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

Denise L Breitburg,Matthew S Kornis,Steve Giordano,Lori A Davias,Donna M Bilkovic

doi:10.1007/s12237-017-0214-5

Abstract

Coastal shoreline hardening is intensifying due to human population growth and sea level rise. Prior studies have emphasized shoreline-hardening effects 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 crustacean assemblages within two nearshore zones (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/crustacean biomass was greatest at hardened shorelines, 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., Fundulus spp.) had greatest biomass at wetlands. By contrast, total biomass was comparable among shoreline types within 16 m from shore, suggesting the effect of shoreline hardening on fish biomass is largely within extreme nearshore areas 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 hardened shorelines. 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 hardening effects on fish/crustacean assemblages are mediated by functional group, body size, and distance from shore, with important applications for management.

Highlights

Estuaries and coasts are among the world’s most ecologically productive ecosystems, providing numerous ecosystem services benefitting society (Lotze et al 2006; Barbier et al 2011)
Demand for shoreline hardening is driven by desire to protect coastal land from erosion, and as such, shoreline hardening will likely increase with global sea level rise (Rahmstorf 2007; Arkema et al 2013) and increasing human populations in coastal areas (Crossett et al 2004)
Our results indicate that the response of estuarine fish and crustacean biomass and size structure to shoreline hardening varies substantially among functional groups, and by the width of the land/water ecotone considered

Summary

Introduction

Estuaries and coasts are among the world’s most ecologically productive ecosystems, providing numerous ecosystem services benefitting society (Lotze et al 2006; Barbier et al 2011). Estuaries and Coasts (2018) 41 (Suppl 1):S159–S179 et al 2008; Barbier et al 2011) Among these stressors, shoreline hardening has gained notoriety for numerous adverse ecological effects (e.g., Dugan et al 2011; Gittman et al 2016a). Replacement of natural shoreline by hardened structures (e.g., bulkheads, seawalls, riprap revetments) is growing in coastal areas (Brody et al 2008; Gittman et al 2015) where natural shorelines including tidal wetlands have already incurred substantial losses (Lotze et al 2006; Gedan et al 2009; Barbier et al 2011). Very few studies have examined how faunal biomass and size structure might be affected by shoreline hardening, such effects may be substantial and have important implications for coastal management

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