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More about Corals

Diploria sp. visited by a yellow tropical fish

Recent reef-building corals in the Caribbean are related to some of the fossil corals that you may see around the Austin area.  The large 'brain-like' coral in this underwater shot is Diploria sp., a member of the family Faviidae.  The fossil specimen shown below is a member of the same family.


Taxon:   Favia texana
Horizon:  Dessau Formation
Age:  Upper Cretaceous
Locality:  Travis County

Some species of the genus Favia are still extant (living) today. It is unclear whether the fossil Favia were reef builders.  Certainly the reefs around Pilot Knob were very small!

Favia texana

Montastrea in the Flower Gardens

Coral reefs still exist not far from Texas. The platy coral, Montastrea sp., is part of the Flower Gardens in the Gulf of Mexico.


Corals reproduce by two methods: asexually by budding, in which one polyp splits to become two,  and sexually by releasing sperm and eggs  into the water column. Asexual budding creates new growth immediately adjacent to the original colony.  Sexual reproduction is shown below, with a synchronized release of sperm and eggs by a species of Montastrea.

M. faveolata releasing sperm and eggs (F.J.Viola)

Reef-building corals are also home to many other organisms.  The most important symbionts are the zooxanthellae shown to the right.  These micro-organisms live in the tissues of the coral animal, and use sunlight to create oxygen and carbohydrate from the carbon dioxide released by the coral.  The coral uses these products to grow, releasing even more carbon dioxide.  This process allows the coral to grow much faster than it could without the help of these symbionts.

Zooxanthellae (P. Dustan)
Christmas tree worms, Rainbow Gardens, Bahamas (J.Lang)

Many other organisms make their homes in the coral reefs.  The Christmas-tree worms (Spirobranchus sp.) in this image are living on the surface of a Diploria coral.

This specimen of Diploria was added to the NPL collection in the 1930's, and may have came from the Florida Keys.  Even on the now dead coral there is evidence of other life.  The holes visible on the enlarged portion below were probably made by a boring sponge or, in the caes of the larger holes, a boring bivalve.  On the underside one can find the remains of  an array of worm tubes, algae and foraminifera.
Diploria sp. - compare it to the living at the top of the page!

This enlargement  allows you to pick out the holes bored by sponges

The underside shows a thriving community of worms, algae, and foraminfera


 

 

Frequently used abbreviations: NPL  Non-vertebrate Paleontology Laboratory | TNSC Texas Natural Science Center | UTDGS Department of Geological Sciences | BEG  Bureau of Economic Geology | VPL Vertebrate Paleontology Laboratory | JSG  Jackson School of Geosciences | SUPPORT | VOLUNTEER | GLOSSARY


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