Mycoplankton are saprotrophic or parasitic members of the

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

communities of marine and

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

ecosystems An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

. They are composed of filamentous free-living

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

and yeasts that are associated with planktonic particles or

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

. Similar to

bacterioplankton Bacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word (), meaning "wandering" or "drifting", and , a Latin term coined in the 19th century by Christian Got ...

, these aquatic fungi play a significant role in

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ic mineralization and

nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cyc ...

. Mycoplankton can be up to 20 mm in diameter and over 50 mm in length. In a typical milliliter of seawater, there are approximately 10³ to 10⁴ fungal cells. This number is greater in coastal ecosystems and

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

due to nutritional runoff from terrestrial communities. Aquatic fungi are found in a myriad of ecosystems, from mangroves, to wetlands, to the open ocean. The greatest diversity and number of species of mycoplankton is found in surface waters (< 1000 m), and the vertical profile depends on the abundance of

. Furthermore, this difference in distribution may vary between seasons due to nutrient availability. Aquatic fungi survive in a constant oxygen deficient environment, and therefore depend on oxygen diffusion by

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

and oxygen generated by photosynthetic organisms.

Classification

There is a large amount of diversity among aquatic fungi. These fungi were traditionally classified using the groupings "lower" and "higher" fungi. This has frequently been replaced with using the more precise phyla names, with "higher" fungi now roughly corresponding to the

Dikarya Dikarya is a subkingdom of Fungi that includes the divisions Ascomycota and Basidiomycota, both of which in general produce dikaryons, may be hypha, filamentous or unicellular, but are always without flagella. The Dikarya are most of the so-calle ...

subkingdom, which has the majority of the mycoplankton Genome sequencing is a common way to assess and categorize aquatic fungi. Fungi are Eukaryotes, and as such it is often the 18s rDNA which is sequenced. According to fossil records, fungi date back to the late

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

era, 900-570 million years ago. It is hypothesized that mycoplankton evolved from terrestrial fungi, likely in the

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

era (390 million years ago). It is likely that the transition from terrestrial to aquatic lifestyle has occurred many different times, as many taxa have been found with both terrestrial and marine species.

Biogeochemical contributions

There are multiple biogeochemical cycles in the Earth's oceans in which Mycoplankton play a role. They are a part of the microbial loop and other forms of nutrient cycling, including the mycoplankton specific mycoflux and mycoloop.

Cycling of organic nutrients

Mycoplankton, like all fungi, play an essential roll in the degradation of detritus and

organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

from plants, as well as other larger organisms. By working with other microbial communities, mycoplankton efficiently convert particulate organic matter to dissolved organic matter as part of biogeochemical cycling. Mycoplankton and heterotrophic bacteria mediate carbon, nitrogen, oxygen, and other nutrient fluxes in marine ecosystems. The incorporation of dissolved organic carbon into microbe biomass is what is known as the microbial loop. Mycoplankton are often found in higher abundances near the surface, as well as in shallow waters. This is indicative of a connection between mycoplankton and the upwelling of organic matter. Phytoplankton communities are also abundant in the euphotic zone, which provides further evidence for the role of Mycoplankton in consumption of organic matter.

Mycoloop and mycoflux

Mycoplankton are important in controlling

and

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

populations. The mycoloop is very similar to the microbial loop, as the basis of both is for microbes to make material accessible to organisms that occupy higher

trophic level The trophic level of an organism is the position it occupies in a food web. Within a food web, a food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the ...

s. Through the mycoloop phytoplankton are transformed such that they are able to be grazed upon by zooplankton. This function is performed by parasitic marine fungi (mycoplankton). The mycoflux is understudied, but believed to be a part of carbon capture in aquatic habitats. Functionally, this process involves aquatic fungi breaking down organic matter.

Benthic shunt

Another process which mycoplankton take part in is known as the benthic shunt. This process takes place in the

benthic zone The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

, the sediments at the bottom of the water. The benthic shunt is typically referred to in relation to freshwater aquatic environments, but the concept is relevant and takes place in marine habitats as well. The benthic shunt is basically energy and nutrient flow as directed by lower trophic level organisms, such as mycoplankton.

Role in food webs

Due to their significant contributions to nutrient cycling, mycoplankton play a large role in regulation of food webs. Aquatic fungi such as mycoplankton degrade and convert organic matter into other forms. In a way, mycoplankton contributions to aquatic food webs are the biogeochemical services that they perform. The grazer food chain and the microbial food chain are inherently intertwined, as the dissolved organic carbon at the base of the microbial food chain originally comes from material excreted by grazers from the grazer food chain. Not only are the new forms of organic matter more palatable by macro plankton, but the process of conversion releases substrates which support bacterial growth. This in turn allows for the bacteria and macro plankton to support even higher trophic levels. This is a form of bottom-up control of aquatic food webs.

Communities

While mycoplankton are found in a variety of aquatic environments, their distribution, abundance, and diversity vary throughout these environments. There is typically a greater amount of diversity and a larger abundance of mycoplankton in coastal waters, due to the extra availability of nutrients. There also exists variation in community composition and diversity at different depths. The control factors for the distribution of mycoplankton is thought to be variable.

References

{{Authority control Aquatic ecology Biological oceanography Planktology Oceanographical terminology