Nanophytoplankton are particularly small

phytoplankton 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 (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

with sizes between 2 and 20 µm. They are the autotrophic part of nanoplankton. Like other phytoplankton, nanophytoplankton are microscopic organisms that obtain energy through the process of photosynthesis and must therefore live in the upper sunlit layer of ocean or other bodies of water. These microscopic free-floating organisms, including

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, fix large amounts of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

which would otherwise be released as

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

. The term nanophytoplankton is derived from the far more widely used term nannoplankton/nanoplankton.

Ecosystem role

Phytoplankton form the beginning of the food chain for aquatic animals.

Zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and krill feed on nanophytoplankton, and are then eaten by whales, seals, birds, fish, squid, and other organisms.

Life cycle

Populations are low in the winter, when nutrients are high, and then the populations increase as the nanophytoplankton consume nearly all of the nutrients, reach their

carrying capacity The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as t ...

, and decline in number at the end of the summer, beginning the cycle again in the winter. However, nanophytoplankton have different seasonal cycles depending on which oceanic biome of the world they live in.Stonehouse, B. ''Polar Ecology''. New York: Chapman and Hall, 1989.

Nutrient uptake

Phytoplanktons' density (1.02 g/cm³) is higher than that of sea water (1.00 g/cm³). Therefore, they sink in the ocean, unless there is an upward movement of water. However, nanophytoplankton, with as small as a 1 µm radius, can swim in the ocean, but at a very slow rate, like "a human swimming in molasses". In either case, movement of water past the organism is created, allowing it to grab nutrients passing by. To supply nutrients through their boundary layer, nanophytoplankton employ diffusion more effectively than swimming, however.

In Antarctic

In the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

in the Antarctic zone, nanophytoplankton are the most abundant type of plankton in terms of number, but not volume. Antarctic marine flora consists almost entirely of algae, with phytoplankton (and, therefore, nanophytoplankton as the most numerous type) having great importance. Nanophytoplankton growth has been seen in pack-ice, covering nearly 73% of the Southern Ocean by the end of the winter. They even grow on icebergs. Nanophytoplankton production is affected by light intensity and duration, ice, surface water stability, and currents. Also, availability of silicates, a nutrient for the organism, can affect photosynthetic efficiency and cell composition. Nanophytoplankton also require vitamins. They thrive in areas of shallow water where there is upwelling and mixing. Although optimal growth for the species occurs in water , growth still occurs in Antarctic waters, which can reach as low as . Limitation of light intensity and duration is another factor for survival. In Antarctica, the sun's lower position above the horizon reduces light due to increased reflection, and the stormy seas reduce transmission of light due to bubble formation. However, some Antarctic nanophytoplankton seem to be adapted to low light levels. Most phytoplankton exist in warmer, equatorial waters. For example, in the northwestern

Philippine Sea The Philippine Sea is a marginal sea of the Western Pacific Ocean east of the Philippine archipelago (hence the name), the largest in the world, occupying an estimated surface area of . The Philippine Sea Plate forms the floor of the sea. Its ...

, the average number of nanophytoplankton was 1x10⁴/l. Nanophytoplankton in particular seem to survive better under the conditions provided by the oceans of the Antarctic. A physiological change in the cells must have occurred to allow this phenomenon. Low

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

is desirable for survival, as well.

Effect on global warming

Continued

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

will significantly alter the food chain on Earth. With nanophytoplankton and phytoplankton at the base of the food chain, their decreased productivity from increased

UV-B Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

radiation from ozone depletion will provide less food for krill and subsequent organisms in the food chain. Antarctica has experienced up to 50%

ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone l ...

, harming nanophytoplankton located here the most. Through carbon fixation, nanophytoplankton absorb carbon from the atmosphere, and with depleting populations, more carbon is left in the air, contributing to more global warming and ozone depletion. The cycle then continues. However, some scientists believe that existence of nanophytoplankton contributes to further progression of global warming, because they absorb the sun's radiation that would otherwise be reflected back into space. Despite the controversy, it is evident that nanophytoplankton, despite their minimal size and apparent irrelevance because they are hardly visible, are an integral part of sustaining life on Earth.

References

External links

*http://sherpaguides.com/georgia/barrier_islands/images/Phytoplankton.gif *http://www.visindavefur.hi.is/myndir/phytoplankton_070305.jpg {{Use dmy dates, date=September 2019 Planktology