Background

Historical Ecology in Charleston and Baselines

While ecology is the study of interactions between organisms and their environments, historical ecology examines the effects of these interactions over time and space. Through historical ecology, scientists can gain insight into how ecosystems have changed and the impact of humans on the natural world. One important aspect of historical ecology is determining a ‘baseline’ or point in time where the ecosystem was pristine and unaffected by man. However, given the lack of knowledge about some primitive cultures it can be difficult to ascertain when people first inhabited an area, how they lived, and thus their impact on the local ecosystem.

Archaeological evidence has suggested that native societies were in the Dill Sanctuary approximately 8,000 years ago (early Archaic period) and it is thought that these populations were feeding on a variety of native organisms including mollusks (Anthony 2012). Shell rings started appearing approximately 4,500-3,000 B.P., suggesting a potential shift to a bivalve dominated ecosystem in coastal S.C. as well as Georgia and Florida (Dame 2009). However, whether the ecosystem itself changed or whether this time period just marked an increase in harvesting of oysters by natives is not clear. Shell rings were built on salt marshes and ranged in size from 3-10 m tall and 20-250 m in diameter. The purpose of shell rings is not positively known, but some possible explanations include cultural monuments or fortifications (Saunders 2002). Construction of shell rings stopped around 3,000 B.P. which may have reflected a change in Native American lifestyle related to a change in the local ecosystem (Dame 2009).

When Europeans arrived to Charleston, S.C. in the late 17th century they also subsisted off local organisms. Maps from the 18th century identify downtown Charleston as “Oyster Point,” potentially signifying that there was a high abundance of oysters present in Charleston Harbor (which is not the case today). Therefore, it is hard to determine a true baseline for oyster populations in Charleston, S.C. because there is little information on the ecosystem prior to mass harvesting of oysters in the Archaic period. 

Ecological Importance of Oysters in Charleston

Oysters provide a plethora of valuable services to Charleston’s estuarine ecosystem.  Oyster reefs are essential habitat to many other organisms, including crabs, polychaete worms, gastropod molluscs, sponges, shrimp, nudibranchs.  In fact, they are considered “ecosystem engineers” because they modify portions of the harbor and facilitate the habitation of other species.  Oyster reefs provide substrate for settling organisms, like barnacles, anemones, sponges, and seaweeds.  They also greatly increase the complexity of mudflat habitats and provide shelter for a handful of small critters, including amphipods, isopods, crabs, shrimp, brittle stars, and worms.  Mudflats that have been transformed into oyster reefs experience a substantial increase in biodiversity and species abundance.

This cluster of so many species also provides many novel links in estuarine food webs and can interact with neighboring communities.  Shore birds and other predators can take advantage of these areas to forage for prey, and transfer energy to other distant estuarine or terrestrial communities.  The oysters themselves provide a delicious meal for a number of organisms, including oyster toadfish, oyster drills, Cliona sponges, and a number of crab species, which in turn act as prey for larger marine predators.  

In addition to having enormous biological impacts, oysters are also capable of altering the physical environment that surrounds them.  Sub-tidal oysters filter particulates out of seawater for feeding, and this happens at such a fast rate that they are actually capable of improving water clarity.  Decreasing water turbidity allows for an increase in the depth of the photic zone, which in turn increases primary productivity.  Particulate matter is not all they remove from the water column, however.  Oysters have moderately high uptake rates of ubiquitous environmental toxins, and act as a “sink” for compounds like PAHs, PCBs, and heavy metals, which are all contaminants of concern for human health but do not negatively affect oyster health.  By “cleaning” the water in this way, they directly reduce the risk of human exposure to these toxic substances (just don’t eat too many!).    

Past and Present Oyster Distribution in the Stono River 

Stono River in 1891 (oyster beds in red) (Battle, 1891)

Stono River in 2010 (oyster beds in yellow) (Map produced by Katie Luciano, SCDNR)