Investigating marine bio-calcification mechanisms in a changing ocean with in vivo and high-resolution ex vivo Raman spectroscopy.

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio-calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non-classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high-resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio-calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.