Abstract
Southwest Florida's oyster reefs have been integral to its estuarine ecology since the mid Holocene. Though Crassostrea virginica has not been commercially harvested since European colonization, pre-Columbian, Calusa Native Americans were significant users of the oyster, accumulating middens between 2000 BC to approximately AD 1550, while existing in large populations beginning in early AD. A conservation paleobiological study of oysters from archaeological deposits and modern reefs within Estero Bay (EB) and Pine Island Sound (PIS) was undertaken to determine if oyster productivity has changed due to aboriginal overharvesting. Archaeological samples include those from: (1) the Late Archaic of Useppa and Calusa Islands (PIS), early in Calusa history; and (2) Caloosahatchee I, II, and IV of Mound Key (ES) and Pineland (PIS), peak middle Calusa history. Oyster death assemblages from modern reefs neighboring each archaeological site were studied for comparison. Oyster convex (left) and cap (right) valve lengths and widths were measured; a subsample of convex valves from each sample was sectioned to count ligament pit growth lines and served as a proxy for oyster age and growth rate. Finally, the biologic taphonomic grade was scored for the interior valve surface for all samples and its variability compared; biologic taphonomic grade should be near pristine for oysters collected live for consumption. All archaeological samples exhibit significantly better and near pristine taphonomic grades when compared to modern assemblages, confirming oysters were harvested for food, rather than as just mound-building clutch. Convex valve length decreased significantly from Late Archaic to Caloosahatchee time, while modern assemblages were statistically indistinguishable from Late Archaic collections. The Caloosahatchee samples span 4 climatic intervals (Roman Warm, Vandal Minimum, Medieval Warm, and Little Ice Age), suggesting climatic change was not responsible for the shift in productivity. Results support the hypothesis of overharvesting during middle Calusa time, suggest modern oyster populations retain the capacity for large growth, and indicate that aboriginal activity and more recent effects of watershed management have not resulted in a permanent microevolutionary population shift.