Non-destructive raman spectroscopic determination of freshwater mollusk composition, growth, and damage repair

Abstract

Increased acidification of aquatic habitats due to climate change is damaging mollusks. Non-destructive methods for analysis are necessary to study these endangered species. We analyzed five Unionidae gastropods using Raman spectroscopy. Shells were primarily composed of aragonite, a polymorph of calcium carbonate found in shell microstructure. Lattice mode Raman peaks from vaterite, a thought to be rare polymorph of calcium carbonate, were identified in each mollusk. Vaterite is present in mollusks at instances of shell damage and subsequent repair. We demonstrate that Raman spectroscopy is sensitive to vaterite, and it may not be as rare as previously thought. We also collected Raman spectra across the interior of Lampsillis fasciola. This data was analyzed through multivariate analysis, combining Principal Component Analysis with Linear Discriminant Analysis (PCA-LDA). Results of PCA-LDA correlate with growth of the mollusks, demonstrating that Raman spectroscopy combined with multivariate analysis could be used to monitor shell growth.