The How:
Once I have the samples back in the lab, I measure, dry, and weigh each part of the oyster (the top shell, meat, and bottom shell). Then comes the fun part. I use a small Dremel saw to cut the bottom shell in half along the hinge. This is when that calcein dye comes into play. When we stain the oysters with calcein, we are essentially making a date mark as the fluorescent dye is incorporated into their shells (see the image below). Think of this like looking at tree rings! We can take pictures of this stain, which allows us to determine the growth rate between each period of staining.
Once I have finished imaging the oysters, I can analyze them for their U/Ca ratios. I do so using a laser ablation inductively coupled mass spectrometer (LA-ICP-MS). This machine allows us to trace a path along the line of growth on the hinge of the oyster to analyze the chemical makeup of the shell. At my sample site, we are lucky to have such an instrument in place very close to the location of our oysters. Thus providing us a means of calibrating our U/Ca proxy.
Next week will wrap up this series with a discussion of next steps and the fabulous people who make this work possible.
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