''Isophyllia sinuosa'', the sinuous cactus coral, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 ) 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 ...

Mussidae Mussidae is a family of stony coral in the order Scleractinia. Following a taxonomic revision in 2012, the family is now restricted to species found in the Atlantic Ocean, with Pacific species transferred to the new family Lobophylliidae. Many ...

. It is found in shallow water in the tropical western Atlantic and the Caribbean Sea.

Description and habitat

''Isophyllia sinuosa'' is a massive coral that forms hemispherical or dome-shaped mounds up to across. On the coral surface there are shallow, meandering valleys about wide separated by convoluted ridges topped with a central, pale-coloured line. The polyps are large and are situated in the valleys, often in groups of three. Although they are usually retracted into their

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 by day, they are unable to retract completely, giving the coral a fleshy feel when touched. The septa that radiate from the corallites are spiny. At night, when the polyps are fully extended, the coral has a fuzzy appearance. The ridges and valleys are usually made up of contrasting colours. These combinations include green/yellow, green/blue, purplish-blue/white and two shades of brown.

Distribution

''Isophyllia sinuosa'' is found in the tropical west Atlantic. Its range includes the southern part of the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

, southern

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, the

Lesser Antilles The Lesser Antilles is a group of islands in the Caribbean Sea, forming part of the West Indies in Caribbean, Caribbean region of the Americas. They are distinguished from the larger islands of the Greater Antilles to the west. They form an arc w ...

, the

Bahamas The Bahamas, officially the Commonwealth of The Bahamas, is an archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of its population. ...

and

Bermuda Bermuda is a British Overseas Territories, British Overseas Territory in the Atlantic Ocean, North Atlantic Ocean. The closest land outside the territory is in the American state of North Carolina, about to the west-northwest. Bermuda is an ...

. It occurs on both back and fore reef slopes, on rocks, in

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s and among

seagrass Seagrasses are the only flowering plants which grow in marine (ocean), marine environments. There are about 60 species of fully marine seagrasses which belong to four Family (biology), families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and ...

es at depths down to about .

Biology

At night, the polyps of ''Isophyllia sinuosa'' extend their tentacles to feed 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 ...

. This coral is a

zooxanthella 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 ...

te species, which means that it harbours

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

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s (unicellular algae) in its tissues. These contain

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

and can provide the coral with organic carbon compounds 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 ...

. These are important to the coral and provide up to 50% of its nutrient requirements. A well-lit position is essential to zooxanthellate corals and ''Isophyllia sinuosa'' is one of the most aggressive corals, defending itself from the risk of being over-shadowed. It is reported to attack other corals or sponges in its close vicinity using an extracoelentric feeding mechanism in which specialised filament-like tentacles extend onto the living tissues of the neighbouring organisms, secreting enzymes which digest them

in situ is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...

Status

''Isophyllia sinuosa'' has a wide range but is generally an uncommon species. It is considered by the

IUCN Red List of Threatened Species The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological spe ...

to be of "

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

" as its population is believed to be stable. It is prone to

bleaching Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...

, when a coral expels its zooxanthellae under stressful conditions, to

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 expos ...

, and to white plague. As a shallow water species it shares the threats posed to coral reefs in general which include a rise in sea temperatures,

ocean acidification Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ...

, coral diseases, storm damage, sedimentation, and human activities.

References

{{Taxonbar, from=Q3155601 Mussinae Cnidarians of the Atlantic Ocean Cnidarians of the Caribbean Sea Fauna of the Bahamas Fauna of the Lesser Antilles Fauna of Bermuda Corals described in 1786