''Isophyllia sinuosa'', the sinuous cactus 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 appropriate s ...

of stony coral in the

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

Mussidae. 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 ( es, Golfo de México) is an oceanic basin, 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

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 Mexico ...

, southern

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, the

Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc betwe ...

, the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the Atlantic Ocean, North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to ...

and

Bermuda ) , anthem = "God Save the King" , song_type = National song , song = " Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , e ...

. 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'') a ...

s and among

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

es at depths down to about .

Biology

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

. This coral is a zooxanthellate species, which means that it harbours

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 ...

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

s (unicellular algae) in its tissues. These contain

chlorophyll Chlorophyll (also chlorophyl) 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 allow plants to a ...

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

. 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.

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 the world's most comprehensive inventory of the global conservation status of biologi ...

to be 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. T ...

" 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 (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

, when a coral expels its zooxanthellae under stressful conditions, to black band disease, 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 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 ...

, 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