Orbicella franksi
A near-threatened colonial stony coral of the Caribbean.
Orbicella franksi, called boulder star coral, is a stony coral that forms colonies and belongs to the family Merulinidae. It lives in the shallow waters of the Caribbean Sea, Gulf of Mexico, Bahamas, Bermuda, and Florida, and the International Union for Conservation of Nature lists it as near threatened.
Until recently, scientists considered this coral and Orbicella faveolata to be varieties of Orbicella annularis. Though they look very similar, studies reveal differences in corallite structure, life history, allozymes, and distribution. All three species in this complex were once placed in the genus Montastraea.
Colonies of O. franksi typically grow as massive, uneven lumps, but they can also form plates or, in shady spots, encrusting sheets. Their color ranges from orange-brown to greenish-brown or greyish-brown, with the lump tips often pale or white. The corallites—the cups housing the polyps—are small, about 3.5 mm across. Unlike the closely related O. faveolata, which has evenly spaced corallites at its growing edges, this coral’s growing edges have both large and small corallites.
This species is native to the Caribbean Sea and Gulf of Mexico, including Florida, the Bahamas, and Bermuda. It commonly grows on fore reefs, where it can be the most abundant coral, and lives at depths from 5 to 50 meters, though it is usually found between 15 and 30 meters.
O. franksi appears more resistant to coral diseases than some related species, but it still suffers from coral plague, yellow-band disease, black band disease, and coral bleaching. Its main threats include climate change, ocean acidification, and reef habitat destruction. The IUCN has rated its conservation status as near threatened.
Quick Facts
- Taxon
- Orbicella franksi
Facts from the source article.
Lore & Background
Until recently, Orbicella franksi, along with Orbicella faveolata, was thought to be a variety of Orbicella annularis. There is very little morphological difference between them, but studies have shown differences in corallite structure, life history, allozymes and distribution. All three members of this species complex used to be placed in the genus Montastraea.
Colonies of Orbicella franksi usually form massive clumps with uneven surfaces, but sometimes form plates, and in shady positions may be encrusting. The general colour is orange-brown, greenish-brown or greyish-brown, but the extremities of the lumps are often pale or white. The corallites measure 3.5 mm across. The growing edges of this coral bear both large and small corallites, in contrast to the closely related Orbicella faveolata, which has regularly spaced corallites at its growing edges.
Orbicella franksi typically grows on fore reefs, where it may be the most common species of coral, and its depth range is 5 to 50 metres, though it is typically found at depths between 15 and 30 metres.
Reader's Guide
Orbicella franksi is notable for its role in the Orbicella species complex, having been historically confused with Orbicella annularis and Orbicella faveolata. Its distinction was established through studies of corallite structure, life history, allozymes and distribution, despite very little morphological difference. This coral is ecologically significant on Caribbean fore reefs, where it can be the most common species. Its conservation status as near-threatened reflects its vulnerability to climate change, ocean acidification and destruction of reef habitat. While it appears more resistant to coral diseases than some members of its genus, it remains susceptible to coral plague, yellow-band disease, black band disease and coral bleaching. The species' ability to form massive clumps, plates or encrusting growths depending on light conditions, and its distinctive growing-edge corallite pattern, help differentiate it from its close relatives. Its depth range of 5 to 50 metres, with typical occurrence between 15 and 30 metres, places it in a specific reef zone where it contributes to the structural complexity of Caribbean coral ecosystems.
Did You Know?
- Orbicella franksi was once thought to be a variety of Orbicella annularis.
- Its growing edges bear both large and small corallites, unlike the closely related Orbicella faveolata.
- It is listed as near-threatened by the International Union for Conservation of Nature.
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