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

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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, her ...

. 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 A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their '' metropole'' (or "mother country"). This separated rule was often or ...

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 (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

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

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 are not circular but are triangular or four-sided and deep, with 30 to 40 small ridges called

septa SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

. 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 main ...

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

cnidocyte A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s at its tip. The lesser starlet coral can be confused with the closely related massive starlet coral ('' Siderastrea siderea'') 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. These pools typically range from a few inches to a few feet deep and a few feet across. Many of these pools exist as separate bodies of water only ...

s. It is an adaptable species and in the

Indian River Lagoon The Indian River Lagoon is a grouping of three lagoons: the Mosquito Lagoon, the Banana River, and the Indian River, on the Atlantic Coast of Florida; one of the most biodiverse estuaries in the Northern Hemisphere and is home to more than 4, ...

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 heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

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

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

zooxanthellae Zooxanthellae (; zooxanthella) is a colloquial term for single-celled photosynthetic organisms that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, demosponges, and nudibranchs. Most known zooxanthell ...

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

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

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 ...

. 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, which are not related to cnidarians at all. Some groups of Nemerteans also produce larva ...

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