Isophyllia sinuosa
A stony coral with aggressive extracoelentric feeding and symbiotic algae.
Isophyllia sinuosa, called the sinuous cactus coral, is a stony coral belonging to the family Mussidae. It lives in shallow waters across the tropical western Atlantic and the Caribbean Sea.
This coral grows as massive, dome-shaped mounds up to 20 cm across. Its surface is marked by shallow, winding valleys about 22 mm wide, separated by convoluted ridges that have a pale line running down the center. Large polyps sit in these valleys, often in groups of three. During the day, the polyps stay mostly retracted but cannot pull in completely, giving the coral a fleshy texture. The radiating septa are spiny. At night, when the polyps extend fully, the coral looks fuzzy. The ridges and valleys usually show contrasting colors, such as green and yellow, green and blue, purplish-blue and white, or two shades of brown.
The species ranges across the tropical west Atlantic, including the southern Gulf of Mexico, the Caribbean Sea, southern Florida, the Lesser Antilles, the Bahamas, and Bermuda. It lives on back and fore reef slopes, rocks, lagoons, and among seagrasses, down to about 15 meters deep.
At night, the polyps extend their tentacles to feed on zooplankton. Isophyllia sinuosa is zooxanthellate, hosting symbiotic dinoflagellates in its tissues. These algae use chlorophyll to photosynthesize, supplying the coral with organic carbon compounds that meet up to 50% of its nutrient needs. Because it relies on light, this coral is highly aggressive, defending itself from being shaded. It attacks nearby corals or sponges using an extracoelentric feeding mechanism: specialized filament-like tentacles extend onto the neighbor’s tissues and secrete enzymes that digest them on the spot.
Though widespread, Isophyllia sinuosa is generally uncommon. The IUCN Red List considers it of Least Concern, as its population appears stable. It is prone to bleaching (expelling its zooxanthellae under stress), black band disease, and white plague. As a shallow-water species, it faces the same threats as coral reefs overall: rising sea temperatures, ocean acidification, coral diseases, storm damage, sedimentation, and human activities.
Quick Facts
- Taxon
- Isophyllia sinuosa
Facts from the source article.
Lore & Background
Isophyllia sinuosa forms massive, hemispherical or dome-shaped mounds up to 20 cm across. Its surface features shallow, meandering valleys about 22 mm wide, separated by convoluted ridges topped with a pale central line. The polyps are large and situated in the valleys, often in groups of three; they are usually retracted by day but cannot retract completely, giving the coral a fleshy feel. The septa radiating from the corallites are spiny. At night, when polyps extend fully, the coral appears fuzzy. Ridges and valleys typically show contrasting colors, such as green/yellow, green/blue, purplish-blue/white, or two shades of brown.
This species is found in the tropical west Atlantic, including the southern Gulf of Mexico, the Caribbean Sea, southern Florida, the Lesser Antilles, the Bahamas, and Bermuda. It occurs on back and fore reef slopes, on rocks, in lagoons, and among seagrasses down to about 15 meters depth.
Isophyllia sinuosa is a zooxanthellate coral, harboring symbiotic dinoflagellates that provide organic carbon compounds via photosynthesis, supplying up to 50% of its nutrient needs. It is one of the most aggressive corals, defending itself from being overshadowed by attacking other corals or sponges with an extracoelentric feeding mechanism: specialized filament-like tentacles extend onto neighboring organisms, secreting enzymes that digest them in situ.
Reader's Guide
Isophyllia sinuosa is significant as a zooxanthellate species that relies on symbiotic algae for up to half its nutrients, making a well-lit position essential. Its aggressive extracoelentric feeding mechanism, used to attack nearby corals or sponges, distinguishes it as one of the most aggressive corals. The species has a wide range across the tropical western Atlantic and Caribbean, but is generally uncommon. According to the IUCN Red List, it is considered of Least Concern with a stable population. However, it is prone to bleaching, black band disease, and white plague. As a shallow-water species, it shares threats common to coral reefs, including rising sea temperatures, ocean acidification, coral diseases, storm damage, sedimentation, and human activities. Its contrasting color combinations and inability to fully retract polyps give it a distinctive fleshy texture.
Did You Know?
- The polyps of Isophyllia sinuosa are unable to retract completely, giving the coral a fleshy feel when touched.
- It attacks other corals or sponges using an extracoelentric feeding mechanism with filament-like tentacles that secrete digestive enzymes.
- Its symbiotic dinoflagellates provide up to 50% of the coral's nutrient requirements through photosynthesis.
- The ridges and valleys of this coral are usually made up of contrasting colors such as green/yellow or purplish-blue/white.
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