How corals made rocks through the ages.

Jeana L Drake,Paul G Falkowski,Tali Mass,Jarosław Stolarski,Bas Van De Schootbrugge,Stanislas Von Euw

doi:10.1111/gcb.14912

Abstract

Hard, or stony, corals make rocks that can, on geological time scales, lead to the formation of massive reefs in shallow tropical and subtropical seas. In both historical and contemporary oceans, reef-building corals retain information about the marine environment in their skeletons, which is an organic-inorganic composite material. The elemental and isotopic composition of their skeletons is frequently used to reconstruct the environmental history of Earth's oceans over time, including temperature, pH, and salinity. Interpretation of this information requires knowledge of how the organisms formed their skeletons. The basic mechanism of formation of calcium carbonate skeleton in stony corals has been studied for decades. While some researchers consider coral skeletons as mainly passive recorders of ocean conditions, it has become increasingly clear that biological processes play key roles in the biomineralization mechanism. Understanding the role of the animal in living stony coral biomineralization and how it evolved has profound implications for interpreting environmental signatures in fossil corals to understand past ocean conditions. Here we review historical hypotheses and discuss the present understanding of how corals evolved and how their skeletons changed over geological time. We specifically explain how biological processes, particularly those occurring at the subcellular level, critically control the formation of calcium carbonate structures. We examine the different models that address the current debate including the tissue-skeleton interface, skeletal organic matrix, and biomineralization pathways. Finally, we consider how understanding the biological control of coral biomineralization is critical to informing future models of coral vulnerability to inevitable global change, particularly increasing ocean acidification.

Highlights

Indigenous peoples have used coral reef resources for tens of thousands of years (Kirch, 2017) and coral fossils were known in Nicolaus Steno’s time(Rosenberg, 2009), coral reefs were first brought to wider European knowledge by accident, at 11PM on 11 June 1770, when Lieutenant James Cook’s ship, HM Bark Endeavour, “bumped” and ran aground on the Great Barrier Reef off the northeast coast of Australia (Cook, 1770)
Nano-SIMS reveals that intracellular sites of concentrated calcium co-locate with aspartic acid-rich regions of the cell, such as those contained in highly acidic proteins later retained in coral skeleton (Mass, Drake, et al, 2017)
(the lowest Mg/Ca in the Phanerozoic) did not dictate the CaCO3 polymorph change in skeletons 499 of corals that remained aragonitic through their entire fossil record (Janiszewska, Mazur, Escrig, Meibom, & Stolarski, 2017). These observations suggest that the skeletal formation process in corals is strongly physiologically controlled and these organisms are capable of biomineralization using the same mineral in geochemically altered sea conditions

Summary

Introduction

Indigenous peoples have used coral reef resources for tens of thousands of years (Kirch, 2017) and coral fossils were known in Nicolaus Steno’s time (the late 17th century)(Rosenberg, 2009), coral reefs were first brought to wider European knowledge by accident, at 11PM on 11 June 1770, when Lieutenant James Cook’s ship, HM Bark Endeavour, “bumped” and ran aground on the Great Barrier Reef off the northeast coast of Australia (Cook, 1770). These extra-crystalline phases 238 are not considered as the direct result of the coral biomineralization process since their presence could have different origins such as a mineral deposition due to the activity of boring organisms present within the skeleton (Macintyre & Towe, 1976), diagenetic alteration of the primary skeletal deposits (Frankowiak et al, 2013), secondary deposition of calcareous matter (Cusack et al, 2008; Dalbeck et al, 2011; Enmar et al, 2000), or even the result of an inorganic precipitation upon drying.

Results

Conclusion