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

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-pm: 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. The consequences of shoreline development for near-shore communities in Chesapeake Bay, USA: a before-after control-impact study INTRODUCTION Ecosystem Function and Shoreline Development in Mid-Atlantic Estuaries Within the Mid-Atlantic United States, estuarine subtidal benthic fauna provide many ecosystem functions such as secondary production and trophic transfer (Valiela 1995, Seitz et al. 2003, 2005), benthic-pelagic coupling (Caliman et al. 2007), and cycling and storing toxicants (Diaz and Schaffner 1990). Infauna in Chesapeake Bay are responsible for production of about 194,000 metric tons C yr'1, supporting 27,500 mt of fisheries yield (Diaz and Schaffner 1990). Benthic infauna serve as critical links (benthic-pelagic couplers) between sources of organic matter in estuaries, consuming carbon from phytoplankton, benthic microalgae and macroalgae, and detritus, and providing food for economically and ecologically important finfish and crustaceans, such as the blue crab Callinectes sapidus (Seitz et al. 2001, 2003, Caliman et al 2007, Gillett and Schaffner 2009). About 50 % of fish production in Chesapeake Bay is linked to the benthic food web (Baird and Ulanowicz 1989), and benthic-feeding (demersal) nekton landings yielded an average of $39.8 million of revenue between 1998-2002 (Gillett and Schaffner 2009). Benthic communities affect water and sediment quality in estuaries. Filter feeding organisms in the benthos remove particles from the water column, leading to faster deposition than natural sinking can provide (Graf and Rosenberg 1997), resulting in enhanced water clarity and SAV coverage (Gillett and Schaffner 2009). Biodeposition by filter feeders may transfer water-column production to the sediment bed, where benthic, not pelagic, processes determine transport, transformation, and fates of sediments (Cohen et al. 1984). Bioturbation, or biological structuring and reworking of