Yellow finger coral

Madracis auretenra

''Madracis auretenra'', commonly known as the yellow finger coral or yellow pencil coral, is a colonial species of stony coral in the family Astrocoeniidae. It is a fairly common species and is found in the Caribbean Sea and western Atlantic Ocean. At one time this species was not recognised, but it was split from ''Madracis mirabilis'' on the grounds of morphology and depth range.
Yellow Pencil Coral Sep 11, 2017. 1000 Steps, Bonaire.
A mini-prairie of fluffy coral with some happy bicolor damselfishes hovering on top.
Colonies of this coral are branching with densely packed fingers, each of which is relatively fragile. Colonies may cover several square metres. Colour is pale yellow, and pale polyps are commonly extended in daytime as well as at night, giving a fuzzy appearance to the colonies. Calices have 10 septa. Caribbean Netherlands,Geotagged,Madracis auretenra,Summer


''Madracis auretenra'' forms hemispherical clumps that can be a metre or more across. Each colony is formed of densely packed, cylindrical branches with blunt, finger-like tips. In fore-reef habitats the branches are slender but in back-reef and lagoon habitats they are more robust and the clumps are larger. The hard skeletal material of which the colony is built is in most coral species covered by a thin layer of living tissue, the coenosarc. ''M. auretenra'' is unusual in this respect because, as the coral grows, the coenosarc progressively dies back on the lower parts of the branches leaving the skeleton bare, and only the tips of the branches are covered with living tissue. The corallites are from 1.1 to 1.6 mm in diameter and have at least ten septa. This coral is bright yellow.


''Madracis auretenra'' is a zooxanthellate coral, housing symbiotic single-celled protists within its tissues. These provide the products of photosynthesis to the coral and use some of the coral's waste products. To supplement this food supply, the coral polyps spread their tentacles to catch zooplankton, feeding mostly on the larvae of crustaceans, polychaete worms and arrow worms.

''M. auretenra'' is a hermaphrodite; individual colonies contain both male and female gonads. Liberation of gametes into the sea is linked to the phase of the moon and other factors. After fertilisation, the planula larvae form part of the plankton and eventually settle on the seabed and undergo metamorphosis into polyps. In some instances, ''M. auretenra'' has been observed to retain the gametes on its mesenteries and pseudo-brood the larvae briefly before liberating them into the sea.

''M. auretenra'' also reproduces readily by fragmentation, a form of asexual reproduction. Even quite small fragments of the coral are able to survive and grow into new colonies; survival rates in trial studies varied between 29 and 81%, with the rates being highest in fore-reef environments and lowest in lagoons where there were higher levels of sedimentation.

''M. auretenra'' has been used as a study organism to predict the effects of ocean acidification on corals. By manipulating the composition of modified sea water in which the corals were kept, it has been shown that the carbonate or aragonite concentration of the water, the factor usually considered as important predictors, was less relevant than the bicarbonate concentration.


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SpeciesM. auretenra