Effects Of Shoreline Development And Oyster Reefs On Benthic Communities In Lynnhaven, Virginia

Field: Environmental Science (Physical Sciences)

Shoreline hardening and construction of restoration oyster reefs are occurring at rapid rates throughout Chesapeake Bay and little research has been conducted to determine whether installment of a hardened shoreline and oyster reef placement has an effect on the surrounding benthic infaunal communities. I investigated the effects of shoreline development and oyster reefs on benthic communities in Lynnhaven, Virginia. Throughout Lynnhaven, I determined the effects of shoreline type (natural marsh, oyster reef, rip-rap and bulkhead), sediment grain size, Total Organic Carbon/Total Nitrogen (TOC/TN) of the sediment, and predation (caging study) on density, biomass, and diversity of benthic infauna. An information-theoretic approach using Akaike’s Information Criterion (AIC) was used. Of the variables measured, shoreline type was the best predictor of benthic infaunal density (highest density at oyster reefs and lowest at bulkheads), while sediment composition (grain size and TOC/TN) and predators were the best predictors of biomass and diversity. Lynnhaven is a polyhaline, shallow, semienclosed, natural marsh-dominated system with high overall productivity, which could be masking any small-scale disturbances due to shoreline hardening at the sites. A Before-After-Control-Impact (BACI) study was completed at two sites (Eastern Branch and Linkhorn Bay) in Lynnhaven to examine the benthos before and after placement of oyster reefs. Replicate samples for benthic infauna, sediment grain size, and sediment TOC/TN were taken before and one year after reef placement. Based on the AIC analysis, oyster reefs had a positive effect on infaunal density at the Linkhorn Bay site after one year, mainly attributed to an influx of the bivalve Gemma gemma. The density increase occurred even with a decrease in polychaete density. There was no change in infaunal biomass or diversity at this site. At the Eastern Branch site, there was no effect of oyster reefs on density, biomass, or diversity. To characterize the benthos prior to reef placement, benthic samples were collected at two sites (Eastern Branch and Linkhorn Bay) in Lynnhaven. Four reef types (oyster shell, rip-rap, concrete modules, and reef ball) were deployed at both sites. Oyster production values for existing oyster reefs were used to estimate expected oyster production on each reef type. Biomass estimates and published P:B ratios for each taxa were used to calculate secondary production for benthic infauna and oysters. Lost benthic production due to each reef type at both sites was compared to estimated oyster production on each reef type to determine if each reef compensated for benthic production lost by placing the reefs on top of the benthos. Oyster production on oyster shell and reef ball reefs compensated for benthic production lost due to placement of the reefs at both sites. Oyster productivity on rip-rap and concrete module reefs did not compensate for lost benthic production at the highly productive Eastern Branch site, and barely compensated for lost benthos at the lower productivity Linkhorn Bay site. The preservation of natural marsh and use of the proper types of oyster reefs could help maintain the high productivity of both the benthic community and the Lynnhaven system itself.