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Mycoplankton are saprotrophic members of the plankton communities of marine and freshwater ecosystems. [1] [2] They are composed of filamentous free-living fungi and yeasts that are associated with planktonic particles or phytoplankton. [3] Similar to bacterioplankton, these aquatic fungi play a significant role in heterotrophic mineralization and nutrient cycling. [4] Mycoplankton can be up to 20 mm in diameter and over 50 mm in length. [5]
In a typical milliliter of seawater, there are approximately 103 to 104 fungal cells. [6] This number is greater in coastal ecosystems and estuaries due to nutritional runoff from terrestrial communities. Aquatic fungi are found in a myriad of ecosystems, from mangroves, to wetlands, to the open ocean. [7] 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. [8] [9] Furthermore, this difference in distribution may vary between seasons due to nutrient availability. [10] Aquatic fungi survive in a constant oxygen deficient environment, and therefore depend on oxygen diffusion by turbulence and oxygen generated by photosynthetic organisms. [11]
There is a large amount of diversity among aquatic fungi. These fungi may be classified using three groups: [11]
The majority of mycoplankton species are higher fungi, found in the Ascomycota and Basidiomycota phyla. [8]
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. [7]
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). [2] The methods and pathways of terrestrial fungi's adaption to the marine environment are still under study.
There are multiple biogeochemical cycles in the Earth's oceans in which Mycoplankton play a role. [12] They are a part of the microbial loop and other forms of nutrient cycling, including the mycoplankton specific mycoflux and mycoloop. [13]
Mycoplankton, like all fungi, play an essential roll in the degradation of detritus and organic matter from plants, as well as other larger organisms. [14] [15] By working with other microbial communities, mycoplankton efficiently convert particulate organic matter to dissolved organic matter as part of biogeochemical cycling. [12] Mycoplankton and heterotrophic bacteria mediate carbon, nitrogen, oxygen, and other nutrient fluxes in marine ecosystems. [16] The incorporation of dissolved organic carbon into microbe biomass is what is known as the microbial loop. [13]
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. [3] [10]
Mycoplankton are important in controlling phytoplankton and zooplankton 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 levels. 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). [13]
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. [13]
Another process which mycoplankton take part in is known as the benthic shunt. This process takes place in the benthic zone, 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. [13]
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. [8] 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. [7] 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.
While mycoplankton are found in a variety of aquatic environments, their distribution, abundance, and diversity vary throughout these environments. [7] 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. [8]
Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish, and baleen whales.
Phytoplankton are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words φυτόν, meaning 'plant', and πλαγκτός, meaning 'wanderer' or 'drifter'.
Zooplankton are the animal component of the planktonic community. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments. In other words, it is a biologically mediated process which results in the sequestering of carbon in the deep ocean away from the atmosphere and the land. The biological pump is the biological component of the "marine carbon pump" which contains both a physical and biological component. It is the part of the broader oceanic carbon cycle responsible for the cycling of organic matter formed mainly by phytoplankton during photosynthesis (soft-tissue pump), as well as the cycling of calcium carbonate (CaCO3) formed into shells by certain organisms such as plankton and mollusks (carbonate pump).
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems, which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two ecosystems are examples of freshwater ecosystems.
Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs:
The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of phosphine gas occurs in only specialized, local conditions. Therefore, the phosphorus cycle should be viewed from whole Earth system and then specifically focused on the cycle in terrestrial and aquatic systems.
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below, which is referred to as the biological pump. Export production is the amount of organic matter produced in the ocean by primary production that is not recycled (remineralised) before it sinks into the aphotic zone. Because of the role of export production in the ocean's biological pump, it is typically measured in units of carbon. The term was coined by explorer William Beebe as observed from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms that live very deep in the water column.
Bacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word πλανκτος, meaning "wanderer" or "drifter", and bacterium, a Latin term coined in the 19th century by Christian Gottfried Ehrenberg. They are found in both seawater and freshwater.
The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere caused by the Coriolis Effect. They generally form in large open ocean areas that lie between land masses.
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 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.
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and in the past billion years; basking sharks and copepods are just two examples of giant and microscopic organisms that feed upon plankton. Planktivory can be an important mechanism of top-down control that contributes to trophic cascades in aquatic and marine systems. There is a tremendous diversity of feeding strategies and behaviors that planktivores utilize to capture prey. Some planktivores utilize tides and currents to migrate between estuaries and coastal waters; other aquatic planktivores reside in lakes or reservoirs where diverse assemblages of plankton are present, or migrate vertically in the water column searching for prey. Planktivore populations can impact the abundance and community composition of planktonic species through their predation pressure, and planktivore migrations facilitate nutrient transport between benthic and pelagic habitats.
Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 millimeters (53 μm) to 2 millimeters.
The viral shunt is a mechanism that prevents marine microbial particulate organic matter (POM) from migrating up trophic levels by recycling them into dissolved organic matter (DOM), which can be readily taken up by microorganisms. The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.
Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, many significant terrestrial primary producers, such as mature forests, grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.
Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly single-celled and microscopic. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics because they are paraphyletic.