fish and whales. These organisms include drifting or floating bacteria, archaea, algae, protozoa and animals that inhabit, for example, the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification. Though many planktonic species are microscopic in size, "plankton" includes organisms covering a wide range of sizes, including large organisms such as jellyfish. The
Marine microorganism their importance in ecosystems, particularly marine ecosystems, has been underestimated, leading to these infectious agents being poorly investigated and their numbers and species biodiversity being greatly under reported. Microscopic organisms live in every part of the biosphere. The mass of prokaryote microorganisms — which includes bacteria and archaea, but not the nucleated eukaryote microorganisms — may be as much as 0.8 trillion tons of carbon (of the total biosphere mass, estimated at between 1 and 4 trillion tons). Barophilic marine microbes have been found at more than a depth of in the Mariana Trench, the deepest spot in the Earth's