MORPHOLOGIC DIVERGENCE BETWEEN LIFE AND DEATH ASSEMBLAGES OF STEWARTIA FLORIDANA (BIVALVIA, LUCINIDAE) FROM PINE ISLAND, FLORIDA

Comparisons of life and death assemblages provide valuable baselines for interpreting ecologic and evolutionary patterns in fossil assemblages. In these studies, intraspecific morphologic patterns are less well characterized than diversity and abundance. We compared intraspecific morphologic variation in live and co-occurring dead-articulated individuals of the lucinid Stewartia floridana to test whether a correlation between environment and morphology in live individuals is preserved in co-occurring dead specimens. Individuals were collected from shallow subtidal sediment off Pine Island, FL, along transects intersecting sand and seagrass patches of varying temporal stability. Geometric morphometric data indicated that shapes of live S. floridana varied along a gradient related to the presence and stability of seagrass beds. We tested whether this trend was preserved in co-occurring death assemblages that were both spatially (articulated valves are less likely to have undergone extensive post-mortem transport) and temporally (regional sea level curves indicate inundation of the area <4 kyr) constrained. Our results indicate that death assemblages neither show the same morphologic trend or a temporally/spatially-averaged scatter likely derived from live specimens. Instead, live and dead-articulated S. floridana were morphologically distinct. This distinction does is not caused by allometry, as the size of live and dead-articulated specimens are not significantly different and each group follows a distinct allometric trend. Further, morphologic differences observed likely are not due to differences in digitization accuracy or precision caused by taphonomic alteration. Assuming that time-averaged death assemblages represent the morphology typical for S. floridana at this locality historically, live specimens are outliers possibly representing distinct environmental conditions that developed within the last decade, as live individuals are <7 years old.