Coccolithophores (also called
coccolithophorids) are single-celled
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
,
protistProtists , are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy...
s and
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
belonging to the division
haptophyteThe haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a phylum of algae.The term "Haptophyceae" is sometimes used. This ending implies classification at a lower level...
s. They are distinguished by special
calcium carbonateCalcium carbonate is a chemical compound with the chemical formula CaCO
3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural...
plates (or scales) of uncertain function called
coccolithCoccoliths are individual plates of calcium carbonate formed by coccolithophores which are arranged around them in a coccosphere.- Formation and composition :...
s (calcareous nanoplankton), which are important
microfossilsMicropaleontology is that branch of paleontology which studies microfossils. Microfossils are fossils generally not larger than four millimeters, and commonly smaller than one millimeter, the study of which requires the use of light or electron microscopy...
. Coccolithophores are almost exclusively marine and are found in large numbers throughout the surface
euphotic zoneThe photic zone or euphotic zone is the depth of the water in a lake or ocean, that is exposed to sufficient sunlight for photosynthesis to occur...
of the
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
. An example of a globally-significant coccolithophore is
Emiliania huxleyiEmiliania huxleyi, often abbreviated to simply "EHUX", is a species of coccolithophore with a global distribution from the tropics to subarctic waters. It is studied for the extensive blooms it forms in nutrient depleted waters after the reformation of the summer thermocline. Like other...
.
The arrangement of coccolithophores are as spherical cells about 15-100 micrometres across, enclosed by calcareous plates, coccoliths, about 2-25 micrometres across. Coccolithophores that are alive today have two brown
pigmentA pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
chloroplasts in their cell with the nucleus located between them. The pigments are home to the chlorophyll which carry out
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
. In order to obtain the sunlight needed for photosynthesis, coccolithophores live near the surface of the ocean. Although they have the capability to swim, coccolithophores dominant mode of transport is drifting with ocean current and circulation patterns. However, they may maneuver individually to remain in the euphotic zone during times of extremely favorable conditions.
Due to their
microscopicMicroscopy is the technical field of using microscopes to view samples or objects. There are three well-known branches of microscopy, optical, electron and scanning probe microscopy....
size and the broad distribution of many of their taxa,
coccoliths have become very important as
index fossilIndex fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
s for solving various
stratigraphicStratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
problems. Microfossils are sensitive indicators of changes in the temperature and
salinitySalinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
of the ocean and
seaA sea is any large amount of water filled with animals such as crabs, whales, sharks, and fish, but there is inconsistency as to its precise definition and application. Most commonly, a sea may refer to a large expanse of saline water connected with an ocean, but it is also used sometimes for a...
surface water. The quantitative analysis of
calcareousCalcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 470°C, and vaterite is even less stable....
nanoplankton assemblages is being employed to reveal such changes. They also produce alkenones, biomarkers of great utility in reconstructing ancient temperatures.
Coccolithophores have long been thought to respond to increased ocean acidity, caused by increasing levels, by becoming less calcified. Scientists were recently surprised to learn that in fact the opposite can happen in at least some circumstances, with the model species
E. huxleyiEmiliania huxleyi, often abbreviated to simply "EHUX", is a species of coccolithophore with a global distribution from the tropics to subarctic waters. It is studied for the extensive blooms it forms in nutrient depleted waters after the reformation of the summer thermocline. Like other...
becoming 40% heavier and more abundant in waters of higher CO2 concentration.
See also
- CLAW hypothesis
The CLAW hypothesis proposes a feedback loop that operates between ocean ecosystems and the Earth's climate. The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative...
- Emiliania huxleyi virus 86
Coccolithovirus is a giant double-stranded DNA virus that infects Emiliania huxleyi, a species of coccolithophore. Its genome is 407,339 base pairs long with a G+C content of 41.1%, and contains 472 predicted coding sequences....
- Ocean acidification
Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere...
- Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
- Pleurochrysis carterae
Pleurochrysis carterae is a unicellular coccolithophorid alga that has the ability to calcify subcellularly. They produce calcified scales, known as coccoliths, which are deposited on the surface of the cell resulting in the formation of a coccosphere...
External links