Madracis auretenra
A bright yellow stony coral split from Madracis mirabilis.
Madracis auretenra, called the yellow finger coral or yellow pencil coral, is a colonial stony coral belonging to the family Pocilloporidae. It is fairly common and lives in the Caribbean Sea and western Atlantic Ocean. This species was not originally recognized; it was separated from *Madracis mirabilis* due to differences in form and the depths where it grows.
The species was formally described in 2007 by Locke, Weil, and Coates. They distinguished it from *Madracis mirabilis*, a deep-water coral, by its thin, branching, tree-like shape and its depth range of 1 to 60 meters. Other unique traits include bare skeletal areas at the base lacking living tissue, a fairly smooth surface between the polyps, a clear line of spines between the corallites, and the absence of secondary septa in the tightly packed corallites. The authors noted that many earlier studies on *Madracis mirabilis* might need to recheck which species they were actually studying.
Colonies of *M. auretenra* form hemispherical clumps that can reach over a meter across. They are made of densely packed, cylindrical branches with blunt, finger-like tips. In fore-reef areas the branches are slender, but in back-reef and lagoon habitats they are thicker and the clumps are larger. Unlike most stony corals, the living tissue covering the skeleton dies back on the lower parts of the branches as the coral grows, leaving bare skeleton, so only the branch tips stay covered. The corallites measure 1.1 to 1.6 millimeters across and have at least ten septa. The coral is bright yellow.
This coral is zooxanthellate, hosting symbiotic single-celled protists in its tissues that provide products from photosynthesis and use some of the coral’s waste. To supplement this, the polyps extend their tentacles to catch zooplankton, mainly feeding on larvae of crustaceans, polychaete worms, and arrow worms. *M. auretenra* is a hermaphrodite, with each colony containing both male and female gonads. The release of gametes into the water is tied to the moon’s phase and other factors. After fertilization, the planula larvae drift as plankton before settling on the seabed and turning into polyps. In some cases, the coral holds the gametes on its mesenteries and briefly pseudo-broods the larvae before releasing them. The coral also reproduces easily by fragmentation, a form of asexual reproduction.
Quick Facts
- Taxon
- Madracis auretenra
Facts from the source article.
Lore & Background
Madracis auretenra was erected as a new species in 2007 by Locke, Weil & Coates, who distinguished it from Madracis mirabilis (a deep-water species) based on its thin-branched, dendritic structure and its depth range of 1 to 60 m. Other distinguishing features include base skeletal structures devoid of living tissue, a fairly smooth coenosteum, a distinct line of spines between corallites, and the absence of secondary septa in closely spaced corallites. The authors noted that many recent studies on Madracis mirabilis sensu Wells would need to reconsider the identities of their study organisms.
The coral forms hemispherical clumps of densely packed, cylindrical branches with blunt, finger-like tips. In fore-reef habitats branches are slender, while in back-reef and lagoon habitats they are more robust and clumps larger. Unusually, as the coral grows, the coenosarc (living tissue) progressively dies back on lower parts of branches, leaving only the tips covered with living tissue. The corallites have at least ten septa. The coral is bright yellow.
Ecologically, Madracis auretenra is zooxanthellate, housing symbiotic protists that provide photosynthetic products. It supplements its diet by catching zooplankton, primarily larvae of crustaceans, polychaete worms, and arrow worms. It is a hermaphrodite, with colonies containing both male and female gonads. Gamete liberation is linked to the moon phase; after fertilization, planula larvae form plankton and eventually settle. In some instances, gametes are retained on mesenteries and pseudo-brooded briefly before release. The coral also reproduces readily by fragmentation, with survival rates of fragments ranging from 29 to 81%, highest in fore-reef environments and lowest in lagoons with higher sedimentation.
Reader's Guide
Madracis auretenra is significant as a species that was formally recognized only in 2007, when it was split from Madracis mirabilis based on morphology and depth range. This taxonomic revision prompted a call for researchers to re-evaluate previous studies that had used the name Madracis mirabilis sensu Wells. The species is notable for its unusual growth habit: the living tissue dies back on lower branches, leaving bare skeleton, a trait that distinguishes it from many other stony corals. Its bright yellow coloration and finger-like branches make it visually distinctive.
Ecologically, Madracis auretenra has been used as a study organism to predict the effects of ocean acidification on corals. Experimental manipulation of seawater composition showed that bicarbonate concentration was a more relevant predictor of coral health than carbonate or aragonite concentration, the factors usually considered important. This finding has implications for understanding how corals may respond to changing ocean chemistry.
The species' ability to reproduce both sexually (with gamete release linked to lunar cycles) and asexually via fragmentation contributes to its persistence. Fragmentation survival rates vary by environment, being highest in fore-reef areas. Its role as a zooxanthellate coral and its feeding on zooplankton larvae place it within the broader reef ecosystem dynamics. The article does not discuss conservation status or broader legacy beyond these points.
Did You Know?
- Madracis auretenra was split from Madracis mirabilis in 2007 by Locke, Weil & Coates.
- It reproduces both sexually (with gamete release linked to the moon phase) and asexually by fragmentation.
- Studies using this coral showed that bicarbonate concentration was more relevant than carbonate or aragonite for predicting ocean acidification effects.
Frequently Asked Questions
Who is Madracis auretenra?
Madracis auretenra is a colonial stony coral in the family Pocilloporidae, best known by its common names yellow finger coral and yellow pencil coral. It is a fairly widespread species throughout the Caribbean Sea and the western Atlantic Ocean.
What does Madracis auretenra look like?
The colony grows in a thin, branching, tree-like form and is instantly recognizable by its vivid, bright yellow color. Individual corallites are quite small, measuring only about 1.1 to 1.6 mm in diameter, which gives the whole structure a delicate, pencil-thin appearance.
Where can you find Madracis auretenra and how deep does it grow?
This species ranges from the shallow surface down to roughly 60 meters (about 197 feet) in Caribbean and western Atlantic waters. That broad depth span is actually one of the main traits that separates it from the deeper-water relative Madracis mirabilis.
When and by whom was Madracis auretenra officially described?
Researchers Locke, Weil, and Coates formally named and described the species in 2007. They split it off from Madracis mirabilis after observing clear differences in colony shape and the depth zones where each typically occurs.
Why is Madracis auretenra important to coral enthusiasts?
It serves as a great example of how Pocilloporidae taxonomy continues to be refined, since it was only recognized as a distinct species in the mid-2000s. Its eye-catching yellow color and accessible depth range also make it a favorite subject for reef divers and underwater photographers in the Caribbean.
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