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: ''This is about the genus sometimes called Zoox. For the company, see Zoox (company)'' ''Symbiodinium'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
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 that encompasses the largest and most prevalent group of
endosymbiotic An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
dinoflagellates known. These unicellular
microalgae Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist indiv ...
commonly reside in the
endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
of tropical
cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...
ns such as
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
s,
sea anemone Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...
s, and
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbre ...
, where the products of their photosynthetic processing are exchanged in the host for inorganic molecules. They are also harbored by various species of
demosponge Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). They are sponges with a soft body that covers a har ...
s, flatworms,
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
such as the giant clams,
foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...
( soritids), and some ciliates. Generally, these
dinoflagellates 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 ...
enter the host cell through
phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
, persist as
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
symbionts, reproduce, and disperse to the environment. The exception is in most mollusks, where these symbionts are intercellular (between the cells).
Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...
ns that are associated with ''Symbiodinium'' occur mostly in warm
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 o ...
(nutrient-poor),
marine environments Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental a ...
where they are often the dominant constituents of
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 " ...
communities. These dinoflagellates are therefore among the most abundant
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s found in
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
ecosystems. ''Symbiodinium'' are colloquially called
zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''S ...
, and animals symbiotic with algae in this genus are said to be "zooxanthellate". The term was loosely used to refer to any golden-brown
endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
s, including
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 se ...
s and other dinoflagellates. Continued use of the term in the scientific literature is discouraged because of the confusion caused by overly generalizing taxonomically diverse symbiotic relationships. In 2018, the systematics of Symbiodiniaceae was revised, and the distinct
clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English te ...
have been reassigned into seven genera. Following this revision, the name ''Symbiodinium'' is now ''
sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
'' a genus name for only species that were previously classified as Clade A. The other clades were reclassified as distinct genera (see
Molecular Systematics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
below).


Intracellular symbionts

Many ''Symbiodinium'' species are known primarily for their role as mutualistic endosymbionts. In
hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host ...
, they usually occur in high densities, ranging from hundreds of thousands to millions per square centimeter. The successful culturing of swimming gymnodinioid cells from coral led to the discovery that "zooxanthellae" were actually dinoflagellates. Each ''Symbiodinium'' cell is coccoid ''in hospite'' (living in a host cell) and surrounded by a membrane that originates from the host cell plasmalemma during
phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
. This membrane probably undergoes some modification to its
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
content, which functions to limit or prevent phago-lysosome fusion. The
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...
structure containing the symbiont is therefore termed the symbiosome. A single symbiont cell occupies each symbiosome. It is unclear how this membrane expands to accommodate a dividing symbiont cell. Under normal conditions, symbiont and host cells exchange
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
and
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
s that enable the growth and proliferation of both partners.


Natural services and economic value

''Symbiodinium'' is one of the most studied symbionts. Their mutualistic relationships with reef-building corals form the basis of a highly diverse and productive
ecosystem 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 syst ...
. Coral reefs have economic benefits – valued at hundreds of billions of
dollars Dollar is the name of more than 20 currencies. They include the Australian dollar, Brunei dollar, Canadian dollar, Hong Kong dollar, Jamaican dollar, Liberian dollar, Namibian dollar, New Taiwan dollar, New Zealand dollar, Singapore dollar, U ...
each year – in the form of ornamental,
subsistence A subsistence economy is an economy directed to basic subsistence (the provision of food, clothing, shelter) rather than to the market. Henceforth, "subsistence" is understood as supporting oneself at a minimum level. Often, the subsistence econo ...
and
commercial Commercial may refer to: * a dose of advertising conveyed through media (such as - for example - radio or television) ** Radio advertisement ** Television advertisement * (adjective for:) commerce, a system of voluntary exchange of products and s ...
fisheries, tourism and recreation, coastal protection from storms, a source of
bioactive compound A bioactive compound is a compound that has an effect on a living organism, tissue or cell, usually demonstrated by basic research in vitro or in vivo in the laboratory. While dietary nutrients are essential to life, bioactive compounds have not ...
s for
pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
development, and more.


Coral bleaching

The study of ''Symbiodinium'' biology is driven largely by a desire to understand global coral reef decline. A chief mechanism for widespread reef degradation has been stress-induced
coral bleaching Coral bleaching is the process when corals become white due to various stressors, such as changes in temperature, light, or nutrients. Bleaching occurs when coral polyps expel the zooxanthellae ( dinoflagellates that are commonly referred to as ...
caused by unusually high
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
temperature. Bleaching is the disassociation of the coral and the symbiont and/or loss of
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
within the alga, resulting in a precipitous loss in the animal's pigmentation. Many ''Symbiodinium''-cnidarian associations are affected by sustained elevation of sea surface temperatures, but may also result from exposure to high
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
levels (including UVR), extreme low temperatures, low salinity and other factors. The bleached state is associated with decreased host
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 M ...
, increased disease susceptibility and, if prolonged, partial or total mortality. The magnitude of mortality from a single bleaching event can be global in scale as it was in 2015. These episodes are predicted to become more common and severe as temperatures worldwide continue to rise. The physiology of a resident ''Symbiodinium'' species often regulates the bleaching susceptibility of a coral. Therefore, a significant amount of research has focused on characterizing the physiological basis of thermal tolerance and in identifying the ecology and distribution of thermally tolerant symbiont species. The symbiosis ''Symbodinium''-coral could provide higher resistance to multiple stress (
desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...
, high UVR) to the coral holobiont through its
mycosporine-like amino acid Mycosporine-like amino acids (MAAs) are small secondary metabolites produced by organisms that live in environments with high volumes of sunlight, usually marine environments. The exact number of compounds within this class of natural products is ye ...
s (MAAs). The concentration of MAAs increases with stress and ROS in ''Symbodinium''. These UV-absorbing MAAs may also support light-harvesting pigments during photosynthesis, be source of nitrogen storage and for reproduction. More than half of the ''Symbodinium'' taxa contain MAAs. '' Symbiodinium trenchi'' is a stress-tolerant species and is able to form mutualistic relationships with many species of coral. It is present in small numbers in coral globally and is common in the
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated fro ...
, where the water is about 4 °C (7 °F) warmer than in other parts of the
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by ...
. In the
Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexic ...
in late 2005, water temperature was elevated for several months and it was found that ''S. trenchi'', a symbiont not normally abundant, took up residence in many corals in which it had not previously been observed. Those corals did not bleach. Two years later, it had largely been replaced as a symbiont by the species normally found in the Caribbean. ''S. thermophilum'' was recently found to make up the bulk of the algal population inside the corals of the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a mediterranean sea in Western Asia. The bo ...
. It is also present in the
Gulf of Oman The Gulf of Oman or Sea of Oman ( ar, خليج عمان ''khalīj ʿumān''; fa, دریای عمان ''daryâ-ye omân''), also known as Gulf of Makran or Sea of Makran ( ar, خلیج مکران ''khalīj makrān''; fa, دریای مکرا� ...
and the
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...
, at a much lower concentration. Coral that hosted this species was able to tolerate the waters of the Persian Gulf, much hotter than the of coral reefs globally.


Molecular systematics

The advent of
DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. T ...
comparison initiated a rebirth in the ordering and naming of all organisms. The application of this methodology helped overturn the long-held belief that (traditional understood) ''Symbiodinium'' comprised a single genus, a process which began in earnest with the morphological,
physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
, and
biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...
comparisons of cultured isolates. Currently,
genetic marker A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...
s are exclusively used to describe
ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
patterns and deduce
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary relationships among morphologically
cryptic Cryptic may refer to: In science: * Cryptic species complex, a group of species that are very difficult to distinguish from one another * Crypsis, the ability of animals to blend in to avoid observation * Cryptic era, earliest period of the Earth ...
members of this group. Foremost in the molecular systematics of ''Symbiodinium'' is to resolve ecologically relevant units of diversity (i.e. species).


Phylogenetic disparity among "clades"

The earliest ribosomal gene sequence data indicated that ''Symbiodinium'' had lineages whose genetic divergence was similar to that seen in other dinoflagellates from different
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
, families, and even
orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
. This large phylogenetic disparity among clades A, B, C, etc. was confirmed by analyses of the sequences of the mitochondrial gene coding for
cytochrome c oxidase subunit I Cytochrome c oxidase I (COX1) also known as mitochondrially encoded cytochrome c oxidase I (MT-CO1) is a protein that in humans is encoded by the ''MT-CO1'' gene. In other eukaryotes, the gene is called ''COX1'', ''CO1'', or ''COI''. Cytoch ...
(CO1) among Dinophyceae. Most of these clade groupings comprise numerous reproductively isolated, genetically distinct lineages (see ‘Species diversity’), exhibiting different ecological and biogeographic distributions (see ‘Geographic distributions and patterns of ‘diversity’). Recently (2018), these distinct clades within the family of Symbiodiniaceae have been reassigned, although not exclusively, into seven genera: ''Symbiodinium'' (understood ''
sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
'', i. e. clade A), '' Breviolum'' (clade B), '' Cladocopium'' (clade C), '' Durusdinium'' (clade D), '' Effrenium'' (clade E), '' Fugacium'' (clade F), and '' Gerakladium'' (clade G).


Species diversity

The recognition of species diversity in this genus remained problematic for many decades due to the challenges of identifying morphological and biochemical traits useful for diagnosing species. Presently, phylogenetic, ecological, and population genetic data can be more rapidly acquired to resolve ''Symbiodinium'' into separate entities that are consistent with Biological, Evolutionary, and Ecological Species Concepts. Most genetics-based measures of diversity have been estimated from the analysis of one
genetic marker A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...
(e. g. LSU,
ITS2 Internal transcribed spacer (ITS) is the spacer DNA situated between the small-subunit ribosomal RNA (rRNA) and large-subunit rRNA genes in the chromosome or the corresponding transcribed region in the polycistronic rRNA precursor transcript. ...
, or cp23S), yet in recent studies these and other markers were analyzed in combination. The high concordance found among nuclear, mitochondrial and chloroplast DNA argues that a hierarchical phylogenetic scheme, combined with ecological and population genetic data, can unambiguously recognize and assign
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally ag ...
to reproductively isolated lineages, i.e. species. The analysis of additional phylogenetic markers show that some ''Symbiodinium'' that were initially identified by slight differences in ITS sequences may comprise members of the same species whereas, in other cases, two or more genetically divergent lineages can possess the same ancestral ITS sequence. When analysed in the context of the major species concepts, the majority of ITS2 sequence data provide a reasonable proxy for species diversity. Currently, ITS2 types number in the hundreds, but most communities of symbiotic cnidaria around the world still require comprehensive sampling. Furthermore, there appears to be a large number of unique species found in association with equally diverse species assemblages of soritid foraminifera, as well as many other ''Symbiodinium'' that are exclusively free-living and found in varied, often
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 " ...
,
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s. Given the potential species diversity of these ecologically cryptic ''Symbiodinium'', the total species number may never be accurately assessed.


Clone diversity and population genetics

Through the use of
microsatellite A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...
markers, multilocus genotypes identifying a single clonal line of ''Symbiodinium'' can be resolved from samples of host tissue. It appears that most individual
colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...
harbor a single multilocus genotype (i.e. clone). Extensive sampling within colonies confirms that many colonies harbor a
homogeneous Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
(clonal) ''Symbiodinium'' population. Additional genotypes do occur in some colonies, yet rarely more than two or three are found. When present in the same colony, multiple clones often exhibit narrow zones of overlap. Colonies adjacent to each other on a reef may harbor identical clones, but across the host population the clone diversity of a particular ''Symbiodinium'' species is potentially large and comprises recombinant
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 that are the product of
sexual recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryot ...
. A clone tends to remain dominant in a colony over many months and years, but may be occasionally displaced or replaced. The few studies examining clone dispersal find that most genotypes have limited geographic distributions, but that dispersal and gene flow is likely influenced by host life history and mode of symbiont acquisition (e. g. horizontal vs. vertical).


Species diversity, ecology, and biogeography


Geographic distributions and patterns of diversity

''Symbiodinium'' are perhaps the best group for studying micro-eukaryote
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
and
ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...
for several reasons. Firstly, available phylogenetic and population
genetic marker A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...
s allow for detailed examination of their
genetic diversity Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is dis ...
over broad spatial and temporal scales. Also, large quantities of ''Symbiodinium'' cells are readily obtained through the collection of
hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host ...
that harbor them. Lastly, their association with animals provides an additional axis by which to compare and contrast ecological distributions. The earliest genetic methods for assessing ''Symbiodinium'' diversity relied on low-resolution molecular markers that separated the genus into a few evolutionarily divergent lineages, referred to as "
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
s". Previous characterizations of geographic distribution and dominance have focused on the clade-level of genetic resolution, but more detailed assessments of diversity at the species level are needed. While members of a given clade may be ubiquitous, the species diversity within each clade is potentially large, with each species often having different ecological and geographic distributions related to their dispersal ability, host biogeography, and external environmental conditions. A small number of species occur 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 ...
environments where few symbiotic animals occur. As a result, these high latitude associations tend to be highly species specific.


Species diversity assigned to different ecological guilds

The large diversity of ''Symbiodinium'' revealed by genetic analyses is distributed non-randomly and appears to comprise several
guilds A guild ( ) is an association of artisans and merchants who oversee the practice of their craft/trade in a particular area. The earliest types of guild formed as organizations of tradesmen belonging to a professional association. They sometimes ...
with distinct ecological habits. Of the many ''Symbiodinium'' characterized genetically, most are host-specific, mutualistic, and dominate their host. Others may represent compatible symbionts that remain as low-abundance background populations because of competitive inferiority under the prevailing external environmental conditions (e.g. high light vs. low light). Some may also comprise opportunistic species that may proliferate during periods of physiological stress and displace the normal resident symbiont and remain abundant in the host's tissues for months to years before being replaced by the original symbiont. There are also those that rapidly infect and establish populations in host juveniles until being replaced by symbionts that normally associate with host adult colonies. Finally, there appears to be another group of ''Symbiodinium'' that are incapable of establishing endosymbiosis yet exist in environments around the animal or associate closely with other substrates (i.e. macro-algal surfaces,
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
surface) ''Symbiodinium'' from functional groups 2, 3, and 4 are known to exist because they culture easily, however species with these life histories are difficult to study because of their low abundance in the environment.


Free-living and "non-symbiotic" populations

There are few examples of documented populations of free-living ''Symbiodinium''. Given that most host larvae must initially acquire their symbionts from the environment, viable ''Symbiodinium'' cells occur outside the host. The motile phase is probably important in the external environment and facilitates the rapid infection of host larvae. The use of aposymbiotic host polyps deployed as "capture vessels" and the application of molecular techniques has allowed for the detection of environmental sources of ''Symbiodinium''. With these methods employed, investigators may resolve the distribution of different species on various benthic surfaces and cell densities suspended in the
water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...
. The genetic identities of cells cultured from the environment are often dissimilar to those found in hosts. These likely do not form endosymbioses and are entirely free-living; they are different from "dispersing" symbiotic species. Learning more about the "private lives" of these environmental populations and their ecological function will further our knowledge about the diversity, dispersal success, and evolution among members within this large genus.


Culturing

Certain ''Symbiodinium'' strains and/or species are more easily cultured and can persist in artificial or supplemented seawater media (e.g. ASP–8A, F/2) for decades. The comparison of cultured isolates under identical conditions show clear differences in morphology, size, biochemistry, gene expression, swimming behavior, growth rates, etc. This pioneering comparative approach initiated a slow paradigm shift in recognizing that the traditional genus ''
sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
'' comprised more than a single real genus. Culturing is a selective process, and many ''Symbiodinium'' isolates growing on artificial media are not typical of the species normally associated with a particular host. Indeed, most host–specific species have yet to be cultured. Samples for genetic analysis should be acquired from the source
colony In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state' ...
in order to match the resulting culture with the identity of the dominant and ecologically relevant symbiont originally harbored by the animal.


Life cycle

The life cycle of ''Symbiodinium'' was first described from cells growing in culture media. For isolates that are in log phase growth, division rates occur every 1–3 days, with ''Symbiodinium'' cells alternating between a spherical, or coccoid, morphology and a smaller
flagellated 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#Cellular level, motility. Many protists with flagella are termed as flagellates. A m ...
motile mastigote stage. While several similar schemes are published that describe how each morphological state transitions to other, the most compelling life history reconstruction was deduced from
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
and
electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
and
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...
staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in th ...
evidence. During asexual propagation (sometimes referred to as mitotic or vegetative growth), cells undergo a diel cycle of
karyokinesis 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 maintai ...
(
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
/nuclear division) in darkness. The mother cell then divides (
cytokinesis Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and mei ...
) soon after exposure to light and releases two motile cells. The initiation and duration of motility varies among species. Approaching or at the end of the
photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
the mastigotes cease swimming, release their
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 fro ...
, and undergo a rapid
metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
into the coccoid form. As cultures reach stationary growth phase, fewer and fewer motile cells are observed, indicating slower division rates. Large tetrads are occasionally observed, particularly when cells in stationary growth phase are transferred to fresh media. However, it is unknown whether this stage is the product of two consecutive mitotic divisions, or perhaps a process that generates sexually competent motile cells (i.e.
gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
s), or is the end result of meiosis (i. e. as meiotic tetrads) following gamete fusion. There is no cytological evidence for sexual recombination, and meiosis has never been observed, but population genetic evidence supports the view that ''Symbiodinium'' periodically undergo events of sexual recombination. How, when, and where the sexual phase in their life history occurs remains unknown.


Morphology

The morphological description of the genus ''Symbiodinium'' is originally based on the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...
(
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...
) ''S. microadriaticum''. Because these dinoflagellates possess two major stages in their life history (see above), namely the mastigote (motile) and coccoid (non-motile) stages, the morphology of both is described in order to provide a complete diagnosis of the organism.


Flagellated (mastigote) cell

The motile
flagellated 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#Cellular level, motility. Many protists with flagella are termed as flagellates. A m ...
form is gymnodinioid and athecate ("nude"). The relative dimensions of the epicone and hypocone differ among species. The
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
are most visible in the motile phase but lack fibrous cellulosic structures found in thecate ("armored") dinoflagellates. Between the points of origin of the two flagella is an extensible structure of unknown function called the peduncle. In other dinoflagellates, an analogous structure has been implicated in
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 ...
feeding and
sexual recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryot ...
. In ''Symbiodinium'', it has been suggested that the peduncle may be involved in substrate attachment, explaining why certain cells seem to spin in place. Compared to other gymnodinioid genera, there is little or no displacement at the sulcus where the ends of the cingulum (or cigulum) groove converge. The internal organelles of the mastigote are essentially the same as described in the coccoid cell (see below). The transition from mastigote to coccoid stage in ''Symbiodinium'' occurs rapidly, but details about cellular changes are unknown. Mucocysts (an ejectile organelle) located beneath the plasmalemma are found in ''S. pilosum'' and their function is unknown, but may be involved in heterotrophic feeding.


Coccoid cell

The coccoid cell of ''Symbiodinium'' is spherical and ranges in average diameter from 6 to 13 µm, depending on the species (Blank et al. 1989). This stage is often wrongly interpreted as a
dinocyst Dinocysts or dinoflagellate cysts are typically 15 to 100 µm in diameter and produced by around 15–20% of living dinoflagellates as a dormant, zygotic stage of their lifecycle, which can accumulate in the sediments as microfossils. Organic- ...
; hence, in published literature, the alga in hospite is often referred to as a vegetative cyst. The term ''cyst'' usually refers to a dormant, metabolically quiescent stage in the life history of other dinoflagellates, initiated by several factors, including nutrient availability, temperature, and day length. Such cysts permit extended resistance to unfavourable environmental conditions. Instead, coccoid ''Symbiodinium'' cells are metabolically active, as they photosynthesize, undergo mitosis, and actively synthesize proteins and nucleic acids. While most dinoflagellates undergo mitosis as a mastigote, in ''Symbiodinium'', mitosis occurs exclusively in the coccoid cell.


Cell wall

The coccoid cell is surrounded by a cellulosic, usually smooth
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...
that contains large-molecular-weight proteins and glycoproteins. Cell walls grow thicker in culture than in ''hospite''. The cell membrane ( plasmalemma) is located beneath the cell wall, yet little is known about its composition and function in terms of the regulation of trans-membrane transport of
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...
s. During
karyokinesis 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 maintai ...
and
cytokinesis Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and mei ...
, the cell wall remains intact until the mastigotes escape the mother cell. In culture, the discarded walls accumulate at the bottom of the culture vessel. It is not known what becomes of the walls from divided cells in ''hospite''. One species, ''S. pilosum'', possesses tufts of hair-like projections from the cell wall; this is the only known surface characteristic used to diagnose a species in the genus.


Chloroplast

Most described species possess a single, peripheral, reticulated
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it i ...
bounded by three membranes. The volume of the cell occupied by the chloroplast varies among species. The lamellae comprise three closely appressed (stacked)
thylakoid Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thyl ...
s, and are attached by two stalks to the pyrenoid surrounded by a
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...
sheath. In three of the described species, the thylakoids are in parallel arrays, but in ''S. pilosum'', there are also peripheral lamellae. There are no thylakoid membranes invading the pyrenoid, which is unlike other symbiotic dinoflagellates. The
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...
components of thylakoids include the galactolipids as monogalactosyl-diglycerides (MGDG) and digalactosyl-diglycerides( DGDG),; the sulpholipid sulphoquinovosyl-diglyceride (SQDG), phosphatidyl glycerol, and phosphatidyl choline. Associated with these are various
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
s. The light-harvesting and reaction centre components in the thylakoid membrane include a water-soluble peridinin-chlorophyll a-protein complex (PCP or PerCP), and a membrane-bound chlorophyll a-chlorophyll c2-peridinin-protein-complex (acpPC), along with typical photosynthetic electron transport systems such as the
photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosyst ...
reaction centre and the chlorophyll-a-P700 reaction centre complex of
photosystem I Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane protein complex that us ...
. Also associated with the thylakoids are the
xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek (, "yellow") and (, "lea ...
s
dinoxanthin Dinoxanthin is a type of xanthophyll found in dinoflagellates. This compound is a potential antioxidant and may help to protect dinoflagellates against reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive ch ...
, diadinoxanthin,
diatoxanthin Diatoxanthin is a type of xanthophyll found in phytoplankton and diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, ...
and the
carotene The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the ex ...
, β-Carotene. The pyrenoid contains the
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...
- encoded
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
type II Ribulose-1,5-bis-phosphate-carboxylase-oxygenase (
RuBisCO Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...
), which is responsible for the
catalysis Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
of inorganic
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 t ...
(CO2) into
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s. All cultured isolates (i.e. strains) are capable of
phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
adjustment in their capacity for light harvesting (i.e. photoacclimation), such as by altering the cellular Chl. ''a'' and peridinin quota, as well as the size and number of photosynthetic units. However, the ability to acclimate is a reflection of genetic differences among species that are differently adapted (evolved) to a particular photic environment. For example, ''S. pilosum'' is characterized as a high light-adapted species, while others are low light-adapted (''S. kawagutii'') or adapted to a larger range in varying light fields (''S. microadriaticum'').


Nucleus

In general, 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 Nucl ...
is centrally located and the
nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of sign ...
is often associated with the inner
nuclear membrane The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material. The nuclear envelope consists of two lipid bilayer membra ...
. The
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
s, as in other dinoflagellates, are seen as ‘permanently super-coiled’ DNA in transmission electron micrographs (TEM). The described species of ''Symbiodinium'' possess distinct chromosome numbers (ranging from 26 to 97), which remain constant throughout all phases of the nuclear cycle. However, during M-phase, the volume of each chromosome is halved, as is the volume of each of the two resulting nuclei. Thus, the ratio of chromosome volume to nuclear volume remains constant. These observations are consistent with the interpretation that the algae are
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, respective ...
, a conclusion supported by molecular genetic data. During S-phase of the nuclear cycle the chromosomes do uncoil to facilitate DNA synthesis, and the volumes of both the chromosomes and the nucleus return to those seen in the G22 phase.


Other cytoplasmic organelles

There are several additional organelles found in the cytoplasm of ''Symbiodinium''. The most obvious of these is the structure referred to as the "accumulation body". This is a membrane-bound
vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...
(
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...
) with contents that are unrecognizable, but appear red or yellow under the light microscope. It may serve to accumulate cellular debris or act as an autophagic vacuole in which non-functional organelles are digested and their components recycled. During mitosis, only one daughter cell appears to acquire this structure. There are other vacuoles that may contain membranous inclusions, while still others contain crystalline material variously interpreted as
oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...
crystals or crystalline
uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...
.


Species

The following species are recognised by the World Register of Marine Species: *'' Symbiodinium bermudense'' R.K.Trench, 1993 *'' Symbiodinium californium'' A.T.Banaszak, R.Iglesias-Prieto & R.K.Trench, 1993 *'' Symbiodinium cariborum'' R.K.Trench, 1993 *'' Symbiodinium corculorum'' R.K.Trench, 1993 *'' Symbiodinium glynnii'' D.C.Wham, G.Ning, T.C.LaJeunesse, 2017 *'' Symbiodinium goreaui'' Trench & Blank, 2000 *'' Symbiodinium kawagutii'' Trench & Blank, 2000 *'' Symbiodinium meandrinae'' R.K.Trench, 1993 *'' Symbiodinium microadriaticum'' Freudenthal, 1962 *'' Symbiodinium minutum'' T.C.LaJeunesse, J.E. Parkinson & J.D.Reimer, 2012 *'' Symbiodinium pilosum'' Trench & Blank, 2000 *'' Symbiodinium psygmophilum'' LaJeunesse, T.C., Parkinson, J.E. & Reimer, J.D., 2012 *'' Symbiodinium pulchrorum'' R.K.Trench, 1993 * '' Symbiodinium thermophilum'', new species Algal species helps corals survive in Earth's hottest reefs
/ref>


References


External links

*
An image
of ''Symbiodinium'' a
Smithsonian Ocean Portal
{{Taxonbar, from=Q10375461 Dinophyceae Dinoflagellate genera Symbiosis