Nekton assemblages along riprap-altered shorelines in Delaware Bay, USA: comparisons with adjacent beach

Riprap-reinforced shorelines are becoming more prevalent as a result of increasing coastal development and sea level rise. Altered morphology at the land-water interface, associated with riprap shorelines, has the potential to reduce shore-zone habitat quality for associated nekton species. The shore-zone nekton assemblage within a temperate, mid-Atlantic coast, USA, estuary was examined to identify differences in habitat use between sandy beach and riprap shorelines. We found that riprap can have a negative effect on a local scale. Overall nekton density, species richness, and density of dominant species were higher along beach shorelines relative to adjacent riprap, in most instances. Nekton association with shoreline habitat appears to be consistent over the diel cycle. Densities of Atlantic silverside Menidia menidia, striped killifish Fundulus majalis, spot Leiostomus xanthurus, and white perch Morone americana were generally reduced along riprap. In some cases, riprap shorelines also had altered species assemblages. Thus, our findings provide evidence of altered habitat quality for shore-zone nekton associated with shoreline hardening. These impacts were, however, variable spatially and temporally. Further research is needed to identify the biophysical mechanisms associated with riprap shorelines that are most responsible for altered habitat quality.