Antarctica is one of the most physically and chemically extreme terrestrial environments to be inhabited by lifeforms. [1] The largest plants are mosses, and the largest animals that do not leave the continent are a few species of insects.
Although most of the continent is covered by glacial ice sheets, ice-free areas comprising approximately 0.4% of the continental land mass are discontinuously distributed around the coastal margins. [1] The McMurdo Dry Valleys region of Antarctica is a polar desert characterized by extremely low annual precipitation (<100 mm (3.9 in)) and an absence of vascular plants and vertebrates; microbial activity dominates biological functioning. [2] Mean summer high and winter low temperatures in the dry valleys are −5 °C (23 °F) and −30 °C (−22 °F). [2] Because precipitation is both infrequent and low, seasonal water availability in hydrologically connected soils make areas adjacent to water bodies more hospitable relative to dry upland soils. [2] Polar ecosystems are particularly sensitive to climate change, where small changes in temperature result in greater changes in local hydrology, dramatically affecting ecosystem processes. [3]
Soils in Antarctica are nearly two-dimensional habitats, with most biological activity limited to the top four or five inches by the permanently frozen ground below. [4] Environments can be limiting due to soil properties such as unfavorable mineralogy, texture, structure, salts, pH, or moisture relationships. [5] Visible sources of organic matter are absent for most of continental Antarctica. [3] Dry Valley soil ecosystems are characterized by large variations in temperature and light regimes, steep chemical gradients and a high incidence of solar radiation with an elevated ultraviolet B (UVB) light component. [1] Dry Valley soils originate from weathering of bedrock and glacial tills that consist of granites, sandstones, basalts and metamorphic rocks. [1] Space within these rocks provide protection for microorganisms against some (but not all) of these conditions: i.e., protection from wind scouring and surface mobility, a reduction in UV exposure, reduced desiccation and enhanced water availability, and thermal buffering. [6] Half of the soils in the Dry Valleys have subsurface ice, either as buried massive ice or as ice-cemented soil (permafrost). [1] The permafrost layer is typically within 30 cm (12 in) of the soil surface. [1]
The harsh environment and low availability of carbon and water support a simplified community of mosses, lichens, and mats of green algae and red, orange, and black cyanobacteria near lakes and ephemeral streams. [4] Living among the mats are bacteria, yeasts, molds, and an array of microscopic invertebrates that feed on microbes, algae, and detritus: nematodes, protozoa, rotifers, tardigrades, and occasionally, mites and springtails. [4] Even simpler communities exist in the arid soils that occupy the majority of the landscape. [3]
Microbes in Antarctica adapt to aridity the same way microbes in hot deserts do: when water becomes scarce, the organisms simply dry up, shut down metabolic activity, and wait in a cryptobiotic state until water again becomes available. [4] Microbes can also go dormant in a cryptobiotic state known as anhydrobiosis when they become dehydrated due to low water availability. [4] A more extreme survival method would be long term natural cryopreservation. Samples of permafrost sediments aged 5–10 thousand to 2–3 million years old have been found to contain viable micromycete and bacterial cells. [7]
Algae is present in almost all ice-free areas and occurs in soils, as epiphytes on mosses, in cyanobacterial mats and in plankton of lakes and ponds. [8] It is also possible to find algae associated with rocks or living in the thin film of melted water in the snow patches. [8] Presently there are over 300 algal taxa identified on Antarctica, with Bacillariophyceae (Diatoms) and Chlorophyta (Green algae) being the most widespread on Antarctica. [8] Diatoms are abundant in aquatic environments decreasing in number in terrestrial habitats. [8] Chlorophyta are also important in mats in lakes and ponds but tend to increase their relative importance in terrestrial environments and especially in soils, where they are the densest algal group. [8] Xanthophyceae (Yellow-green algae) are an important component of the flora in soils of Antarctica. [8] Other algal groups (Dinophyta, Cryptophyta, and Euglenophyta) are mainly limited to freshwater communities of the Dry Valleys. [8]
Distribution of arthropods is limited to areas of high soil moisture and/or access to water, such as streams, or snow meltwater. [8]
Carbon appears to be more important than moisture in defining good habitats for nematodes in the Dry Valleys of Antarctica. [4] Scottnema lindsayae , a microbial feeder and the most abundant and widely distributed metazoan invertebrate, often occurs as the sole metazoan species in the McMurdo Dry Valleys. [3] It makes its living eating bacteria and yeast out in the dry, salty soils that dominate the valleys. [4] All other invertebrate species are more abundant in moist or saturated soils where algae and moss are more abundant. [3] Distribution of most nematode species is correlated negatively with elevation (due to temperature and precipitation) and salinity, and positively with soil moisture, soil organic matter, and nutrient availability. [3] Eudorylaimus spp. is the second most abundant nematode, followed by Plectus murrayi who are the least abundant nematodes. [3] Plectus antarcticus eats bacteria and prefers living in ephemeral streams. [4] An average 2-pound bag of dry valley soils contains approximately 700 nematodes, while the more fertile soil found at higher latitudes on the continent may contain approximately 4,000 nematodes. [4]
Nematode species identified in recent research: [3] [4] [8]
The three species listed below were found in moss-dominated moist soils. [8]
Rotifer species identified in recent research: [8]
Tardigrade species identified in recent research: [8]
Typically, the highest numbers of cultured bacteria are from relatively moist coastal soils, compared with the small bacteria communities of dry inland soils. [8] Cyanobacteria are found in all types of aquatic habitats and often dominate the microbial biomass of streams and lake sediments. [8] Leptolyngbya frigida is dominant in benthic mats, and is frequently found in soils and as an epiphyte on mosses. [8] Nostoc commune can develop to sizes visible to the naked eye if supplied with a thin water film. [8] The genus Gloeocapsa is one of the few cryptoendolithic taxa with a high adaptation to extreme environmental conditions in rocks of the Dry Valleys. [8] Actinomycetota such as Arthrobacter spp., Brevibacterium spp., and Corynebacterium spp. are prominent in the Dry Valleys. [1] Thermophilic bacteria have been isolated from thermally heated soils near Mt. Melbourne and Mt. Rittman in northern Victoria Land. [8] Bacteria genera found in both air samples and the Antarctic include Staphylococcus , Bacillus , Corynebacterium , Micrococcus , Streptococcus , Neisseria , and Pseudomonas . [7] Bacteria were also found living in the cold and dark in a lake buried a half-mile deep (0.80 km) under the ice in Antarctica. [10] [11] [12]
Bacteria species identified in recent research: [8]
Chaetomium gracile is frequently isolated from geothermally heated soil on Mt. Melbourne in northern Victoria Land. [8] Fungi genera found in both air samples and the Antarctic include Penicillium , Aspergillus , Cladosporium , Alternaria , Aureobasidium , Botryotrichum , Botrytis , Geotrichum , Staphylotrichum , Paecilomyces , and Rhizopus . [7]
Fungi species identified in recent research: [8] [14]
Yeast species identified in recent research: [8]
The small amoebae are of two types. The most abundant are Acanthamoeba and Echinamoeba . [8] The second group consists of monopodal, worm-like amoebae, the subcylindrical Hartmannella and Saccamoeba , and the lingulate Platyamoeba stenopodia Page. [8]
Amoebae species identified in recent research: [8]
Flagellate species identified in recent research: [8]
An endolith or endolithic is an organism that is able to acquire the necessary resources for growth in the inner part of a rock, mineral, coral, animal shells, or in the pores between mineral grains of a rock. Many are extremophiles, living in places long considered inhospitable to life. The distribution, biomass, and diversity of endolith microorganisms are determined by the physical and chemical properties of the rock substrate, including the mineral composition, permeability, the presence of organic compounds, the structure and distribution of pores, water retention capacity, and the pH. Normally, the endoliths colonize the areas within lithic substrates to withstand intense solar radiation, temperature fluctuations, wind, and desiccation. They are of particular interest to astrobiologists, who theorize that endolithic environments on Mars and other planets constitute potential refugia for extraterrestrial microbial communities.
Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C (−4 °F) to 20 °C (68 °F). They are found in places that are permanently cold, such as the polar regions and the deep sea. They can be contrasted with thermophiles, which are organisms that thrive at unusually high temperatures, and mesophiles at intermediate temperatures. Psychrophile is Greek for 'cold-loving', from Ancient Greek ψυχρός (psukhrós) 'cold, frozen'.
The Transantarctic Mountains comprise a mountain range of uplifted rock in Antarctica which extends, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats Land. These mountains divide East Antarctica and West Antarctica. They include a number of separately named mountain groups, which are often again subdivided into smaller ranges.
Lake Fryxell is a frozen lake 4.5 kilometres (2.8 mi) long, between Canada Glacier and Commonwealth Glaciers at the lower end of Taylor Valley in Victoria Land, Antarctica. It was mapped in the early 1900s and named during Operation Deep Freeze in the 1950s. There are several forms of algae living in the waters and a weather station located at the lake.
Polar ecology is the relationship between plants and animals in a polar environment. Polar environments are in the Arctic and Antarctic regions. Arctic regions are in the Northern Hemisphere, and it contains land and the islands that surrounds it. Antarctica is in the Southern Hemisphere and it also contains the land mass, surrounding islands and the ocean. Polar regions also contain the subantarctic and subarctic zone which separate the polar regions from the temperate regions. Antarctica and the Arctic lie in the polar circles. The polar circles are imaginary lines shown on maps to be the areas that receives less sunlight due to less radiation. These areas either receive sunlight or shade 24 hours a day because of the earth's tilt. Plants and animals in the polar regions are able to withstand living in harsh weather conditions but are facing environmental threats that limit their survival.
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density. Oligotrophic environments are those that offer little to sustain life. These environments include deep oceanic sediments, caves, glacial and polar ice, deep subsurface soil, aquifers, ocean waters, and leached soils.
Antarctica is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest continent, being about 40% larger than Europe, and has an area of 14,200,000 km2 (5,500,000 sq mi). Most of Antarctica is covered by the Antarctic ice sheet, with an average thickness of 1.9 km (1.2 mi).
Blood Falls is an outflow of an iron oxide–tainted plume of saltwater, flowing from the tongue of Taylor Glacier onto the ice-covered surface of West Lake Bonney in the Taylor Valley of the McMurdo Dry Valleys in Victoria Land, East Antarctica.
The Guébriant Islands are two islands west of the Antarctic Peninsula, in the northern part of Marguerite Bay, lying 9.3 kilometres (5 nmi) southeast of Cape Alexandra, the southeast cape of Adelaide Island. They were discovered by the fourth French Antarctic Expedition 1908–1910 under Jean-Baptiste Charcot and named by him as "Îlots de Guébriant" after the Reverend Jean Budes de Guébriant, a French Catholic missionary to China.
Lake Burton, also known as Burton Lagoon, is a meromictic and saline lake in the Vestfold Hills of Princess Elizabeth Land in Eastern Antarctica. Princess Elizabeth Land, including the lake, is claimed by Australia as part of the Australian Antarctic Territory. The lake has a surface area of 1.35 km2 (0.52 sq mi), a volume of 9.69 million m3, a maximum depth of 18.3 metres (60 ft) and a mean depth of 7.16 metres (23.5 ft). The lake is named after H. R. Burton, a biologist working in the Vestfold Hills of Antarctica.
Acutuncus is a genus of tardigrades containing a single species, Acutuncus antarcticus. Tardigrades, which are eight-legged micro-animals, are commonly referred to as water bears or moss piglets and are found all over the world in varying extreme habitats. First discovered in 1904 and originally named Hypsibius antarcticus, Acutuncus antarcticus is the most abundant tardigrade species in Antarctica.
Soil microbiology is the study of microorganisms in soil, their functions, and how they affect soil properties. It is believed that between two and four billion years ago, the first ancient bacteria and microorganisms came about on Earth's oceans. These bacteria could fix nitrogen, in time multiplied, and as a result released oxygen into the atmosphere. This led to more advanced microorganisms, which are important because they affect soil structure and fertility. Soil microorganisms can be classified as bacteria, actinomycetes, fungi, algae and protozoa. Each of these groups has characteristics that define them and their functions in soil.
The wildlife of Antarctica are extremophiles, having adapted to the dryness, low temperatures, and high exposure common in Antarctica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.
Temperature change due to climate change in Antarctica is not stable over the whole continent. West Antarctica is warming rapidly, while the inland regions are cooled by the winds in Antarctica. Water in the West Antarctic has warmed by 1 °C since year 1955. Further increase in temperature in water and on land will affect the climate, ice mass and life on the continent and have global implications. Present-day greenhouse gas concentrations are higher than ever according to ice cores from Antarctica, which indicates that warming on this continent is not part of a natural cycle and attributable to anthropogenic climate change.
Cristina Takacs-Vesbach is an American microbial ecologist conducting research on the productivity, diversity, and function of microbial communities living at the two extremes of temperature found on Earth-Antarctica's McMurdo Dry Valleys and Yellowstone National Park's thermal springs.
Microbivory is a feeding behavior consisting of eating microbes practiced by animals of the mesofauna, microfauna and meiofauna.
Scottnema lindsayae is a species of nematode belonging to the family Cephalobidae. First described in 1971, it is endemic to Antarctica and most commonly found in the McMurdo Dry Valleys. S. lindsayae, a microscopic worm, feeds on microbes, including bacteria, yeast, and algae. Adapted to very cold and dry climates, its population may be decreasing as a result of climate change.
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