![Coccolithophores](https://upload.wikimedia.org/wikipedia/commons/e/e3/Coccolithophores.png)
Coccolithophores, or coccolithophorids, are
single celled organisms
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell (biology), cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryoti ...
which are part of the
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 ...
, the
autotrophic
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
(self-feeding) component of the
plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
community. They form a group of about 200 species, and belong either to the kingdom
Protista
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
, according to
Robert Whittaker Robert Whitaker or Whittaker may refer to:
*Robert Whittaker (fighter) (born 1990), Australian mixed martial artist
*Robert Whitaker (equestrian) (born 1983), British showjumper
*Robert Whitaker (author) (active since 1989), American author
*Robert ...
's
Five kingdom classification, or clade
Hacrobia
The cryptomonads-haptophytes assemblage is a proposed monophyletic grouping of unicellular eukaryotes that are not included in the SAR supergroup. Several alternative names have been used for the group, including Hacrobia (derived from "ha-" refe ...
, according to a newer biological classification system. Within the Hacrobia, the coccolithophores are in the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
or
division
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
*Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
Haptophyta
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at t ...
, class
Prymnesiophyceae
Prymnesiophyceae is a haptophyte class. Although it was originally described by Casper in 1972, it did not receive a Latin diagnosis (a requirement for valid publication under the International Code of Botanical Nomenclature
The ''Internatio ...
(or
Coccolithophyceae
Prymnesiophyceae is a haptophyte class. Although it was originally described by Casper in 1972, it did not receive a Latin diagnosis (a requirement for valid publication under the International Code of Botanical Nomenclature
The ''Internatio ...
). Coccolithophores are almost exclusively
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
, are
photosynthetic
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
, and exist in large numbers throughout the
sunlight zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
of the
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
.
Coccolithophores are the most productive
calcifying organism
Marine biogenic calcification is the process by which marine organisms such as oysters and clams form calcium carbonate. Seawater is full of dissolved compounds, ions and nutrients that organisms can use for energy and, in the case of calcificati ...
s on the planet, covering themselves with a
calcium carbonate shell called a ''
coccosphere
Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdo ...
''. However, the reasons they
calcify Hard tissue, refers to "normal" calcified tissue, is the tissue which is mineralized and has a firm intercellular matrix. The hard tissues of humans are bone, tooth enamel, dentin, and cementum. The term is in contrast to soft tissue.
Bone
Bone ...
remains elusive. One key function may be that the coccosphere offers protection against
microzooplankton
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 ...
predation, which is one of the main causes of phytoplankton death in the ocean.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Coccolithophores are ecologically important, and biogeochemically they play significant roles in the marine
biological pump
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.Sigman DM & GH ...
and the
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
They are of particular interest to those studying global
climate change
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 ...
because, as
ocean acidity increases, their coccoliths may become even more important as a
carbon sink
A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide () from the atmosphere.
Globally, the two most important carbon si ...
.
Management strategies are being employed to prevent
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
-related coccolithophore blooms, as these blooms lead to a decrease in nutrient flow to lower levels of the ocean.
The most abundant species of coccolithophore, ''
Emiliania huxleyi
''Emiliania huxleyi'' is a species of coccolithophore found in almost all ocean ecosystems from the equator to sub-polar regions, and from nutrient rich upwelling zones to nutrient poor oligotrophic waters. It is one of thousands of different ...
'', belongs to the order
Isochrysidales
Isochrysidales is an order of Haptophyceae
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used ...
and family
Noëlaerhabdaceae
Noelaerhabdaceae is a family of coccolithophorids. Some genera include: '' Emiliania'' W.W.Hay & H.P.Mohler, '' Gephyrocapsa'' Kamptner, and '' Reticulofenestra'' W.W.Hay, Mohler & M.Wade.
Genus
*'' Reticulofenestra''
*'' Pyrocyclus''
*'' Pseud ...
.
It is found in
temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
,
subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
, and
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
oceans.
This makes ''E. huxleyi'' an important part of the
planktonic
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
base of a large proportion of
marine food webs
Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. Thi ...
. It is also the fastest growing coccolithophore in laboratory cultures.
It is studied for the extensive
blooms it forms in nutrient depleted waters after the reformation of the summer
thermocline
A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more drastically with ...
.
and for its production of molecules known as
alkenone
Alkenones are long-chain unsaturated methyl and ethyl ''n''-ketones produced by a few phytoplankton species of the class Prymnesiophyceae.Marlowe, I.T., Green, J.C., Neal, A.C., Brassell, S.C., Eglinton, G. and Course, P.A. (1984) "Long-chain (''n ...
s that are commonly used by
earth scientists
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface ...
as a means to estimate past
sea surface temperature
Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air mass ...
s.
[.]
Overview
Coccolithophores (or coccolithophorids, from the adjective) form a group of about 200 phytoplankton species. They belong either to the kingdom
Protista
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
, according to
Robert Whittaker Robert Whitaker or Whittaker may refer to:
*Robert Whittaker (fighter) (born 1990), Australian mixed martial artist
*Robert Whitaker (equestrian) (born 1983), British showjumper
*Robert Whitaker (author) (active since 1989), American author
*Robert ...
's
Five kingdom classification, or clade
Hacrobia
The cryptomonads-haptophytes assemblage is a proposed monophyletic grouping of unicellular eukaryotes that are not included in the SAR supergroup. Several alternative names have been used for the group, including Hacrobia (derived from "ha-" refe ...
, according to the newer biological classification system. Within the Hacrobia, the coccolithophores are in the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
or
division
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
*Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
Haptophyta
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at t ...
, class
Prymnesiophyceae
Prymnesiophyceae is a haptophyte class. Although it was originally described by Casper in 1972, it did not receive a Latin diagnosis (a requirement for valid publication under the International Code of Botanical Nomenclature
The ''Internatio ...
(or
Coccolithophyceae
Prymnesiophyceae is a haptophyte class. Although it was originally described by Casper in 1972, it did not receive a Latin diagnosis (a requirement for valid publication under the International Code of Botanical Nomenclature
The ''Internatio ...
).
[.] Coccolithophores are distinguished by special
calcium carbonate plates (or scales) of uncertain function called ''
coccolith
Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as ''Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere''. ...
s'', which are also important
microfossils
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...
. However, there are Prymnesiophyceae species lacking coccoliths (e.g. in genus ''
Prymnesium
''Prymnesium'' is a genus of haptophytes, including the species ''Prymnesium parvum''.
The genus is a unicellular motile alga. It is ellipsoidal in shape one flagellum is straight and there are two longer ones which enable movement.
The name Lat ...
''), so not every member of Prymnesiophyceae is a coccolithophore.
Coccolithophores are single-celled
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 ...
that produce small
calcium carbonate (CaCO
3) scales (
coccolith
Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as ''Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere''. ...
s) which cover the cell surface in the form of a spherical coating, called a
coccosphere
Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdo ...
. They have been an integral part of
marine plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
communities since the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
. Today, coccolithophores contribute ~1–10% to
primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
in the surface ocean and ~50% to pelagic CaCO
3 sediments. Their calcareous shell increases the sinking velocity of photosynthetically fixed into the deep ocean by
ballasting organic matter. At the same time, the
biogenic
A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...
precipitation of calcium carbonate during coccolith formation reduces the total alkalinity of seawater and releases . Thus, coccolithophores play an important role in the
marine carbon cycle
The oceanic carbon cycle (or marine carbon cycle) is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many inter ...
by influencing the efficiency of the
biological carbon pump
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.Sigman DM & GH ...
and the oceanic uptake of atmospheric .
As of 2021, it is not known why coccolithophores calcify and how their ability to produce coccoliths is associated with their ecological success.
The most plausible benefit of having a coccosphere seems to be a protection against predators or viruses.
Viral infection is an important cause of phytoplankton death in the oceans, and it has recently been shown that calcification can influence the interaction between a coccolithophore and its virus. The major predators of marine phytoplankton are
microzooplankton
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 ...
like
ciliate
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...
s and
dinoflagellate
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s. These are estimated to consume about two-thirds of the primary production in the ocean and microzooplankton can exert a strong grazing pressure on coccolithophore populations. Although calcification does not prevent predation, it has been argued that the coccosphere reduces the grazing efficiency by making it more difficult for the predator to utilise the organic content of coccolithophores.
Heterotrophic
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
protist
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
s are able to selectively choose prey on the basis of its size or shape and through chemical signals and may thus favor other prey that is available and not protected by coccoliths.
Structure
![Diagram of a coccolithophore cell and its shield of coccoliths](https://upload.wikimedia.org/wikipedia/commons/2/23/Diagram_of_a_coccolithophore_cell_and_its_shield_of_coccoliths.png)
Coccolithophores are spherical cells about 5–100 micrometres across, enclosed by calcareous plates called
coccoliths
Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as ''Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere''. ...
, which are about 2–25 micrometres across. Each cell contains two brown
chloroplasts
A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, ...
which surround the
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucle ...
.
Enclosed in each coccosphere is a single cell with
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
bound
organelles
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
. Two large
chloroplasts
A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, ...
with brown
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
are located on either side of the cell and surround the
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucle ...
,
mitochondria
A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
,
golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ins ...
,
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
, and other organelles. Each cell also has two
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
r structures, which are involved not only in motility, but also in
mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
and formation of the
cytoskeleton
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...
.
[.] In some species, a functional or
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
haptonema
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at t ...
is also present.
This structure, which is unique to
haptophytes
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...
, coils and uncoils in response to environmental stimuli. Although poorly understood, it has been proposed to be involved in prey capture.
Ecology
Life history strategy
The life cycle of coccolithophores is characterized by an alternation of
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
and
haploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
phases. They alternate from the haploid to diploid phase through
syngamy
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
and from diploid to haploid through
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
. In contrast with most organisms with alternating life cycles, asexual reproduction by mitosis is possible in both phases of the life cycle.
Both
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
and
biotic factors
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
may affect the frequency with which each phase occurs.
Coccolithophores
reproduce asexually
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
through
binary fission. In this process the coccoliths from the parent cell are divided between the two daughter cells. There have been suggestions stating the possible presence of a sexual reproduction process due to the diploid stages of the coccolithophores, but this process has never been observed.
K or r- selected strategies of coccolithophores depend on their life cycle stage. When coccolithophores are diploid, they are r-selected. In this phase they tolerate a wider range of nutrient compositions. When they are haploid they are K- selected and are often more competitive in stable low nutrient environments.
Most coccolithophores are K strategist and are usually found on nutrient-poor surface waters. They are poor competitors when compared to other phytoplankton and thrive in habitats where other phytoplankton would not survive.
These two stages in the life cycle of coccolithophores occur seasonally, where more nutrition is available in warmer seasons and less is available in cooler seasons. This type of life cycle is known as a complex heteromorphic life cycle.
Global distribution
Coccolithophores occur throughout the world's oceans. Their distribution varies vertically by stratified layers in the ocean and geographically by different temporal zones.
[.] While most modern coccolithophores can be located in their associated stratified
oligotrophic
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 ...
conditions, the most abundant areas of coccolithophores where there is the highest species diversity are located in subtropical zones with a temperate climate.
While water temperature and the amount of light intensity entering the water's surface are the more influential factors in determining where species are located, the ocean currents also can determine the location where certain species of coccolithophores are found.
Although motility and colony formation vary according to the life cycle of different coccolithophore species, there is often alternation between a motile, haploid phase, and a non-motile diploid phase. In both phases, the organism's dispersal is largely due to ocean
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
s and circulation patterns.
Within the Pacific Ocean, approximately 90 species have been identified with six separate zones relating to different Pacific currents that contain unique groupings of different species of coccolithophores.
The highest diversity of coccolithophores in the Pacific Ocean was in an area of the ocean considered the Central North Zone which is an area between 30
oN and 5
oN, composed of the North Equatorial Current and the Equatorial Countercurrent. These two currents move in opposite directions, east and west, allowing for a strong mixing of waters and allowing a large variety of species to populate the area.
In the Atlantic Ocean, the most abundant species are ''
E. huxleyi'' and ''Florisphaera profunda'' with smaller concentrations of the species ''Umbellosphaera'' ''irregularis'', ''Umbellosphaera tenuis'' and different species of ''Gephyrocapsa''.
Deep-dwelling coccolithophore species abundance is greatly affected by
nutricline and
thermocline
A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more drastically with ...
depths. These coccolithophores increase in abundance when the nutricline and thermocline are deep and decrease when they are shallow.
The complete distribution of coccolithophores is currently not known and some regions, such as the Indian Ocean, are not as well studied as other locations in the Pacific and Atlantic Oceans. It is also very hard to explain distributions due to multiple constantly changing factors involving the ocean's properties, such as coastal and equatorial
upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
, frontal systems,
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
environments, unique oceanic topography, and pockets of isolated high or low water temperatures.
The upper photic zone is low in nutrient concentration, high in light intensity and penetration, and usually higher in temperature. The lower photic zone is high in nutrient concentration, low in light intensity and penetration and relatively cool. The middle photic zone is an area that contains the same values in between that of the lower and upper photic zones.
Great Calcite Belt
The
Great Calcite Belt of 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 ...
is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental
influences on the distribution of different species within these taxonomic groups.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
The Great Calcite Belt, defined as an elevated
particulate inorganic carbon
Particulate inorganic carbon (PIC) can be contrasted with dissolved inorganic carbon (DIC), the other form of inorganic carbon found in the ocean. These distinctions are important in chemical oceanography. Particulate inorganic carbon is sometim ...
(PIC) feature occurring alongside seasonally elevated
chlorophyll a in
austral spring and summer in the Southern Ocean,
plays an important role in climate fluctuations, accounting for over 60% of the Southern Ocean area (30–60° S).
The region between 30° and 50° S has the highest uptake of anthropogenic carbon dioxide (CO
2) alongside the North Atlantic and North Pacific oceans.
Effect of global climate change on distribution
Recent studies show that climate change has direct and indirect impacts on Coccolithophore distribution and productivity. They will inevitably be affected by the increasing temperatures and thermal stratification of the top layer of the ocean, since these are prime controls on their ecology, although it is not clear whether global warming would result in net increase or decrease of coccolithophores. As they are calcifying organisms, it has been suggested that
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
due to increasing carbon dioxide could severely affect coccolithophores.
Recent increases have seen a sharp increase in the population of coccolithophores.
Role in the food web
![Virus cocco 2](https://upload.wikimedia.org/wikipedia/commons/4/4f/Virus_cocco_2.jpg)
Coccolithophores are one of the more abundant primary producers in the ocean. As such, they are a large contributor to the
primary productivity
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
of the tropical and subtropical oceans, however, exactly how much has yet to have been recorded.
Dependence on nutrients
The ratio between the concentrations of
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
and
silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
in particular areas of the ocean dictates
competitive dominance within phytoplankton communities. Each ratio essentially tips the odds in favor of either
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s or other groups of phytoplankton, such as coccolithophores. A low silicate to nitrogen and phosphorus ratio allows coccolithophores to outcompete other phytoplankton species; however, when silicate to phosphorus to nitrogen ratios are high coccolithophores are outcompeted by diatoms. The increase in agricultural processes lead to
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
of waters and thus, coccolithophore blooms in these high nitrogen and phosphorus, low silicate environments.
Impact on water column productivity
The
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
in calcium carbonate allows coccoliths to scatter more light than they absorb. This has two important consequences: 1) Surface waters become brighter, meaning they have a higher
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
, and 2) there is induced
photoinhibition
Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as ...
, meaning photosythetic production is diminished due to an excess of light. In case 1), a high concentration of coccoliths leads to a simultaneous increase in surface water temperature and decrease in the temperature of deeper waters. This results in more
stratification
Stratification may refer to:
Mathematics
* Stratification (mathematics), any consistent assignment of numbers to predicate symbols
* Data stratification in statistics
Earth sciences
* Stable and unstable stratification
* Stratification, or str ...
in the water column and a decrease in the vertical mixing of nutrients. However, a recent study estimated that the overall effect of coccolithophores on the increased in
radiative forcing
Radiative forcing (or climate forcing) is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change as measured by watts / metre2. It is a scientific concept used to quantify and compare the external ...
of the ocean is less than that from anthropogenic factors.
Therefore, the overall result of large blooms of coccolithophores is a decrease in water column productivity, rather than a contribution to global warming.
Predator-prey interactions
Their predators include the common predators of all phytoplankton including small fish, zooplankton, and shellfish larvae.
Viruses specific to this species have been isolated from several locations worldwide and appear to play a major role in spring bloom dynamics.
=Toxicity
=
No environmental evidence of coccolithophore toxicity has been reported, but they belong to the class Prymnesiophyceae which contain orders with toxic species. Toxic species have been found in the genera ''Prymnesium'' Massart and ''Chrysochromulina'' Lackey. Members of the genus ''Prymnesium'' have been found to produce haemolytic compounds, the agent responsible for toxicity. Some of these toxic species are responsible for large fish kills and can be accumulated in organisms such as shellfish; transferring it through the food chain. In laboratory tests for toxicity members of the oceanic coccolithophore genera ''Emiliania, Gephyrocapsa, Calcidiscus'' and ''Coccolithus'' were shown to be non-toxic as were species of the coastal genus ''Hymenomonas'', however several species of ''Pleurochrysis'' and ''Jomonlithus'', both coastal genera were toxic to ''Artemia''.
Community interactions
Coccolithophorids are predominantly found as single, free-floating haploid or diploid cells.
Competition
Most
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 ...
need sunlight and nutrients from the ocean to survive, so they thrive in areas with large inputs of nutrient rich water upwelling from the lower levels of the ocean. Most coccolithophores require sunlight only for energy production, and have a higher ratio of nitrate uptake over ammonium uptake (nitrogen is required for growth and can be used directly from nitrate but not ammonium). Because of this they thrive in still, nutrient-poor environments where other phytoplankton are starving.
Trade-off
A trade-off (or tradeoff) is a situational decision that involves diminishing or losing one quality, quantity, or property of a set or design in return for gains in other aspects. In simple terms, a tradeoff is where one thing increases, and anot ...
s associated with these faster growth rates include a smaller cell radius and lower cell volume than other types of phytoplankton.
Viral infection and coevolution
Giant
DNA-containing viruses are known to
lytically infect coccolithophores, particularly ''E. huxleyi''. These viruses, known as E. huxleyi viruses (EhVs), appear to infect the coccosphere coated diploid phase of the life cycle almost exclusively. It has been proposed that as the haploid organism is not infected and therefore not affected by the virus, the co-evolutionary "
arms race
An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more states to have superior armed forces; a competition concerning production of weapons, the growth of a military, and t ...
" between coccolithophores and these viruses does not follow the classic
Red Queen evolutionary framework, but instead a "Cheshire Cat" ecological dynamic.
More recent work has suggested that viral synthesis of
sphingolipids
Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extracts in the 1870s and were named after the mythological sphinx because o ...
and induction of
programmed cell death
Programmed cell death (PCD; sometimes referred to as cellular suicide) is the death of a cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usually confers advantage durin ...
provides a more direct link to study a Red Queen-like
coevolution
In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...
ary arms race at least between the coccolithoviruses and diploid organism.
Evolution and diversity
Coccolithophores are members of the clade
Haptophyta
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at t ...
, which is a sister clade to
Centrohelida
The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth.
Characteristics
Individuals are unicellular and spher ...
, which are both in
Haptista
Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with ''Ancoracysta twista'', forms a sister clade to the SAR+Telonemia supergroup, but it may also be sister t ...
.
The oldest known coccolithophores are known from the Late Triassic, around the
Norian
The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic defi ...
-
Rhaetian
The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...
boundary. Diversity steadily increased over the course of the Mesozoic, reaching its apex during the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
. However, there was a sharp drop during the
Cretaceous-Paleogene extinction event, when more than 90% of coccolithophore species became extinct. Coccoliths reached another, lower apex of diversity during the
Paleocene-Eocene thermal maximum, but have subsequently declined since the
Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
due to decreasing global temperatures, with species that produced large and heavily calcified coccoliths most heavily affected.
Coccolithophore shells
* Exoskeleton: coccospheres and coccoliths
Each coccolithophore encloses itself in a protective shell of
coccoliths
Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores (single-celled phytoplankton such as ''Emiliania huxleyi'') and cover the cell surface arranged in the form of a spherical shell, called a ''coccosphere''. ...
, calcified scales which make up its
exoskeleton
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...
or coccosphere.
The coccoliths are created inside the coccolithophore cell and while some species maintain a single layer throughout life only producing new coccoliths as the cell grows, others continually produce and shed coccoliths.
Composition
The primary constituent of coccoliths is calcium carbonate, or
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Chalk ...
. Calcium carbonate is transparent, so the organisms' photosynthetic activity is not compromised by encapsulation in a coccosphere.
Formation
Coccoliths are produced by a
biomineralization
Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon; ...
process known as coccolithogenesis.
Generally, calcification of coccoliths occurs in the presence of light, and these scales are produced much more during the exponential phase of growth than the stationary phase.
Although not yet entirely understood, the biomineralization process is tightly regulated by
calcium signaling
Calcium signaling is the use of calcium ions (Ca2+) to communicate and drive intracellular processes often as a step in signal transduction. Ca2+ is important for cellular signalling, for once it enters the cytosol of the cytoplasm it exerts all ...
.
Calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
formation begins in the
golgi complex
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles insi ...
where protein templates nucleate the formation of CaCO
3 crystals and complex acidic
polysaccharides
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
control the shape and growth of these crystals.
As each scale is produced, it is exported in a Golgi-derived
vesicle
Vesicle may refer to:
; In cellular biology or chemistry
* Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane
* Synaptic vesicle
; In human embryology
* Vesicle (embryology), bulge-like features o ...
and added to the inner surface of the coccosphere. This means that the most recently produced coccoliths may lie beneath older coccoliths.
Depending upon the phytoplankton's stage in the life cycle, two different types of coccoliths may be formed. Holococcoliths are produced only in the haploid phase, lack radial symmetry, and are composed of anywhere from hundreds to thousands of similar minute (ca 0.1 μm) rhombic
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
crystals. These crystals are thought to form at least partially outside the cell. Heterococcoliths occur only in the diploid phase, have radial symmetry, and are composed of relatively few complex crystal units (fewer than 100). Although they are rare, combination coccospheres, which contain both holococcoliths and heterococcoliths, have been observed in the plankton recording coccolithophore life cycle transitions. Finally, the coccospheres of some species are highly modified with various appendages made of specialized coccoliths.
Function
While the exact function of the coccosphere is unclear, many potential functions have been proposed. Most obviously coccoliths may protect the phytoplankton from predators. It also appears that it helps them to create a more stable
pH. During photosynthesis carbon dioxide is removed from the water, making it more basic. Also calcification removes carbon dioxide, but chemistry behind it leads to the opposite pH reaction; it makes the water more acidic. The combination of photosynthesis and calcification therefore even out each other regarding pH changes. In addition, these exoskeletons may confer an advantage in energy production, as coccolithogenesis seems highly coupled with photosynthesis. Organic precipitation of calcium carbonate from bicarbonate solution produces free carbon dioxide directly within the cellular body of the alga, this additional source of gas is then available to the Coccolithophore for photosynthesis. It has been suggested that they may provide a cell-wall like barrier to isolate intracellular chemistry from the marine environment.
More specific, defensive properties of coccoliths may include protection from osmotic changes, chemical or mechanical shock, and short-wavelength light.
It has also been proposed that the added weight of multiple layers of coccoliths allows the organism to sink to lower, more nutrient rich layers of the water and conversely, that coccoliths add buoyancy, stopping the cell from sinking to dangerous depths.
Coccolith appendages have also been proposed to serve several functions, such as inhibiting grazing by zooplankton.
Uses
Coccoliths are the main component of
the Chalk, a Late Cretaceous rock formation which outcrops widely in southern England and forms the
White Cliffs of Dover
The White Cliffs of Dover is the region of English coastline facing the Strait of Dover and France. The cliff face, which reaches a height of , owes its striking appearance to its composition of chalk accented by streaks of black flint, deposi ...
, and of other similar rocks in many other parts of the world.
At the present day sedimented coccoliths are a major component of the
calcareous oozes that cover up to 35% of the ocean floor and is kilometres thick in places.
Because of their abundance and wide geographic ranges, the coccoliths which make up the layers of this ooze and the chalky sediment formed as it is compacted serve as valuable
microfossils
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...
.
Calcification
Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...
, the biological production of
calcium carbonate (CaCO
3), is a key process in the
marine carbon cycle
The oceanic carbon cycle (or marine carbon cycle) is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many inter ...
. Coccolithophores are the major planktonic group responsible for pelagic CaCO
3 production. The diagram on the right shows the energetic costs of coccolithophore calcification:
: (A) Transport processes include the transport into the cell from the surrounding seawater of primary calcification substrates
Ca2+ and
HCO3− (black arrows) and the removal of the end product H+ from the cell (gray arrow). The transport of Ca
2+ through the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...
to the CV is the dominant cost associated with calcification.
: (B)
Metabolic process
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
es include the synthesis of CAPs (gray rectangles) by the
Golgi complex
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles insi ...
(white rectangles) that regulate the
nucleation
In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that deter ...
and geometry of CaCO
3 crystals. The completed coccolith (gray plate) is a complex structure of intricately arranged CAPs and CaCO
3 crystals.
: (C) Mechanical and structural processes account for the secretion of the completed coccoliths that are transported from their original position adjacent to the nucleus to the cell periphery, where they are transferred to the surface of the cell. The costs associated with these processes are likely to be comparable to organic-scale
exocytosis
Exocytosis () is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell ('' exo-'' + ''cytosis''). As an active transport mechanism, exocytosis requires the use o ...
in noncalcifying
haptophyte
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for ''Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at t ...
algae.
The diagram on the left shows the benefits of coccolithophore calcification. (A) Accelerated photosynthesis includes CCM (1) and enhanced light uptake via scattering of scarce photons for deep-dwelling species (2). (B) Protection from photodamage includes sunshade protection from ultraviolet (UV) light and photosynthetic active radiation (PAR) (1) and energy dissipation under high-light conditions (2). (C) Armor protection includes protection against viral/bacterial infections (1) and grazing by selective (2) and nonselective (3) grazers.
The degree by which calcification can adapt to
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
is presently unknown. Cell physiological examinations found the essential
H+ efflux (stemming from the use of HCO
3− for intra-cellular calcification) to become more costly with ongoing ocean acidification as the electrochemical H+ inside-out gradient is reduced and passive proton outflow impeded.
Adapted cells would have to activate
proton channel
A proton pump is an integral membrane protein pump that builds up a proton gradient across a biological membrane. Proton pumps catalyze the following reaction:
: n one side of a biological membrane/sub> + energy n the other side of the membr ...
s more frequently, adjust their
membrane potential
Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...
, and/or lower their internal
pH. Reduced intra-cellular pH would severely affect the entire cellular machinery and require other processes (e.g.
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
) to co-adapt in order to keep H+ efflux alive. The obligatory H+ efflux associated with calcification may therefore pose a fundamental constraint on adaptation which may potentially explain why "calcification crisis" were possible during long-lasting (thousands of years) CO
2 perturbation events
even though evolutionary adaption to changing
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
chemistry conditions is possible within one year.
Unraveling these fundamental constraints and the limits of adaptation should be a focus in future coccolithophore studies because knowing them is the key information required to understand to what extent the calcification response to carbonate chemistry perturbations can be compensated by evolution.
Silicate- or cellulose-armored functional groups such as
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s and
dinoflagellate
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s do not need to sustain the calcification-related H+ efflux. Thus, they probably do not need to adapt in order to keep costs for the production of structural elements low. On the contrary, dinoflagellates (except for calcifying species; with generally inefficient CO
2-fixing
RuBisCO enzymes may even profit from chemical changes since photosynthetic
carbon fixation
Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon (particularly in the form of carbon dioxide) is converted to organic compounds by living organisms. The compounds are then used to store energy and as ...
as their source of structural elements in the form of cellulose should be facilitated by the ocean acidification-associated CO
2 fertilization. Under the assumption that any form of shell/exoskeleton protects phytoplankton against predation
non-calcareous armors may be the preferable solution to realize protection in a future ocean.
![Energetic effort for armor construction in shell-forming phytoplankton](https://upload.wikimedia.org/wikipedia/commons/7/74/Energetic_effort_for_armor_construction_in_shell-forming_phytoplankton.jpg)
The diagram on the right is a representation of how the comparative energetic effort for armor construction in diatoms, dinoflagellates and coccolithophores appear to operate. The
frustule
A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica, made from silicic acid, and is coated with a layer of organic substance, which was referred to in the early literature on d ...
(diatom shell) seems to be the most inexpensive armor under all circumstances because diatoms typically outcompete all other groups when silicate is available. The coccosphere is relatively inexpensive under sufficient
2">O2 high
3−">CO3− and low
+because the substrate is saturating and protons are easily released into seawater.
In contrast, the construction of
thecal elements, which are organic (
cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
) plates that constitute the dinoflagellate shell, should rather be favored at high H+ concentrations because these usually coincide with high
2">O2 Under these conditions dinoflagellates could down-regulate the energy-consuming operation of carbon concentrating mechanisms to fuel the production of organic source material for their shell. Therefore, a shift in carbonate chemistry conditions toward high
2">O2may promote their competitiveness relative to coccolithophores. However, such a hypothetical gain in competitiveness due to altered carbonate chemistry conditions would not automatically lead to dinoflagellate dominance because a huge number of factors other than carbonate chemistry have an influence on species composition as well.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
*
Defence against predation
Currently, the evidence supporting or refuting a protective function of the coccosphere against predation is limited. Some researchers found that overall microzooplankton predation rates were reduced during blooms of the coccolithophore ''
Emiliania huxleyi
''Emiliania huxleyi'' is a species of coccolithophore found in almost all ocean ecosystems from the equator to sub-polar regions, and from nutrient rich upwelling zones to nutrient poor oligotrophic waters. It is one of thousands of different ...
'', while others found high microzooplankton grazing rates on natural coccolithophore communities. In 2020, researchers found that ''in situ'' ingestion rates of microzooplankton on ''E. huxleyi'' did not differ significantly from those on similar sized non-calcifying phytoplankton. In laboratory experiments the heterotrophic dinoflagellate ''
Oxyrrhis marina
''Oxyrrhis marina'' is a species of dinoflagellates with flagella. A marine heterotroph, it is found in much of the world.
Description
This protozoan species has an asymmetrical oval shape to its single-celled body.Lowe, C. D., et al. (2011)W ...
'' preferred calcified over non-calcified cells of ''E. huxleyi'', which was hypothesised to be due to size selective feeding behaviour, since calcified cells are larger than non-calcified ''E. huxleyi''. In 2015, Harvey et al. investigated predation by the dinoflagellate ''O. marina'' on different genotypes of non-calcifying ''E. huxleyi'' as well as calcified strains that differed in the degree of calcification.
They found that the ingestion rate of ''O. marina'' was dependent on the genotype of ''E. huxleyi'' that was offered, rather than on their degree of calcification. In the same study, however, the authors found that predators which preyed on non-calcifying
genotype
The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
s grew faster than those fed with calcified cells.
In 2018, Strom et al. compared predation rates of the dinoflagellate ''
Amphidinium longum'' on calcified relative to naked ''E. huxleyi'' prey and found no evidence that the coccosphere prevents ingestion by the grazer.
Instead, ingestion rates were dependent on the offered genotype of E. huxleyi.
Altogether, these two studies suggest that the genotype has a strong influence on ingestion by the microzooplankton species, but if and how calcification protects coccolithophores from microzooplankton predation could not be fully clarified.
Importance in global climate change
Impact on the carbon cycle
Coccolithophores have both long and short term effects on the
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
. The production of coccoliths requires the uptake of
dissolved inorganic carbon
Dissolved inorganic carbon (DIC) is the sum of the aqueous species of inorganic carbon in a solution. Carbon compounds can be distinguished as either organic or inorganic, and as dissolved or particulate, depending on their composition. Organic c ...
and calcium.
Calcium carbonate and
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 ...
are produced from calcium and
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochemic ...
by the following chemical reaction:
:Ca
2+ + 2HCO
3− CaCO
3 + CO
2 + H
2O.
Because coccolithophores are photosynthetic organisms, they are able to use some of the CO
2 released in the calcification reaction for
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
.
However, the production of calcium carbonate drives surface alkalinity down, and in conditions of low alkalinity the CO
2 is instead released back into the atmosphere.
As a result of this, researchers have postulated that large blooms of coccolithophores may contribute to global warming in the short term.
A more widely accepted idea, however, is that over the long term coccolithophores contribute to an overall decrease in atmospheric CO
2 concentrations. During calcification two carbon atoms are taken up and one of them becomes trapped as calcium carbonate. This calcium carbonate sinks to the bottom of the ocean in the form of coccoliths and becomes part of sediment; thus, coccolithophores provide a sink for emitted carbon, mediating the effects of greenhouse gas emissions.
Evolutionary responses to ocean acidification
Research also suggests that
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
due to increasing concentrations of CO
2 in the atmosphere may affect the calcification machinery of coccolithophores. This may not only affect immediate events such as increases in population or coccolith production, but also may induce
evolutionary adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...
of coccolithophore species over longer periods of time. For example, coccolithophores use H
+ ion channels
Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...
in to constantly pump H
+ ions out of the cell during coccolith production. This allows them to avoid
acidosis
Acidosis is a process causing increased acidity in the blood and other body tissues (i.e., an increase in hydrogen ion concentration). If not further qualified, it usually refers to acidity of the blood plasma.
The term ''acidemia'' describes t ...
, as coccolith production would otherwise produce a toxic excess of H
+ ions. When the function of these ion channels is disrupted, the coccolithophores stop the calcification process to avoid acidosis, thus forming a
feedback loop
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled c ...
.
Low ocean
alkalinity
Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale.
Alkalinity is the strength of ...
, impairs ion channel function and therefore places evolutionary selective pressure on coccolithophores and makes them (and other ocean calcifiers) vulnerable to ocean acidification.
In 2008, field evidence indicating an increase in calcification of newly formed ocean sediments containing coccolithophores bolstered the first ever experimental data showing that an increase in ocean CO
2 concentration results in an increase in calcification of these organisms.
Decreasing coccolith mass is related to both the increasing concentrations of CO
2 and decreasing concentrations of CO
32– in the world's oceans. This lower calcification is assumed to put coccolithophores at ecological disadvantage. Some species like ''Calcidiscus'' ''leptoporus'', however, are not affected in this way, while the most abundant coccolithophore species, ''E. huxleyi'' might be (study results are mixed).
Also, highly calcified coccolithophorids have been found in conditions of low CaCO
3 saturation contrary to predictions.
Understanding the effects of increasing ocean acidification on coccolithophore species is absolutely essential to predicting the future chemical composition of the ocean, particularly its carbonate chemistry. Viable conservation and management measures will come from future research in this area. Groups like the European-based
CALMARO are monitoring the responses of coccolithophore populations to varying pH's and working to determine environmentally sound measures of control.
File:Gephyrocapsa oceanica.jpg, ''Gephyrocapsa oceanica
''Gephyrocapsa oceanica'' is a species of coccolithophorid. It is the type species of the genus ''Gephyrocapsa''. The species is an important Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (g ...
''
Scale bar = 1.0 μm
File:Diversity of coccolithophores (cropped) (Rhabdosphaera clavigera).jpg, '' Rhabdosphaera clavigera''
File:Diversity of coccolithophores (cropped).(Discosphaera tubifera).jpg, '' Discosphaera tubifera''
Impact on microfossil record
Coccolith fossils are prominent and valuable
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an adje ...
microfossil
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...
s. They are the largest global source of biogenic calcium carbonate, and significantly contribute to the global
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
. They are the main constituent of chalk deposits such as the
white cliffs of Dover
The White Cliffs of Dover is the region of English coastline facing the Strait of Dover and France. The cliff face, which reaches a height of , owes its striking appearance to its composition of chalk accented by streaks of black flint, deposi ...
.
Of particular interest are fossils dating back to the
Palaeocene-Eocene Thermal Maximum 55 million years ago. This period is thought to correspond most directly to the current levels of CO
2 in the ocean.
Finally, field evidence of coccolithophore fossils in rock were used to show that the deep-sea fossil record bears a
rock record bias similar to the one that is widely accepted to affect the land-based
fossil record
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
.
Impact on the oceans
The coccolithophorids help in regulating the temperature of the oceans. They thrive in warm seas and release
dimethyl sulfide
Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
(DMS) into the air whose
nuclei help to produce thicker clouds to block the sun. When the oceans cool, the number of coccolithophorids decrease and the amount of clouds also decrease. When there are fewer clouds blocking the sun, the temperature also rises. This, therefore, maintains the balance and equilibrium of nature.
See also
*
CLAW hypothesis
The CLAW hypothesis proposes a negative 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 ...
*
Dimethyl sulfide
Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
*
Dimethylsulfoniopropionate
Dimethylsulfoniopropionate (DMSP), is an organosulfur compound with the formula (CH3)2S+CH2CH2COO−. This zwitterionic metabolite can be found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants ...
*
''Emiliania huxleyi'' virus 86
* ''
Pleurochrysis carterae
''Pleurochrysis carterae'' is a marine species of unicellular coccolithophorid algae 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 th ...
''
References
External links
Sources of detailed information
Nannotax3– illustrated guide to the taxonomy of coccolithophores and other nannofossils.
INA — International Nannoplankton Association''Emiliania huxleyi'' Home Page
Introductions to coccolithophores
*
ttp://www.paleoportal.org/index.php?globalnav=fossil_gallery§ionnav=taxon&taxon_id=104 The Paleontology Portal: Calcareous Nanoplanktonbr>
RadioLab– podcast on coccolithophores
{{Taxonbar, from=Q1647990
Haptophytes
Microfossils
Extant Late Triassic first appearances
Planktology
Sedimentology
de:Haptophyta