Marine fungi are species of fungi that live in marine or estuarine environments. They are not a taxonomic group, but share a common habitat. Obligate marine fungi grow exclusively in the marine habitat while wholly or sporadically submerged in sea water. Facultative marine fungi normally occupy terrestrial or freshwater habitats, but are capable of living or even sporulating in a marine habitat.
Marine fungi account for about 5% of the total ocean biomass. About 2,149 species of marine fungi have been described, within eleven phyla and 856 genera, although only about 64 species have been fully genetically sequenced.Jones, EB Gareth et al. Marine Fungi. Originally published May 17, 2019. Last updated February 27, 2025. Accessed April 2, 2025. Many species of marine fungi are known only from spores and it is likely a large number of species have yet to be discovered. It has been estimated that less than 1% of all marine fungal species have been described, due to difficulty in targeting marine fungal DNA and difficulties that arise in attempting to grow cultures of marine fungi. It is impracticable to culture many of these fungi, but their nature can be investigated by examining seawater samples and undertaking rDNA analysis of the fungal material found.
Different marine habitats support very different fungal communities. Fungi can be found in niches ranging from ocean depths and coastal waters to mangrove swamps and estuaries with low salinity levels. Marine fungi can be saprobic or parasitic on animals, saprobic or parasitic on algae, saprobic on plants, or saprobic on dead wood.Species of Higher Marine Fungi University of Mississippi. Retrieved 2012-02-05.
There has been some debate as to what exactly a marine fungus should be defined as. A definition used previously was "individuals with a long-term presence and metabolic activities in a marine habitat." A more commonly used definition nowMitchison-Field, Lorna; et al. (June 2, 2019). "Unconventional cell division cycles from marine-derived yeasts". Current Biology. is from Ka-Lai et al. 2016: "any fungus that is recovered repeatedly from marine habitats because: 1) it is able to grow and/or sporulate (on substrata) in marine environments; 2) it forms symbiotic relationships with other marine organisms; or 3) it is shown to adapt and evolve at the genetic level or be metabolically active in marine environments."
Overview Terrestrial fungi play critical roles in nutrient cycling and food webs and can shape macroorganism communities as parasites and mutualists. Although estimates for the number of fungal species on the planet range from 2.2 to 3.8 million species, likely fewer than 10% of fungi have been identified so far, being around 150,000. To date, a relatively small percentage of described species are associated with marine environments, with ~2,200 species retrieved exclusively from the marine environment. Nevertheless, fungi have been found in nearly every marine habitat explored, from the surface of the ocean to kilometers deep in ocean sediments. Fungi are hypothesized to contribute to phytoplankton population cycles and the biological carbon pump and are active in the chemistry of marine sediments. Many fungi have been identified as commensals or pathogens of marine animals, like corals, sponges, and other marine organisms like plants, and algae. Despite their varied roles, remarkably little is known about the diversity of this major branch of eukaryotic life in marine ecosystems or their ecological functions. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Fungi represent a large and diverse group of microorganisms in microbiological communities in the marine environment and have an important role in nutrient cycling.Tisthammer, K.H.; Cobian, G.M.; Amend, A.S. Global biogeography of marine fungi is shaped by the environment. Fungal Ecol. 2016, 19, 39–46. They are divided into two major groups; obligate marine fungi and facultative marine fungi.Raghukumar, S. The marine environment and the role of fungi. In Fungi in Coastal and Oceanic Marine Ecosystems: Marine Fungi; Springer International Publishing: Cham, Switzerland, 2017; pp. 17–38. Obligate marine fungi are adapted to reproduce in the aquatic environment, while facultative marine fungi can grow in aquatic as well as terrestrial environments. Marine fungi are called marine-derived fungi when their facultative or obligate state is not certain.Patyshakuliyeva, A., Falkoski, D.L., Wiebenga, A., Timmermans, K. and De Vries, R.P. (2020) "Macroalgae derived fungi have high abilities to degrade algal polymers". Microorganisms, 8(1): 52. . Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Marine fungal species occur as saprobes, parasites, or symbionts and colonize a wide range of substrates, such as sponges, corals, mangroves, seagrasses and algae.Jones, E.B.G.; Suetrong, S.; Sakayaroj, J.; Bahkali, A.H.; Abdel-Wahab, M.A.; Boekhout, T.; Pang, K.-L. Classification of marine Ascomycota, Basidiomycota, Blastocladiomycota and Chytridiomycota. Fungal Divers. 2015, 73, 1–72.Debbab, A.; Aly, A.H.; Proksch, P. Mangrove derived fungal endophytes–a chemical and biological perception. Fungal Divers. 2013, 61, 1–27. Factors that influence whether or not marine fungi are present in any particular location include the water temperature, its salinity, the water movement, the presence of suitable substrates for colonization, the presence of propagules in the water, interspecific competition, pollution and the oxygen content of the water. Some marine fungi which have ventured into the sea from terrestrial habitats include species that burrow into sand grains, living in the pores. Others live inside stony corals, and may become pathogenic if the coral is stressed by rising sea temperatures.
In 2011 the phylogeny of marine fungi was elucidated by analysis of their small subunit ribosomal DNA sequences. Thirty six new marine lineages were found, the majority of which were chytrids but also some filamentous and multicellular fungi. The majority of the species found were ascomycetous and basidiomycetous yeasts. The secondary metabolites produced by marine fungi have high potential for use in biotechnological, medical and industrial applications.Marine Fungi Retrieved 2012-02-06.
The ocean constitutes about 99% of the volume in the biosphere. Oceanic microbes comprise 70%–90% of the biomass of marine biota Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License and are the main drivers of marine biogeochemical cycles. They are responsible for determining the amount of carbon fixed during photosynthesis, the subsequent release of carbon back to CO2 through respiration, and ultimately the sequestration of carbon in the deep ocean over millennial scales. Present estimates of marine microbial biomass primarily rely on bacteria, archaea, and protists. Pelagic (planktonic) fungal biomass has been less studied and only superficially characterized, despite their recently documented ubiquitous presence and active participation in the marine carbon and nitrogen cycles.
As of 2025, only a few studies are available on pelagic fungal biomass, restricted to distinct coastal areas, and an accurate representation of the vast open-ocean environment is still lacking. These studies are based on different methods, each with their own limitations hampering robust intercomparison of results. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Among the biomass of organisms/groups estimated in the ocean, fungi accounted for the highest uncertainty, ranging more than two orders of magnitude, indicating the need for a direct estimate of fungal biomass in the ocean. There is need for large-scale sampling across biogeographical provinces in the open ocean to ensure precise quantification of pelagic fungi in the microbial biomass.
Evolution In contrast to plants and animals, the early fossil record of the fungi is meager. Since fungi do not biomineralise, they do not readily enter the fossil record. Fungal fossils are difficult to distinguish from those of other microbes, and are most easily identified when they resemble extant fungi.
The earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some (Ma). These multicellular benthic organisms had filamentous structures capable of anastomosis, in which hyphal branches recombine. Other recent studies (2009) estimate the arrival of fungal organisms at about 760–1060 Ma on the basis of comparisons of the rate of evolution in closely related groups.
For much of the Paleozoic Era (542–251 Ma), the fungi appear to have been aquatic and consisted of organisms similar to the extant Chytrids in having flagellum-bearing spores. Phylogenetic analyses suggest that the flagellum was lost early in the evolutionary history of the fungi, and consequently, the majority of fungal species lack a flagellum. Evidence from DNA analysis suggests that all fungi are descended from one common ancestor, at least 600 million years ago. It is probable that these earliest fungi lived in water, and had flagella. Fungi moved to land at about the same time as plants, about 460 million years ago, at least. Although fungi are opisthokonts—a grouping of evolutionarily related organisms broadly characterized by a single posterior flagellum—all phyla except for the chytrids have lost their posterior flagella.
The evolutionary adaptation from an aquatic to a terrestrial lifestyle necessitated a diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships such as mycorrhiza and lichenization.Taylor and Taylor, pp. 84–94 and 106–107. Recent (2009) studies suggest that the ancestral ecological state of the Ascomycota was saprobism, and that independent lichenization events have occurred multiple times.
The growth of fungi as hyphae on or in solid substrates or as single cells in aquatic environments is adapted for the efficient extraction of nutrients, because these growth forms have high surface area to volume ratios. Hyphae are specifically adapted for growth on solid surfaces, and to invade substrates and tissues. They can exert large penetrative mechanical forces; for example, many plant pathogens, including Magnaporthe grisea, form a structure called an appressorium that evolved to puncture plant tissues. The pressure generated by the appressorium, directed against the plant epidermis, can exceed . The filamentous fungus Paecilomyces lilacinus uses a similar structure to penetrate the eggs of nematodes.
Fungi were considered to be part of the plant kingdom until the mid-20th century. By the middle of the 20th century, fungi were considered a distinct kingdom, and the newly recognized kingdom Fungi becoming the third major kingdom of multicellular eukaryotes with kingdom Plantae and kingdom Animalia, the distinguishing feature between these kingdoms being the way they obtain nutrition.
Planktonic marine fungi
Marine plankton are organisms that drift in the ocean but are unable to actively propel themselves against currents. Planktonic marine fungi are found drifting in the marine water column in the form of spores, yeasts, mycelia, sporangia or other fungal propagules, in suspension or attached to particles, substrates or planktonic hosts. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
Food webs and the mycoloop