marine fungi

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. About 444 species of marine fungi have been described, including seven genera and ten species of basidiomycetes, and 177 genera and 360 species of ascomycetes. The remainder of the marine fungi are chytrids and mitosporic or asexual fungi.Species of Higher Marine Fungi
University of Mississippi. Retrieved 2012-02-05. Many species of marine fungi are known only from spores and it is likely a large number of species have yet to be discovered. In fact, it is thought 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.

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 1.5 to over 5 million, likely fewer than 10% of fungi have been identified so far. To date, a relatively small percentage of described species are associated with marine environments, with ∼1,100 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 below 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 (e.g., corals and sponges), 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.Amend, A., Burgaud, G., Cunliffe, M., Edgcomb, V.P., Ettinger, C.L., Gutiérrez, M.H., Heitman, J., Hom, E.F., Ianiri, G., Jones, A.C. and Kagami, M. (2019
"Fungi in the marine environment: Open questions and unsolved problems"
''MBio'', 10(2): e01189-18. . Modified text was copied from this source, which is available under
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. 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
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.

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.

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. Recent (2009) studies suggest that the ancestral ecological state of the Ascomycota was saprobism, and that independent lichen 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.

Marine plants

Mangroves

The greatest number of known species of marine fungi are from mangrove swamps. In one study, blocks of mangrove wood and pieces of driftwood of '' Avicennia alba'', '' Bruguiera cylindrica'' and '' Rhizophora apiculata'' were examined to identify the lignicolous (wood-decaying) fungi they hosted. Also tested were ''Nypa fruticans'', a mangrove palm and '' Acanthus ilicifolius'', a plant often associated with mangroves. Each material was found to have its own characteristic fungi, the greatest diversity being among those growing on the mangrove palm. It was surmised that this was because the salinity was lower in the estuaries and creeks where ''Nypa'' grew, and so it required a lesser degree of adaptation for the fungi to flourish there. Some of these species were closely related to fungi on terrestrial palms. Other studies have shown that driftwood hosts more species of fungus than do exposed test blocks of wood of a similar kind. The mangrove leaf litter also supported a large fungal community which was different from that on the wood and living material. However, few of these were multicellular, higher marine fungi.

Other plants

The sea snail '' Littoraria irrorata'' damages plants of '' Spartina'' in the coastal sea marshes where it lives, which enables spores of intertidal ascomycetous fungi to colonise the plant. The snail eats the fungal growth in preference to the grass itself. This mutualism between the snail and the fungus is considered to be the first example of husbandry among invertebrate animals outside the class Insecta.

Eelgrass, ''Zostera marina'', is sometimes affected by seagrass wasting disease. The primary cause of this seems to be pathogenic strains of the protist ''Labyrinthula zosterae'', but it is thought that fungal pathogens also contribute and may predispose the eelgrass to disease.

Wood

Many marine fungi are very specific as to which species of floating and submerged wood they colonise. A range of species of fungi colonise beech, while oak supports a different community. When a fungal propagule lands on a suitable piece of wood, it will grow if no other fungi are present. If the wood is already colonised by another fungal species, growth will depend on whether that fungus produces antifungal chemicals and whether the new arrival can resist them. The chemical properties of colonizing fungi also affect the animal communities that graze on them: in one study, when hyphae from five different species of marine fungi were fed to nematodes, one species supported less than half the number of nematodes per mg of hyphae than did the others.

Detection of fungi in wood may involve incubation at a suitable temperature in a suitable water medium for a period of six months to upward of eighteen months.

Lichens

Lichen

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