The Consequences of Shoreline Development for Near-Shore Communities in Chesapeake Bay, USA: A Before-After Control-Impact Study

• Main Author: Davenport, Theresa M.
• Format: Others
• Language: English
• Published: W&M ScholarWorks 2012
• Subjects: Environmental Sciences; Geography
• Online Access: https://scholarworks.wm.edu/etd/1539617914; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=3044&context=etd

Hardened shorelines and their construction introduce stressors to a system by altering near-shore habitats. They can reduce biodiversity and abundance of benthic infauna and marsh-edge nekton and epifauna. In this study, I investigated the impacts of shoreline development on near-shore communities using a temporal and spatial approach, by use of a before-after control-impact (BACI) study design at four sub-estuaries within Chesapeake Bay that represent three different types of shoreline change. The BACI study was used to examine infaunal density, biomass, and diversity for two size classes of infauna (3-mm: larger species and adults, 500-!m: smaller species and juveniles), as well as abundance of blue crabs and abundance and diversity of near-shore fishes before and after shorelines were modified. Data were analyzed with Akaike’s Information Criterion to compare candidate sets of linear models that contained year, shoreline treatment, sediment grain size, and salinity as predictors. In response to shoreline modification, infaunal density and biomass increased at sites that were newly developed (Timberneck, Dandy, and Holly Cove), but decreased at the site that changed from bulkhead to living shoreline (Windy Hill). In addition, infaunal diversity decreased at Timberneck and Windy Hill. Blue crab abundance increased at Timberneck, remained constant at Dandy, and decreased at Holly Cove. Blue crab abundance decreased at Windy Hill, though this may not be a shoreline modification response, as crabs concomitantly decreased at control shorelines. Fish abundance and diversity showed no distinct shoreline response at any site, which may reflect their transient nature. At Timberneck, infaunal responses to shoreline modification were mainly driven by changes in habitat. At Dandy, and Holly Cove, infaunal responses to shoreline modification were mainly driven by opportunistic species. At Windy Hill, infaunal responses were driven by a more uniform reduction in all species after the conversion. Sediment grain size was an important predictor of infaunal response variables at Timberneck and Holly Cove, and also changed concomitantly with shoreline modification at Timberneck. Salinity was an infrequent predictor of infaunal responses, though it did vary between years. The importance of opportunistic species and changes in sediment grain size one year after shoreline modification emphasizes the need to monitor shoreline modifications as ecological disturbances and changes in habitat, and the need to consider the role of shoreline modification in ecological succession rather than compare shorelines as static habitats. Lengths of shorelines that were modified were generally short, except at Windy Hill. Negative impacts of shoreline modification at Windy Hill likely reflect a larger disturbance than other sites, and a longer time needed to see positive improvements expected with a living shoreline. Fish species are more motile in nature, may be faster positive responders to positive changes in shoreline condition than infaunal benthos, and provided a first look at the positive effects of living shorelines at Windy Hill.