Morphological Response of the Bivalve Genus Chione to Regional Environmental Variation and Anthropogenic Change

Recent research has demonstrated the utility of molluscan subfossil assemblages for diagnosing anthropogenic changes to coastal marine environments. While this work has focused mainly on changes through time in species compositions and relative abundances, species morphologies may be impacted as well. Here, we present a preliminary investigation of morphological variability in the prolific venerid bivalve Chione cancellata and the closely related form, C. elevata. The goal of this study was to quantify the extent of morphological variation, if any, in Chione as a function of environment and geography, and to determine whether a compositional change over a two-decade interval in the molluscan biota of a locality in St. Croix, U.S. Virgin Islands was accompanied by a change in the morphology of C. cancellata.

For this pilot study, we focused on samples collected during previous investigations in Smuggler's Cove and Salt River Bay along the coast of St. Croix. Individuals were digitally imaged, and morphological data were collected from landmark points corresponding to the beak, hinge area, muscle scars, and exterior outline of each shell. Multivariate techniques, including Generalized Procrustes Analysis, were applied to examine Chione morphology through space and time.

Results of our analyses to date point to significant changes in landmark positions in relation to geography and environment, even between samples from sites less than a kilometer apart where ambient conditions are also demonstrably different. Furthermore, within Smuggler's Cove, there is evidence of significant morphological differences among specimens collected two decades apart, although this result should be viewed as preliminary, pending further analyses. What is clear, however, is that Chione has a strong propensity to vary morphologically even over limited spatial scales, and we will continue to analyze the nature of this variation throughout a broader study region that encompasses the western Caribbean, the Bahamas, and Florida.