''Siderastrea radians'', also known as the lesser starlet coral or the shallow-water starlet coral, is a stony coral 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 ...

Siderastreidae Siderastreidae is a family of reef building stony corals. Members of the family include symbiotic algae called Zooxanthellae in their tissues which help provide their energy requirements. Description Members of this family are colonial, hermat ...

. It is found in shallow parts of the western Atlantic Ocean as small, solid mounds or encrusting sheets.

Description

''Siderastrea radians'' is either encrusting or grows in small, dimpled hummocks up to across but most

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'' ...

are much smaller than this. Occasionally it occurs as small

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 ad ...

pebbles that roll around in

seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...

s or as loose flat discs in shallow rocky places. The corallites are not circular but are triangular or four-sided and deep, with 30 to 40 small ridges called

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 c ...

. They have a dark interior that contrasts in colour with the pale surface of the coral which is greyish, greenish or light brown. The polyps are retracted back into these corallites during the day but emerge at night, extending their

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work ma ...

s to feed. Each of these has a small knob of stinging

cnidocyte A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this c ...

s at its tip. The lesser starlet coral can be confused with the closely related massive starlet coral (''

Siderastrea siderea ''Siderastrea siderea'', commonly known as massive starlet coral or round starlet coral, is a stony coral in the family Siderastreidae. It is found in shallow parts of the western Atlantic Ocean as solid boulder-shaped or domed structures. Desc ...

'') but that usually grows at greater depths, is larger and has less deep, more rounded corallites, each with 50 to 60 septa.

Distribution and habitat

''Siderastrea radians'' is common in tropical parts of the western Atlantic Ocean at depths of less than but is most common in under of water. Its range extends from Bermuda, the Bahamas, Florida and the Caribbean Sea south to Brazil and it also occurs in the eastern Atlantic off the coast of Africa. It is found on rocks in various reef habitats and can tolerate silty environments and

tide pool A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide. Many tide pool habitats are home to especially adaptable animals that ...

s. It is an adaptable species and in the Indian River Lagoon it has been found to tolerate temperatures varying between and and a wide range of salinities.

Biology

''Siderastrea radians'' feeds at night on

zooplankton 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 ...

which it catches with its tentacles. During the day it benefits from the symbiotic

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 ...

that are found in the tissues. These unicellular algae live within the host's cells and produce carbohydrates by

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 ...

and the coral makes use of these. The sexes are separate in the lesser starlet coral. Each of the twenty-eight ovaries in a female polyp produces a flattened oval

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

. Spawning takes place all through the year but may be related to the phase of the moon. Well developed

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 have been found being brooded inside female polyps shortly before the full moon. Growth rates of the lesser starlet coral are low but, because of its great tolerance to an increase in sediment levels and to elevated temperatures, it is an important species for maintaining and restoring damaged reefs and may be useful for this purpose if sea temperatures continue to rise.

References

{{Taxonbar, from=Q3945920 Siderastreidae Corals described in 1766 Taxa named by Peter Simon Pallas