Abstract
Barrier islands and crassostrcid oyster reefs arc 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 reefs 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 study. Three transects were established on each reef. At three-meter intervals along each transect twenty-five oysters were collected from a one-square meter quadrant. For each shell collected, height, width, valve thickness, and percent of shell surface experiencing encrustation, biocrosion, and margin loss were measured. The architecture of oyster clumps was described by measuring clump height and circumference. Sediment samples were also collected from each reef and subjected to grain size analysis. No pattern was discemablc 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 favoring larger and thicker shells. There is also a significantly higher percent bioerosion and margin loss on the high energy reefs compared to the low energy reefs, possibly indicating a longer period of exposure in the taphonomically active zone. Percent encrustation and sediment grain size distribution are not shown to be distinguishing factors along an environmental gradient. Valve morphology, percent bioerosion, and percent margin loss could aid in determining paleoenvironmental conditions of historical oyster reefs.