''Horastrea'' is a

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

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

Coscinaraeidae The Coscinaraeidae are a family of stony corals found in the Indo-Pacific region. Genera The World Register of Marine Species lists the following genera: *''Anomastraea'' Marenzeller, 1901 *'' Coscinaraea'' Milne Edwards & Haime, 1848 *'' C ...

. It is represented by the single species ''Horastrea indica'', the blister coral. It is native to the southwestern Indian Ocean where it is found in shallow water sandy reefs. It was first described by M Pichon in 1971. It is an uncommon coral and 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 ...

has assessed it as being 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, ...

Description

''H. indica'' forms massive solid

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'' ...

, usually hemispherical in shape. The individual

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 stony cups in which the polyps sit, are plocoid (surrounded by a wall) in smaller colonies, becoming meandroid (several corallites inside a valley) in larger ones. There are three cycles of

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five coun ...

(stony ridges) inside the calyx and these continue as well-developed costae between the corallites. This is a

zooxanthellate 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 ''Symbi ...

species containing microscopic

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

algae in the tissues which supplement the nutritional needs of the colony. This gives it a generally pale brown appearance, with contrasting oral discs of bluish-grey.

Distribution and habitat

''H. indica'' is found in the southwestern Indian Ocean, its range extending from Somalia, Kenya, Tanzania and Mozambique to Madagascar, the Comoros, Mayotte, Mauritius, Réunion and the Seychelles. It inhabits sandy reefs at depths of less than .

Status

''H. indica'' is an uncommon species of coral that was first described in 1971. Like other corals in the southwestern Indian Ocean, it faces threats from

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

, rising sea temperatures and the increasing occurrence of severe weather conditions. Bleaching events occur with rising sea temperatures and the corals become more prone to coral diseases.

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 ...

affects corals as does increased

siltation Siltation, is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or ...

from human developments and mechanical damage to reefs from fishing activities. Because of these factors, this coral's restricted range and its rarity, the

has assessed its conservation status as being " vulnerable".

References

{{Taxonbar, from1=Q20722465, from2=Q3938560 Coscinaraeidae Scleractinia genera Monotypic cnidarian genera Animals described in 1971