COS 7-7
Landscape context effects the ecosystem-service delivery of temperate biogenic reefs
Estuarine mudflats, seagrass meadows, saltmarshes, mangroves, and oyster reefs are valued for numerous ecosystem services such as fishery production, nutrient cycling (water filtration) and shoreline stabilization. Properly scaling these diverse services requires an understanding of how gradients in salinity, depth, habitat patch size or fragmentation, and inter-habitat connectivity (collectively: landscape) control the ecology and function of these coastal habitats. Our research has utilized a suite of natural and restored oyster reefs to explore how landscape context regulates service delivery. Here, we focus on the >100 subtidal and intertidal oyster reefs our group has restored throughout North Carolina to evaluate how landscape setting affects reef development and function. In particular, we have sampled reefs built either isolated from saltmarsh habitat, or immediately adjacent to saltmarsh. Since construction (ranging from 1997–2011 among reefs), we have repeatedly sampled these reefs to quantify oyster density/biomass, as well as associated nekton densities. Additionally, cores have been collected from reefs and processed in the lab to determine rates of nitrogen cycling (incubations) and carbon burial (core dissections). We have also used high-resolution (cm-scale) mapping approaches to quantify how reefs have impacted local sediment retention/accumulation over year-to-decade scales.
Results/Conclusions
We show that landscape context (i.e., connectivity with saltmarsh habitat and depth) is a key determinant of the type and magnitude of services that reefs provide. For instance, reefs isolated from marsh habitat and located intertidally tend to support high oyster densities and do buffer wave energy, but do not support mobile fauna nor contribute much towards carbon burial. Based primarily on the tight linkages between oyster density and nitrogen cycling, these reefs also promote higher rates of denitrification. Conversely, patch reefs directly connected to saltmarshes, or located in the shallow subtidal, do not typically become consolidated reefs with high oyster densities, but can function as essential fish habitat (moreso than reefs in alternative landscape contexts). In low-medium energy environments, saltmarsh-fringing reefs can also promote marsh stabilization/expansion and aid in carbon burial. Efforts to capture the overall value of oyster habitat relative to ecosystem-service delivery must account for these alternative outcomes when designing local and regional plans to promote shellfish reef conservation and restoration.