An analysis of bivalve larval shell pigments using micro-Raman spectroscopy

Micro-Raman spectroscopy has been used on adult bivalve shells to investigate organic and inorganic shell components but has not yet been applied to bivalve larvae. It is known that the organic matrix of larval shells contains pigments, but less is known about the presence or source of these molecules in larvae. We investigated Raman spectra of seven species of bivalve larvae to assess the types of pigments present in shells of each species and how the ratio of inorganic : organic material changes in a dorso-ventral direction. In laboratory experiments, we reared larvae of three clam species in waters containing different organic signatures to determine if larvae incorporated compounds from source waters into their shells. We found differences in spectra and pigments between most species but found less intraspecific differences. A neural network classifier for Raman spectra classified five out of seven species with greater than 85% accuracy. There were slight differences between the amount and type of pigment present along the shell, with the prodissoconch I and shell margin areas being the most variable. Raman spectra of 1-day-old larvae were found to be differentiable when larvae were reared in waters with different organic signatures. With micro-Raman spectroscopy, it may be possible to identify some unknown species in the wild and trace their natal origins, which could enhance identification accuracy of bivalve larvae and ultimately aid management and restoration efforts. Copyright (c) 2014 John Wiley & Sons, Ltd.