''Astrangia poculata'', the northern star coral or northern cup coral, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of non-reefbuilding

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 mo ...

in the

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

Rhizangiidae. It is native to shallow water in the western Atlantic Ocean and the Caribbean Sea. It is also found on the western coast of Africa. The International Union for Conservation of Nature lists this coral as being of "

least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. ...

". ''Astrangia poculata'' is an emerging model organism for corals because it harbors a facultative photosymbiosis, is a calcifying coral, and has a large geographic range. Research on this emerging model system is showcased annually by the Astrangia Research Working Group, collaboratively hosted by Roger Williams University, Boston University, and Southern Connecticut State University

Description

''Astrangia poculata'' grows in small clumps that are up to across. The individual polyps are large and sit in stony cups known as

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. Corall ...

s. The polyps are translucent and the colony has a furry appearance when they are expanded. In warm water and with high levels of light, this coral often houses

photosynthesizing 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 ...

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 para ...

protists known as

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 ...

in its tissues, and then the coral appears brown. In cooler, or low-light conditions, the zooxanthellae may no longer be beneficial to the coral and may be expelled, and then the coral appears pale in colour. It can be confused with the southern cup coral (''Astrangia solitaria''), but that species has a more southerly distribution, is generally brown, may be solitary, has larger corallites wide with 36 septa (stony ridges), and does not contain zooxanthellae.

Distribution and habitat

''Astrangia poculata'' is native to the western Atlantic Ocean and

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 ...

where its range extends from

Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mont ...

Massachusetts Massachusetts (Massachusett: ''Muhsachuweesut Massachusett_writing_systems.html" ;"title="nowiki/> məhswatʃəwiːsət.html" ;"title="Massachusett writing systems">məhswatʃəwiːsət">Massachusett writing systems">məhswatʃəwiːsət'' En ...

to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an 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 United ...

. It also occurs on the western coast of Africa. It occurs in encrusting clumps on rocks and is common under ledges and boulders, on pilings and on wrecks. It also occurs in deep water and detached clumps sometimes get washed up on shore.

Biology

Reproduction of ''Astrangia poculata'' takes place during the summer when eggs and sperm are liberated into 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 ...

and fertilisation takes place. The

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s hatch into

planula A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores. Some groups of Nemerteans also produce larvae that are very similar to the planula, which ...

larvae which drift with the

plankton 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 cruc ...

before settling to the seabed and undergoing

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 polyps. Among zooxanthelate organisms, ''A. poculata'' is one of the few to have been studied with regard to the acquisition of zooxanthellae. It was found that there was no routine transfer of these symbionts from parent to offspring. The polyps spread their tentacles to feed, gathering plankton and other food particles from the water passing by. The

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' ...

grows by budding, and in favourable conditions, the clump can grow at the rate of one new polyp every three days. In colder conditions it may stop growing and the coenosarc (soft tissues) may die back to some extent or lose symbionts via expulsion, rendering the stony skeleton prone to being fouled by other organisms and undergoing a winter quiescence. The base often hosts various boring or burrowing

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

invertebrates. Both temperature and symbiosis are known to influence the condition of the coral host, specifically with regards to wound-healing ability, but it is primarily season that drives microbiome structure in Rhode Island populations of the coral.

References

{{Taxonbar, from=Q3943800 Rhizangiidae Corals described in 1786