Mycoplankton

Marine Ascomycete fungus

Mycoplankton are saprotropic members of the plankton communities of marine and freshwater ecosystems. They are composed of filamentous free-living fungi and yeasts that are associated with planktonic particles or phytoplankton. Similar to bacterioplankton, these aquatic fungi play a significant role in heterotrophic mineralization and nutrient cycling. 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 due to nutritional runoff from terrestrial communities. 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 phytoplankton. 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 and oxygen generated by photosynthetic organisms.

Aquatic fungi can be classified using three groups:

• Lower fungi - adapted to marine habitats (zoosporic fungi, including mastigomycetes: oomycetes & chytridiomycetes)
• Higher fungi -filamentous, modified to planktonic lifestyle (hyphomycetes, ascomycetes, basidiomycetes)
• Terrestrial fungi - contain appendages of marine fungi (trichomycetes)

The majority of mycoplankton species are higher fungi, found in the Ascomycota and Basidiomycota phylums.

According to fossil records, fungi date back to the late Proterozoic era, 900-570 million years ago. It is hypothesized that mycoplankton evolved from terrestrial fungi, likely in the Paleozoic era (390 million years ago). The methods and pathways of terrestrial fungi's adaption to the marine environment are still under study.

Biogeochemical Contributions

The primary role of all fungi is to degrade detrital organic matter from plants, and mycoplankton is no exception. By working with microbial communities, mycoplankton efficiently converts particulate organic matter to dissolved organic matter as part of the biogeochemical cycle. Mycoplankton and heterotrophic bacteria mediate carbon, nitrogen, oxygen, and other nutrient fluxes in marine ecosystems. It has been shown that there are higher concentrations of mycoplankton near the surface and in shallow waters, which indicates their connection with the upwelling of organic matter. This further correlates with abundant phytoplankton communities at the surface, implying that mycoplankton is intimately involved in organic matter consumption in the euphotic zone.

See also

• Algae
• Bacterioplankton
• Biological pump
• Fungus
• Phytoplankton
• Zooplankton