TAPHONOMIC ANALYSIS OF OYSTER SHELLS: A TECHNIQUE TO INTERPRET THE HOLOCENE HISTORY OF COASTAL ENVIRONMENTAL CHANGE

Barrier islands and crassostreid oyster reefs are important components of estuarine systems along the Gulf of Mexico and the Atlantic coast. The development of crassostreid reefs is critical to coastal progradation, and therefore estuarine development. Oyster boundstones are often used as indicators of sea level in the stratigraphic record. However, because oysters thrive across broad estuarine gradients in both salinity and energy, it is often difficult to refine a reef's paleoenvironmental position. The purpose of this research is to compare the physical and biologic taphonomic and architectural characteristics on modern Crassostrea virginica reefs, relative to an environmental gradient with respect to salinity and energy, with the hope of better interpreting the history of estuarine development during changes in sea-level rise rates. A better understanding of coastal environmental history should result, thereby improving future management and restoration efforts. Three high energy and three low energy reefs in the Ten Thousand Islands of Southwest Florida were selected for this study. Three transects were set up on each reef. At three-meter intervals along each transect twenty-five oysters were collected from a one-square meter quadrat. For each shell collected, height, width, valve thickness, and percent of shell surface experiencing encrustation, bioerosion, and margin loss were measured. The architecture of oyster clumps was described by measuring clump height and circumference. No pattern was discernable from clump architecture, and the size of clumps varied throughout the six reefs. The high energy reefs' valves were longer, wider, and thicker on average. This may be due to a difference in population structure, growth rates or taphonomic bias. There is also a significantly higher percent of bioerosion and margin loss on the high energy reefs compared to the low energy reefs, indicating a longer period of exposure in the taphonomically active zone. Encrustation is not shown to be a distinguishing taphonomic character. No apparent distinction between the composition of bioeroders exists between low energy and high energy reefs.