Affiliation: College of Arts and Sciences, Department of Marine Sciences
Bulkheads represent a hardened shoreline stabilization structure designed to inhibit shoreline erosion and damage to coastal property. As sea level continues to rise, natural marshes can be sustained by transgression landward. The presence of a bulkhead, rip-rap revetment, or hybrid of those two, however, prevents transgression by fixing the location of the upper marsh. Simultaneously, as sea levels rise, wind-driven waves from storms and boat wakes erode the lower edge of the marsh, inducing slumping of the marsh platform into the sound. So marsh width, and thereby area, is declining in the squeeze between the fixed bulkhead and the rising waters, ultimately leading to its disappearance. We quantify and compare use by nekton (fish and crustaceans) and birds of marshes in front of bulkheads but differing in width from bulkhead to shoreline edge, and use width as an inverse proxy for time since marsh establishment to infer temporal habitat changes. Within three geographic areas of North Carolina, meteorologically driven Pamlico Sound in Kitty Hawk Bay, a strongly astronomically driven southern region along the Intracoastal Waterway around Wilmington, and a central region in Bogue Sound with mixed tidal forcing, we established five bulkheaded marsh sites with varying marsh widths of 0 to 40 m plus 1 non-bulkheaded marsh. Intensity of marsh use (abundance in fyke nets) for both fish and crustaceans exhibited similar responses of linear increase with marsh width over three geographic areas, two seasons, and two years. This repeated pattern implies that nekton use in marshes below shoreline stabilization structures declines over time as marsh width is reduced. Nekton density per unit marsh area sharply declined with increasing marsh width, implying that even the smallest marsh remnants have important habitat functions and deserve continued protection. Community compositions of birds using the shorelines varied significantly among the three regions, which differ dramatically in tidal excursion. We conclude that coastal marsh condition influences important aspects of bird use and marsh itself is critical to sustaining a diversity of bird guilds. The continued installation of bulkheads will promote marsh loss as sea level rises, ultimately degrading avian ecosystem services of coastal marshes.