Shoreline Hardening Affects Nekton Biomass, Size Structure, and Taxonomic Diversity in Nearshore Waters, with Responses Mediated by Functional Species Groups

Coastal shoreline hardeningis intensifying due to human population growth and sea level rise. Prior studies have emphasized shoreline- hardeningeffects on faunal abundance and diversity; few have examined effects on faunal biomass and size structure or described effects specific to different functional groups. We evaluated the biomass and size structure of mobile fish and crustaceanassemblages within two nearshorezones (waters extending 3 and 16 m from shore) adjacent to natural (native wetland; beach) and hardened(bulkhead; riprap) shorelines. Within 3 m from shore, the total fish/ crustaceanbiomass was greatest at hardenedshorelines, driven by greater water depth that facilitated access to planktivore(e.g., bay anchovy) and benthivore- piscivore(e.g., white perch) species. Small-bodied littoral-demersal species (e.g., Fundulusspp.) had greatest biomass at wetlands. By contrast, total biomass was comparable among shoreline types within 16 m from shore, suggesting the effect of shoreline hardeningon fish biomass is largely within extreme nearshoreareas immediately at the land/water interface. Shoreline type utilization was mediated by body size across all functional groups: small individuals (≤60 mm) were most abundant at wetlands and beaches, while large individuals (>100 mm) were most abundant at hardenedshorelines. Taxonomic diversity analysis indicated natural shoreline types had more diverse assemblages, especially within 3 m from shore, although relationships with shoreline type were weak and sensitive to the inclusion/exclusion of crustaceans. Our study illustrates how shoreline hardeningeffects on fish/ crustaceanassemblages are mediated by functional group, body size, and distance from shore, with important applications for management.