Classifying bivalve larvae using shell pigments identified by Raman spectroscopy.

Because bivalve larvae are difficult to identify using morphology alone, the use of Raman spectra to distinguish species could aid classification of larvae collected from the field. Raman spectra from shells of bivalve larvae exhibit bands that correspond to polyene pigments. This study determined if the types of shell pigments observed in different species could be unique enough to differentiate larvae using chemotaxonomic methods and cluster analysis. We collected Raman spectra at three wavelengths from 25 samples of bivalve larvae representing 16 species and four taxonomic orders. Grouping spectra within general categories based on order/family relationships successfully classified larvae with cross-validation accuracies ≥92% for at least one wavelength or for all wavelengths combined. Classifications to species were more difficult, but cross-validation accuracies above 86% were observed for 7 out of 14 species when tested using species groups within orders/families at 785 nm. The accuracy of the approach likely depends on the composition of species in a sample and the species of interest. For example, high classification accuracies (85-98%) for distinguishing spectra from Crassostrea virginica larvae were achieved with a set of bivalve larvae occurring in the Choptank River in the Chesapeake Bay, USA, whereas as lower accuracies (70-92%) were found for a set of C. virginica larvae endemic to the Northeast, USA. In certain systems, use of Raman spectra appears to be a promising method for assessing the presence of certain bivalves in field samples and for validating high-throughput image analysis systems for larval bivalve studies.

Qualitative and quantitative analysis of CO2 and CH4 dissolved in water and seawater using laser Raman spectroscopy.

Laboratory experiments have been performed using laser Raman spectroscopy to analyze carbon dioxide (CO(2)) and methane (CH(4)) dissolved in water and seawater. Dissolved CO(2) is characterized by bands at approximately 1275 and 1382 Deltacm(-1). Dissolved CH(4) is characterized by a dominant band at approximately 2911 Deltacm(-1). The laboratory instrumentation used for this work is equivalent to the sea-going Raman instrument, DORISS (Deep Ocean Raman In Situ Spectrometer). Limits of quantification and calibration curves were determined for each species. The limits of quantification are approximately 10 mM for CO(2) and approximately 4 mM for CH(4). A ratio technique is used to obtain quantitative information from Raman spectra: the gas bands are referenced to the O-H stretching band of water. The calibration curves relating band height ratios to gas concentration are linear and valid for a range of temperatures, pressures, and salinities. Current instrumentation is capable of measuring the highest dissolved gas concentration observed in end-member hydrothermal fluids. Further development work is needed to improve sensitivity and optimize operational configurations.