Historical ecology of oysters - 2016

Introduction

             Oysters are synonymous with lowcountry culture, particularly in Charleston, SC.  They characterize the natural landscape by providing crucial habitats for native species, and act as a substantial commercial resource for the local economy.  The eastern oyster, Crassosstrea virginica, is an intertidal species that forms large banks along the edges of estuarine habitats.  One of these banks, known as Oyster Point, was particularly prominent.  Oyster Point is now known as downtown Charleston (Burrell 2003).  Not only did oysters provide the physical foundation for the city, they also were a major food source. Based on findings from archaeological excavations and historical documents, it is believed that all social classes ate oysters, as they were cheaper than most game species.  Mackey (1859) described the differences between classes saying, “the rich consume oysters with champagne and the poorer classes consume oysters and beer.” Unsurprisingly, oyster fisheries have been extremely important in the South Carolina economy for quite a while. In 1902, oyster fisheries made up over 42% of the total profit (Report of the Commissioner 1903). 

Because oysters are ubiquitous throughout Charleston history, historians and scientists are able to use their presence to roughly describe economic and ecological affairs of a particular time period.  Archeological digs allow one to delve into spatial and temporal variability of oysters within the Charleston region.  For example, some regions were made up of mostly wealthy residents, who would generally prefer the biggest and best oysters.  Smaller oysters found in this region could indicate an environmental disturbance that might have reduced the size of the oyster cohort for that time period.  Such evidence can be linked with other historical evidence to provide a more accurate idea of environmental and economic conditions of Charleston.

While archeological studies can provide novel and intriguing insights into historical economics and ecology, it is important to remember the inherent biases associated with this approach. Biases such as oyster selection by the harvesters, the buyers, and the archeological surveyors, would all likely select for larger oysters.  Therefore, the oyster data presented here may not represent the entire natural population, but may be more skewed towards harvesting preferences. The 3D printing methodology employed here provides a novel approach to recreating historical samples. However, this methodology recreated oysters based on samples that may have been degraded or broken over time.

Methods 

Oyster Collections/Processing

             Oyster samples were excavated/collected by the Charleston Museum from a total of five locations across Charleston, South Carolina-48 Laurens Street, the Aiken-Rhett House, the Beef Market, 86 Church Street, and the Stono Plantation near the Stono River (Figure 1). Oysters excavated from the Beef Market were determined to be from the years 1739-1796 and oysters from the Stono Plantation ranged in age from the 1700s and1800s to about 2000 years ago. Years were determined by the Charleston Museum based on pottery dating (Zierden and Reitz, 2005; Anthony, 2012). Live modern day oysters were collected from Dill’s Sanctuary near the Stono River in 2013. Modern day oysters were shucked and their tissues removed. Shells were bleached for 2 days, rinsed, and dried prior to labeling and measuring (Figure 2). All museum samples were labeled with an identification number correlating to the Museum information.

Figure 2. 48 Laurens House. Collections of The Charleston Museum.

Figure 3. 48 Laurens dig. Collections of The Charleston Museum.

Figure 4. Aiken-Rhett House. Collections of The Charleston Museum.

Figure 5. Aiken-Rhett dig. Collections of The Charleston Museum.

Figure 6. Church St. dig showing layers. Collections of The Charleston Museum.

Table 1. Historical period of oyster samples.

Measurements

             For each oyster sample a total of four measurements were taken for each the right and left handed valves-valve height, anterior scar height, valve length, and valve depth. Morphometric measurements were based on Claaseen (1998).

Figure 7. Oyster shell measurements analyzed.

Analyses

            Comparisons of morphometric measurements were made across locations and years using one-way ANOVAs and Tukey’s post-hoc tests. All analyses were performed using R Studio.

Results

            Results from morphometric data on the left valves of oysters collected from five distinct locations in Charleston, SC are displayed in the figures below. In general, oysters collected from the Beef Market were wider (increased valve length) (Figure 8) and deeper (increased shell depth) (Figure 9). There were no clear trends in differences in any of the metrics across the four different Stono River time periods. Additionally, there were no differences in anterior scar height between any of the different locations (Figure 11). 

Figure 8. Left valve length (mm) of oysters collected from 48 Laurens (n = 12), Aiken-Rhett (n =24), beef market (n = 13), Church Street (n = 30), Stono 0 AD (n = 37), Stono 1700 (n = 10), Stono 1800 (n = 177), and Stono 2013 (n = 129) Letters represent significant differences among locations based on post-hoc Tukey’s analysis.

Figure 9. Left shell depth (mm) of oysters collected from 48 Laurens (n = 10), Aiken-Rhett (n =24), beef market (n = 13), Church Street (n = 29), Stono 0 AD (n = 39), Stono 1700 (n = 9), Stono 1800 (n = 151), and Stono 2013 (n = 73) Letters represent significant differences among locations based on post-hoc Tukey’s analysis. 

Figure 10. Left valve height (mm) of oysters collected from 48 Laurens (n = 8), Aiken-Rhett (n =23), beef market (n = 13), Church Street (n = 27), Stono 0 AD (n = 39), Stono 1700 (n = 10), Stono 1800 (n = 182), and Stono 2013 (n = 128) Letters represent significant differences among locations based on post-hoc Tukey’s analysis. 

Figure 11. Left anterior scar height (mm) of oysters collected from 48 Laurens (n = 11), Aiken-Rhett (n =21), beef market (n = 13), Church Street (n = 29), Stono 0 AD (n = 35), Stono 1700 (n = 5), Stono 1800 (n = 163), and Stono 2013 (n = 130) Letters represent significant differences among locations based on post-hoc Tukey’s analysis. 

3D-Printed Historical Oyster Shells

In order to visualize the size differences among historical and modern oysters, 3D models of oyster shells were created using the average measurements of collected historical and modern oyster shells. A 3D scan of a modern oyster shell was obtained from Sketchfab (Creative Commons Attribution 4.0 International Public License) and used to create the 3D models. The original 3D scan created by the user tella and available on Sketchfab can be accessed here.

Figure 12. Example 3D oyster shell file.

Tinkercad was used to manipulate the original file to fit the dimensions of the various historical oyster shells. Average measurements for anterior scar height, valve length, valve height, and shell depth were used to re-create left oyster shells obtained from each time point and each collection site. Collection sites and time periods are listed in Table 1. 3D printing files can be accessed at the bottom of this page.

Figure 13. Example oyster shell in Tinkercad software.

Figure 14. Final product of 3D-printed oysters.

Discussion

            In 2013, the historical ecology of oysters project compared the sizes and shapes of naturally growing oysters that lived in the Stono River between 2000 ya and present day. They found that compared to ancient oysters, modern oyster are long, thin, and fairly shallow. In 2016, we have added samples from several historical sites in downtown Charleston to the dataset. These data sets, despite containing almost identical parameters, shed light on two very different topics.

            The 2013 dataset speaks to the power of adaptation to change population norms over time. It shows us empirically that oysters have changed in an observable way over the last two millennia, and it allows us to hypothesize about what may have caused these changes (e.g., pollution, consumption by early Charlestonians, etc). On the other hand, our newest additions to the historical oyster dataset come entirely from homes and commercial enterprises. They are in no way a record of natural populations, but are instead a catalogue of which oysters were being bought and sold, and by whom. This information has the potential to be very interesting from an anthropological standpoint.

            For example, extremely large oysters were found at the Beef Market site. This market was once one of the more popular venues to purchase goods in Charleston. On average, oysters collected from the Beef Market were larger than the average naturally occurring oysters of the time. Were these larger oysters present at the market because they were worth more than their smaller counterparts? Or were these larger oysters left on the floor of the market for some other reason? This mystery has the potential to paint an interesting picture concerning Charleston’s history and the oyster trade as it once stood.

            The new downtown dataset is far from complete. Only three residences have been excavated for oyster remains (i.e., Church Street, 48 Laurens Street, and the Aiken-Rhett house), but as this dataset continues to grow it could begin to elucidate many unknowns about historic Charleston. Is there a link between household income and the size of oyster shells found on the property? Did homes with servants consume more oysters than those without? Were oysters a more common treat along the waterfront than further inland? Though not strictly ecological in nature, these questions may prove to be important when considering current oyster populations and their conservation for future generations.

            These data act as a baseline. With so few sample sites, there are few conclusions to be made concerning historical Charleston and its effect on natural oyster populations, but with continued effort and expansion of the current dataset, new trends are sure to come to light.

References

Burrell, VG 2003.  South Carolina Oyster Industry: a history.  Self-published. 

Mackey, Charles. 1859. Life and Liberty in America. Smith, Elder & Co. NY., N.Y.

Report of the Commissioner for 1903. U.S. Commission of fish and fisheries. U.S. Govt. Printing Office. 1905.