marine microorganisms marine microorganisms marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. a microorganism (or microbe) is any microscopic living organism or virus, that is too small to see with the unaided human eye without magnification. microorganisms are very diverse. they can be single-celled or multicellular and include bacteria, archaea, viruses and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. many macroscopic animals and plants have microscopic juvenile stages. some microbiologists also classify viruses as microorganisms, but others consider these as non-living. role of the microbial community in the marine carbon cycle marine microorganisms have been variously estimated to make up about 70%, or about 90%, of the biomass in the ocean. taken together they form the marine microbiome. over billions of years this microbiome has evolved many life styles and adaptations and come to participate in the global cycling of almost all chemical elements. microorganisms are crucial to nutrient recycling in ecosystems as they act as decomposers. they are also responsible for nearly all photosynthesis that occurs in the ocean, as well as the cycling of carbon, nitrogen, phosphorus and other nutrients and trace elements. marine microorganisms sequester large amounts of carbon and produce much of the world's oxygen. a small proportion of marine microorganisms are pathogenic, causing disease and even death in marine plants and animals. however marine microorganisms recycle the major chemical elements, both producing and consuming about half of all organic matter generated on the planet every year. as inhabitants of the largest environment on earth, microbial marine systems drive changes in every global system. in july 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (luca) of all life on the planet, including the marine microorganisms. despite its diversity, microscopic life in the oceans is still poorly understood. for example, the role of viruses in marine ecosystems has barely been explored even in the beginning of the 21st century. part of a series of overviews onmarine life marine habitats marine microorganisms marine microbiomes marine viruses marine prokaryotes marine protists marine fungi marine invertebrates marine vertebrates marine primary production marine food web marine carbon pump marine biogeochemical cycles human impact on marine life marine conservation marine life portal part of a series onplankton trophic mode phytoplankton zooplankton mixoplankton mycoplankton bacterioplankton virioplankton by size heterotrophic picoplankton microalgae microzooplankton nanophytoplankton calcareous photosynthetic picoplankton picoeukaryote picoplankton marine microplankton by taxonomy algae diatoms coccolithophores dinoflagellates protozoans radiolarians foraminiferans amoebae ciliates bacteria cyanobacteria archaea viruses by habitat aeroplankton geoplankton marine plankton prokaryotes protists freshwater plankton other types gelatinous zooplankton holoplankton ichthyoplankton meroplankton pseudoplankton tychoplankton blooms algal bloom critical depth cyanobacterial bloom harmful algal bloom spring bloom eutrophication great atlantic sargassum belt great calcite belt milky seas effect related topics algaculture claw hypothesis cpr diel vertical migration f-ratio marine primary production ocean fertilization iron paradox of the plankton planktivore planktology thin layers naames category overview microbial matsmicrobial mats are the earliest form of life on earth for which there is good fossil evidence. the image shows a cyanobacterial-algal mat.stromatolites are formed from microbial mats as microbes slowly move upwards to avoid being smothered by sediment. while recent technological developments and scientific discoveries have been substantial, we still lack a major understanding at all levels of the basic ecological questions in relation to the microorganisms in our seas and oceans. these fundamental questions are: 1. what is out there? which microorganisms are present in our seas and oceans and in what numbers do they occur? 2. what are they doing? what functions do each of these microorganisms perform in the marine environment and how do they contribute to the global cycles of energy and matter? 3. what are the factors that determine the presence or absence of a microorganism and how do they influence biodiversity and function and vice versa? – european science foundation, 2012: 14 microorganisms make up about 70% of the marine biomass. a microorganism, or microbe, is a microscopic organism too small to be recognised adequately with the naked eye. in practice, that includes organisms smaller than about 0.1 mm.: 13 such organisms can be single-celled or multicellular. microorganisms are diverse and include all bacteria and archaea, most protists including algae, protozoa and fungal-like protists, as well as certain microscopic animals such as rotifers. many macroscopic animals and plants have microscopic juvenile stages. some microbiologists also classify viruses as microorganisms, but others consider these as non-living. microorganisms are crucial to nutrient recycling in ecosystems as they act as decomposers. some microorganisms are pathogenic, causing disease and even death in plants and animals. as inhabitants of the largest environment on earth, microbial marine systems drive changes in every global system. microbes are responsible for virtually all the photosynthesis that occurs in the ocean, as well as the cycling of carbon, nitrogen, phosphorus and other nutrients and trace elements. marine microorganisms viruses prokaryotes bacteria archaea eukaryotes protists microfungi microanimals relative sizes of microscopic entities the range of sizes shown by prokaryotes (bacteria and archaea) and viruses relative to those of other organisms and biomolecules sea spray containing marine microorganisms can be swept high into the atmosphere where they become aeroplankton, and can travel the globe before falling back to earth. under a magnifier, a splash of seawater teems with microscopic life microscopic life undersea is diverse and still poorly understood, such as for the role of viruses in marine ecosystems. most marine viruses are bacteriophages, which are harmless to plants and animals, but are essential to the regulation of saltwater and freshwater ecosystems. they infect and destroy bacteria in aquatic microbial communities, and are the most important mechanism of recycling carbon in the marine environment. the organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth. viral activity may also contribute to the biological pump, the process whereby carbon is sequestered in the deep ocean. a stream of airborne microorganisms circles the planet above weather systems but below commercial air lanes. some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in sea spray. in 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet. microscopic organisms live throughout 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). single-celled barophilic marine microbes have been found at a depth of 10,900 m (35,800 ft) in the mariana trench, the deepest spot in the earth's oceans. microorganisms live inside rocks 580 m (1,900 ft) below the sea floor under 2,590 m (8,500 ft) of ocean off the coast of the northwestern united states, as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off japan. the greatest known temperature at which microbial life can exist is 122 °c (252 °f) (methanopyrus kandleri). in 2014, scientists confirmed the existence of microorganisms living 800 m (2,600 ft) below the ice of antarctica. according to one researcher, "you can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are." marine microorganisms serve as "the foundation of all marine food webs, recycling major elements and producing and consuming about half the organic matter generated on earth each year". marine viruses virus-host interactions in the marine ecosystem,including viral infection of bacteria, phytoplankton and fish a virus is a small infectious agent that replicates only inside the living cells of other organisms. viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. when not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. these viral particles, also known as virions, consist of two or three parts: (i) the genetic material (genome) made from either dna or rna, long molecules that carry genetic information; (ii) a protein coat called the capsid, which surrounds and protects the genetic material; and in some cases (iii) an envelope of lipids that surrounds the protein coat when they are outside a cell. the shapes of these virus particles range from simple helical and icosahedral forms for some virus species to more complex structures for others. most virus species have virions that are too small to be seen with an optical microscope. the average virion is about one one-hundredth the size of the average bacterium. the origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of dna that can move between cells—while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity. viruses are considered by some to be a life form, because they carry genetic material, reproduce, and evolve through natural selection. however, they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life" and as replicators. bacteriophages (phages)multiple phages attached to a bacterial cell wall at 200,000x magnification diagram of a typical tailed phage phage injecting its genome into bacteria viruses are found wherever there is life and have probably existed since living cells first evolved. the origin of viruses is unclear because they do not form fossils, so molecular techniques have been used to compare the dna or rna of viruses and are a useful means of investigating how they arose. viruses are now recognised as ancient and as having origins that pre-date the divergence of life into the three domains. opinions differ on whether viruses are a form of life or organic structures that interact with living organisms. they are considered by some to be a life form, because they carry genetic material, reproduce by creating multiple copies of themselves through self-assembly, and evolve through natural selection. however they lack key characteristics such as a cellular structure generally considered necessary to count as life. because they possess some but not all such qualities, viruses have been described as replicators and as "organisms at the edge of life". phages virions of different families of tailed phages these are cyanophages, viruses that infect cyanobacteria (scale bars indicate 100 nm) bacteriophages, often just called phages, are viruses that parasite bacteria and archaea. marine phages parasite marine bacteria and archaea, such as cyanobacteria. they are a common and diverse group of viruses and are the most abundant biological entity in marine environments, because their hosts, bacteria, are typically the numerically dominant cellular life in the sea. generally there are about 1 million to 10 million viruses in each ml of seawater, or about ten times more double-stranded dna viruses than there are cellular organisms, although estimates of viral abundance in seawater can vary over a wide range. for a long time, tailed phages of the order caudovirales seemed to dominate marine ecosystems in number and diversity of organisms. however, as a result of more recent research, non-tailed viruses appear to be dominant in multiple depths and oceanic regions, followed by the caudovirales families of myoviruses, podoviruses, and siphoviruses. phages belonging to the families corticoviridae, inoviridae, microviridae, and autolykiviridae are also known to infect diverse marine bacteria. there are also archaean viruses which replicate within archaea: these are double-stranded dna viruses with unusual and sometimes unique shapes. these viruses have been studied in most detail in the thermophilic archaea, particularly the orders sulfolobales and thermoproteales. role of viruses microorganisms make up about 70% of the marine biomass. it is estimated viruses kill 20% of this biomass each day and that there are 15 times as many viruses in the oceans as there are bacteria and archaea. viruses are the main agents responsible for the rapid destruction of harmful algal blooms, which often kill other marine life. the number of viruses in the oceans decreases further offshore and deeper into the water, where there are fewer host organisms. viruses are