Structure and Function of Restored and Natural Salt Marshes: Implications for Ecosystem Resilience and Adaptive Potential

Abstract

Salt marshes have ecological and economic value, but shoreline development, the increasing rate of sea-level rise, and other human impacts have caused significant loss of salt marshes. As a result, restoration of these ecosystems is widespread. For restoration and management to be effective, it is imperative to improve our understanding of marsh-building plants that serve as the ecological foundation of these habitats. Given the observed differences in characteristics between populations of smooth cordgrass, Spartina alterniflora, restoration plantings may impact the biodiversity and resilience of restored ecosystems. Understanding differences in the structural and functional outcomes of active planting of restoration sites will enable the long-term success of restoration efforts to be improved. Natural and restored salt marshes in Long Island Sound were studied in 2021–2022 for S. alterniflora genetics, biomass, stem morphology, and faunal community composition. The average genotypic diversity of S. alterniflora was more than 4 times higher in restored than in natural marshes, and differentiation between each restored site and natural sites decreased with time. No difference was observed in live S. alterniflora belowground biomass; however, mean dead belowground biomass in natural marshes was more than 3 times greater than in restored marshes. Marsh platform invertebrates differed between the restored and natural sites, with natural marsh edge habitats having 9 times higher density of Geukensia demissa and 3 times as many crab burrows than in restored marshes, but there was no detected difference in species richness or abundance of nekton at high tide. With restoration practitioners seeking resilient, self-sustaining ecosystems, it is important to evaluate whether restored marsh characteristics are consistent with those goals and modify restoration planning accordingly to incorporate genetics, structure, and function.