More on Corals from This Week’s Science Magazine

A World with Corals: What Will It Take?

………..The measures required to limit climate change can seem an eternity away to coastal communities left to deal with the consequences. Yet, since the 1997-98 mass bleaching–an unforgiving global event that destroyed 16% of the world’s coral reefs–practitioners and scientists have worked to identify meaningful actions that can promote reef survival in the face of climate change………

Although the current greenhouse trajectory is disastrous for coral reefs and the millions of people who depend on them for survival, we should not be lulled into accepting a world without corals. Only by imagining a world with corals will we build the resolve to solve the challenges ahead. We must avoid the “game over” syndrome and marshall the financial, political, and technical resources to stabilize the climate and implement effective reef management with unprecedented urgency.

Rethinking Coral Composition

Modern coral reefs are built primarily by scleractinian corals, which arose in the Triassic after the Permian extinction. Today, all of these corals form skeletons of aragonite, and this composition has been thought to be typical of fossil scleractinians as well. Stolarski et al. (p. 92) now have identified a Cretaceous scleractinian coral with a primary calcite skeleton. The fine preservation of internal structures and the Mg and Sr chemistry show that the calcite is primary, not diagenetic. This result tightens the evolutionary connection between these corals and rugose corals, which formed calcite skeletons but were eliminated in the Permian extinction. These results suggest that corals may be able to alter their biochemistry in response to changes in seawater chemistry.

A Cretaceous Scleractinian Coral with a Calcitic Skeleton

Jarosaw Stolarski,1* Anders Meibom,2 Radosaw Przenioso,3 Maciej Mazur4
It has been generally thought that scleractinian corals form purely aragonitic skeletons. We show that a well-preserved fossil coral, Coelosmilia sp. from the Upper Cretaceous (about 70 million years ago), has preserved skeletal structural features identical to those observed in present-day scleractinians. However, the skeleton of Coelosmilia sp. is entirely calcitic. Its fine-scale structure and chemistry indicate that the calcite is primary and did not form from the diagenetic alteration of aragonite. This result implies that corals, like other groups of marine, calcium carbonate–producing organisms, can form skeletons of different carbonate polymorphs.