''Orbicella franksi'', commonly known as boulder star coral, is a

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

stony coral Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Merulinidae Merulinidae is a family of reef-building stony corals. Characteristics All the genera in this family are colonial, reef-building corals. Skeletal structures are similar to those of Faviidae but are highly fused, without paliform lobes. The vall ...

. It is native to shallow waters 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 Mexico ...

, the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

, the Bahamas, Bermuda and Florida, and is listed as a "

vulnerable species A vulnerable species is a species which has been Conservation status, categorized by the International Union for Conservation of Nature as being threatened species, threatened with extinction unless the circumstances that are threatened species, ...

" by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

Taxonomy

Until recently this coral, along with ''

Orbicella faveolata ''Orbicella faveolata'', commonly known as mountainous star coral, is a colonial stony coral in the family Merulinidae. ''Orbicella faveolata'' is native to the coral coast of the Caribbean Sea and the Gulf of Mexico and is listed as "endangered" ...

'', was thought to be a variety of ''

Orbicella annularis ''Orbicella annularis'', commonly known as the boulder star coral, is a species of coral that lives in the western Atlantic Ocean and is the most thoroughly studied and most abundant species of reef-building coral Corals are marine inverteb ...

''. There is very little morphological differences between them but studies have shown differences in corallite structure, life history,

allozyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that perfo ...

s and distribution. All three members of this

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

used to be placed in the genus ''Montastraea''.

Description

Colonies of ''Orbicella franksi'' usually form massive clumps with uneven surfaces, but sometimes forms plates, and in shady positions, may be encrusting. The general colour is orange-brown, greenish-brown or greyish-brown, but the extremities of the lumps are often pale or white. The

corallite A corallite is the skeletal cup, formed by an individual stony coral polyp, in which the polyp sits and into which it can retract. The cup is composed of aragonite, a crystalline form of calcium carbonate, and is secreted by the polyp. Corallit ...

s (the cups in which the polyps sit) are small, measuring across. The growing edges of this coral bear both large and small corallites which is in contrast to the closely related ''

'', which has regularly spaced corallites at its growing edges.

Distribution and habitat

''Orbicella franksi'' is native to the Caribbean Sea and the Gulf of Mexico, including Florida, the Bahamas and Bermuda. It typically grows on fore reefs (where it may be the most common species of coral) and its depth range is but it is typically found at depths of between .

Status

''Orbicella franksi'' seems to be more resistant to coral diseases than some members of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

, but is still susceptible to coral plague,

yellow-band disease Yellow-band disease (similar to Yellow Blotch disease) is a coral disease that attacks colonies of coral at a time when coral is already under stress from pollution, overfishing, and climate change. It is characterized by large blotches or patches ...

black band disease Black band disease is a coral disease in which corals develop a black band. It is characterized by complete tissue degradation due to a pathogenic microbial consortium. The mat is present between apparently healthy coral tissue and freshly expo ...

and

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 alg ...

. The major threats it faces include

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 ...

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 ...

and destruction of its reef habitat. The

has rated its conservation status as being near threatened.

References

{{Taxonbar, from=Q3933670 Merulinidae Coral reefs Animals described in 1895 ESA threatened species Taxobox binomials not recognized by IUCN