2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 130-15
Presentation Time: 9:00 AM-6:30 PM


LONG, Brooke L., Geology and Geological Engineering, South Dakota School of Mines and Technology, 501 E Saint Joseph Street, Rapid City, SD 57701, ANDERSON, Laurie C., Geology and Geological Engineering, South Dakota School of Mines and Technology, 501 East St. Joseph St, Rapid City, SD 57702 and ENGEL, Annette Summers, Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996, brooke.long@mines.sdsmt.edu

Lucinidae are the most taxonomically diverse group of chemosymbiotic bivalves, as well as the most common infaunal bivalves found in shallow-water seagrass environments. Determining associations of environmental factors with lucinid morphology would allow assessment of past paleoenvironments for both historical collections and fossil assemblages. In this study, geometric morphometrics was used to examine the morphologic variability of the lucinid Stewartia floridana in seagrass-covered and bare sand in a relatively stable coastal system near Bokeelia, Florida. Five 50-m sampling transects over a 60-m distance were established along the shoreline, each starting five meters from the shoreline and extending out seaward; lucinid specimens and porewater geochemistry were sampled in both seagrass and unvegetated sands along these transects. This fine-scale sampling scheme ensured that specimens collected in both seagrass and unvegetated sands have experienced the same large-scale environmental factors. Spatial stability of seagrass beds over the past ten years was confirmed through geospatial analysis. We estimate S. floridana’s life span to be <10 years so that the 282 live and dead-articulated specimens used should have inhabited similar sediment conditions through their lives. A landmark configuration for geometric morphometrics included quantifying the size, shape, and orientation of the inhalant channel, muscles scars, pallial line, and hinge. Ordination of groups reveal that habitat for S. floridana is not related to morphology, with individuals from seagrass and unvegetated areas not differing significantly in shape, and with low classification accuracy based on bootstrapping and jackknifing techniques (<60%). Further, although there is an allometric trend in shape, size is unrelated to vegetative cover. These results indicate that morphology is consistent between vegetated and unvegetated patches within the seagrass habitat. Porewater geochemistry, however, does not show a simple relationship with seagrass patches and these variables need to be tested for correlation with lucinid morphology.