tinents, we would see that these reefs were not ... Development and Death of Devonian (oral Reefs. (continued ... corals were killed during the mass extinction at ...
SAINT LOUIS UNIVERSITY
NOVEMBER 2002 .
Development and Death of Devonian (oral Reefs I
VOL.
MADRID CAMPUS
10 . N° 3
Something(s) to DO! wa'k to school in the moming and usually back horne in the evening, so I am very aware ofthe change ofthe seasons in Madrid.It is nothing like watehing the colors change in the Shenandoah va11ey,where the Appalachians undulate in vibrant waves of red, orange, and gold, but auturnn in Madrid has a certain charm of its own. I love walking up smaller streets where the greedy street sweepers don't sweep away the fallen leaves, and I can shuffle my feet up the sidewalk, kicking sprays of leaves like a little kid. And Retiro Park on the weekends is full ofhuge piles ofraked leaves just begging to be jumped in-although 1'11adrnit that wasn't what the Limpio Madrid (or the Green Man, as I like to ca11him) told me. I love how the sun looks orange and the sky turns amazing shades of pink and blue at sunset. I love putting on sweaters and scarves and bending my head into the crisp w in d . (page 6)
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magine we had a time machine on our Madrid campus, and we decided to go back 380 million years into the Devonian period. What would we see? A tropical sea with islands. On land, there would only be some shrubs, herbs, and insects-no marnmals or birds. The first amphibians would be beginning to creep onto the land.
However, the shallow tropical water at this time was full oflife. We would see plenty of coral reefs, with an overflowing abundance of corals, fish, and many other kinds of animals. And if we were able to go to other continents, we would see that these reefs were not restricted to Spain or Europe, but that they were spread over most parts ofthe Devonian world. (page 2)
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pain is a country characterized by its nightlife. Foreign visitors are usually surprised to see pubs and discos open on Thursdays at five in the moming. Nevertheless, for Spaniards, this is as normal as getting up for work every day. Lately, however, the Spanish government does not seem to approve of
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Development and Death of Devonian (oral Reefs (continued from first page)
In the middle of the Devonian period, the reefs were even more widespread than they are today. In addition, several of these reefs were huge. At first glance, the Devonian reefs would much resemble more recent coral reefs. But a eloser look would reveal that the animals building these reefs were remarkably different from the animals building recent coral reefs.
The stromatoporoids played a crucial role in the Devonian reefs. In the early Devonian period (about 400 million years ago), stromatoporoids were very scarce, and as a result the reefs were also scarce and small. I have recently investigated one ofthese few Early Devonian reefs located elose to Prague in the Czech Republic. I was surprised to recognize that this small reef was mainly built by corals and algae and that stromatoporoids only played a very sub-
In the Devonian reefs, the corals themselves play only a subordinate role. Beyond this fact, the Devonian corals are only the relatives, not the ancestors, of more recent corals. The last direct descendants of the Devonian corals were killed during the mass extinction at the end of the Permian period, 248 million years ago. The Devonian reefs were built mainly by an extinct group of colonial organisms called stromatoporoids. Their skeletons consisted of calcium carbonate and had the shape of layers, bulbs, or shrubs. Under the microscope, a three-dimensional network of pillars and plates becomes visible. Paleontologists like myself investigate this microscopic three-dimensional network in order to distinguish different species. For the past 150 years, what kind of organisms the stromatoporoids are has been highly disputed. In the 1970's, biologists found living animals with a similar skeleton in the Caribbean Sea. Thus, we know that the stromatoporoidsmust have been a kind ofsponge.
Reet
ordinate role-the
poroids were exterminated. Only deep-water corals were able to survive. The reef ecosystem needed a long time after the Frasnian/Famennian mass extinction event to recover from this shock. For a long time afterwards, reefs remained small and scarce, and corals were not important reef-builders. The first true coral reefs appeared again in the late Triassie period (about 215 million years ago), but after this it was a long way to the recent splendour of coral reefs. The reasons for the Frasnianl Famennian mass extinction are not elear. We know that this extinction event killed two-thirds of all species of marine organisms-the shallow marine ecosystems were especially hard-hit. Some of my colleagues hypothesize that the FrasnianlFamennian mass extinction was caused by the impact of a huge meteorite, but most facts suggest another explanation: for example, that this mass extinction was not a single event but a combination oftwo events that followed each other over 1-2 million years. Each of these events shows many similarities to smaller, less harmful events during the Devonian time.
Open sea
opposite of later Devonian reefs.
Did it depend on differences in the elimate? Or did the stromatoporoids after the Early Devonian time evolve in such a way that it enabled them to build these widespread and huge reefs? Nobody knows. Similarly mysterious is the end ofthe Devonian reefs: 368 million years ago, when the reefs had reached their maximum distribution, the so-called FrasnianIFamennian mass extinction wiped out the reefs totally. All reef-building corals and stromato-
Six years aga I developed a model to explain the FrasnianlFamennian mass extinction by sea-Ievel rises. Many questions, however, remain open. Nevertheless, two things become elear: first of all, coral reefs are very sensitive to environmental impacts. And second, our recent coral reefs are very precious. If they are destroyed, nature will need a very long time to build new reef ecosystems. Andreas May, Ph.D. Science and Engineering
