Fish and Blue Crab Density along a Riprap-Sill-Hardened Shoreline: Comparisons with Spartina Marsh and Riprap

摘要

Wetland managers have historically considered riprap-sill structures (a type of "living shoreline" consisting of a rock sill that is placed low in the intertidal zone, with native vegetation planted between the sill and the shore) to be more ecologically sound than the riprap that is traditionally applied for shoreline stabilization in estuaries. However, little research has been conducted to compare the macrofauna associated with riprap-sill and riprap-hardened shorelines. Density and diversity of fish and blue crabs Callinectes sapidus were compared via weekly sampling along a riprap-sill shoreline, a riprap shoreline, and a shoreline fringed with smooth cordgrass Spartina alterniflora marsh in the Delaware Coastal Bays during summer 2010. Seining was conducted to quantitatively sample the shore zone and shallow subtidal regions, and minnow traps were used to determine the presence or absence of fishes in the mid-to upper-intertidal zone of each shoreline type. Temporally persistent differences in macrofaunal density and diversity were evident among the three shoreline types. In terms of fish density and diversity metrics, riprap-sill was more similar to the smooth cordgrass shoreline than to the traditional riprap shoreline. These results provide evidence for the biological advantage of riprap-sill over traditional riprap as a shoreline modification structure; spatial confirmation by further studies at different locations is warranted.