Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sea change: Skeletons of ancient corals different from today’s

10.11.2004


A Johns Hopkins University graduate student may have solved a problem that has been baffling marine biologists and paleontologists for years: Why do coral reefs disappear from the fossil record during the beginning of the Cretaceous period -- 120 million years ago -- only to reappear after its end 35 million years ago?



The possible answer: Ancient seawater’s low magnesium-to-calcium ratio during this interval made it difficult for the marine animals -- which build their skeletons from a mineral called aragonite calcium carbonate -- to grow and flourish into vast reefs. That left few to end up in the fossil record, posits doctoral candidate Justin Ries and his advisor Steven Stanley, professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at the university’s Zanvyl Krieger School of Arts and Sciences.

"Scientists have grappled with this question for years, and my research shows that the answer is that the chemistry of Cretaceous seawater did not support the secretion of the aragonite mineral from which corals construct their skeleton," said Ries, who will present his research on Nov. 10 at the 116th annual meeting of The Geological Society in Denver. "What’s more, my experiments suggest that corals from the Cretaceous period almost certainly built at least part of their skeletons from calcite. This is groundbreaking, because it was previously believed that organisms do not generally change their skeletal mineralogy over time. Now we know that they do."


Ries spent two months growing three species of modern Scleractinian corals (the major reef-building corals in today’s seas) in seawater formulated at six different chemical ratios that have existed throughout the geologic history of corals. He created this seawater "from scratch" according to recipes provided by earth and planetary sciences Professor Lawrence Hardie, who recently discovered that the magnesium-to-calcium molecular ratio of seawater has oscillated between 1.0 and 5.2 over the past 540 million years due to chemical reaction between rising magma and seawater brine along various parts of the ocean floor.

"The artificial seawaters were created by adding different concentrations of salts as calculated by Lawrence Hardie," Ries said. "I specifically wanted to test how modern corals respond to the ancient levels of magnesium and calcium because these chemicals, along with carbon and oxygen, are the building blocks of their skeletons. More important, however, is that the ratio of these two chemicals determines whether the aragonite or calcite mineral will form."

Into 10-gallon tanks filled with these mixtures went coral fragments replete with colonies of polyps -- tiny animals, a few millimeters in size, from which larger corals and, eventually, reefs grow. Ries prepared the polyps for the experiment by having them spend a one-month "adjustment period" in tanks filled with modern seawater. Gradually, Ries adjusted the tanks’ chemistry until their contents were in line with the prescribed "ancient" seawater chemistries.

"To prevent the corals from experiencing chemical shock in the unfamiliar seawaters, I learned that they must be acclimated gradually, in stages," Ries said. "This was actually one of the most challenging aspects of the project. There were many failed attempts before I was able to keep the corals alive, so that I could observe their growth and calcification in the ancient seawaters."

The corals were grown under special lights called "PowerCompacts" which simulated true daylight by emitting a wavelength commensurate to sunrise and sunset in the morning and evening, as well as normal sunlight during the rest of the day. Ries fed the growing corals with plankton particles, and monitored each tank’s pH level -- and level of chemicals such as strontium, iodine and manganese, as well as vitamins -- several times a week. Ries credits his experiments with leading to "two very important discoveries about corals."

First, the skeletons of the corals cultivated in the ancient seawaters had a different mineral composition from those grown in modern seawater. Those in the so-called Cretaceous seawater began building skeletons of 35 percent calcite mineral, as opposed to modern corals, which built them from 100 percent aragonite. This suggests that the skeletons of corals have been changing along with seawater throughout the geologic past. "This is astounding, given that most scientists have long believed that the mineral composition of a group of organisms’ skeletons is fixed over time," Ries said.

Secondly, the experiment was important because it proved corals cultivated in Cretaceous seawater grew more slowly than their counterparts raised in modern seawater. "This solves, experimentally, the longstanding question of why the Scleratinian corals stopped making reefs during the Cretaceous: because the low magnesium/calcium ratios in the oceans at that time inhibited the growth of the aragonite mineral that they used to build their skeletons," Ries said.

Lisa DeNike | EurekAlert!
Further information:
http://www.jhu.edu

More articles from Earth Sciences:

nachricht Heidelberg Researchers Study Unique Underwater Stalactites
24.11.2017 | Universität Heidelberg

nachricht Lightning, with a chance of antimatter
24.11.2017 | Kyoto University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New proton record: Researchers measure magnetic moment with greatest possible precision

High-precision measurement of the g-factor eleven times more precise than before / Results indicate a strong similarity between protons and antiprotons

The magnetic moment of an individual proton is inconceivably small, but can still be quantified. The basis for undertaking this measurement was laid over ten...

Im Focus: Frictional Heat Powers Hydrothermal Activity on Enceladus

Computer simulation shows how the icy moon heats water in a porous rock core

Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

IceCube experiment finds Earth can block high-energy particles from nuclear reactions

24.11.2017 | Physics and Astronomy

A 'half-hearted' solution to one-sided heart failure

24.11.2017 | Health and Medicine

Heidelberg Researchers Study Unique Underwater Stalactites

24.11.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>