Oyster Reefs as Natural Breakwaters Mitigate Shoreline Loss and Facilitate Fisheries

Scyphers, S. B., et al., 2011. Plos One

Original research (primary data)
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Shorelines at the interface of marine, estuarine and terrestrial biomes are among the most degraded and threatened habitats in the coastal zone because of their sensitivity to sea level rise, storms and increased human utilization. Previous efforts to protect shorelines have largely involved constructing bulkheads and seawalls which can detrimentally affect nearshore habitats. Recently, efforts have shifted towards “living shoreline” approaches that include biogenic breakwater reefs. Our study experimentally tested the efficacy of breakwater reefs constructed of oyster shell for protecting eroding coastal shorelines and their effect on nearshore fish and shellfish communities. Along two different stretches of eroding shoreline, we created replicated pairs of subtidal breakwater reefs and established unaltered reference areas as controls. At both sites we measured shoreline and bathymetric change and quantified oyster recruitment, fish and mobile macro-invertebrate abundances. Breakwater reef treatments mitigated shoreline retreat by more than 40% at one site, but overall vegetation retreat and erosion rates were high across all treatments and at both sites. Oyster settlement and subsequent survival were observed at both sites, with mean adult densities reaching more than eighty oysters m 22 at one site. We found the corridor between intertidal marsh and oyster reef breakwaters supported higher abundances and different communities of fishes than control plots without oyster reef habitat. Among the fishes and mobile invertebrates that appeared to be strongly enhanced were several economically-important species. Blue crabs (Callinectes sapidus) were the most clearly enhanced (+297%) by the presence of breakwater reefs, while red drum (Sciaenops ocellatus) (+108%), spotted seatrout (Cynoscion nebulosus) (+88%) and flounder (Paralichthys sp.) (+79%) also benefited. Although the vertical relief of the breakwater reefs was reduced over the course of our study and this compromised the shoreline protection capacity, the observed habitat value demonstrates ecological justification for future, more robust shoreline protection projects.

Case studies

Basic information

  • Case ID: INT-109-1
  • Intervention type: Restoration
  • Intervention description:

    constructing subtidal breakwater oyster reefs: Each reef complex was comprised of three 5 m625 m rectangular-trapezoid sections (Figure 3B). Each section consisted of loose oyster shell, purchased from a local seafood processing plant, placed on a geo-textile fabric to prevent subsidence and secured by a plastic mesh covering (with 1 cm2 openings) that was anchored by rebar...The subtidal design of the reefs allowed for maximum exposure for oyster settlement and increased available substrate for foraging by transient and larger resident fishes, while maximizing potential capacity for wave attenuation.

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Coastal erosion  Positive Vegetation shoreline retreat: permanent rebar stakes were installed at 25 m intervals along the 100 m stretch of shoreline at each replicate treatment. During each survey, marsh retreat was measured as the distance from the rebar stake to the living vegetation line. changes in nearshore depth profiles
  • Approach implemented in the field: Yes
  • Specific location:

    Mobile Bay and Mississippi Sound, Alabama (Gulf of Mexico) Site 1 - Point aux Pins (site center point: 30.370098,288.308578) Site 2 - Alabama Port (site center point: 30.347917,288.121338), is located along the southwestern shore of Mobile Bay, just north of the Dauphin Island bridge

  • Country: United States of America
  • Habitat/Biome type: Deltas and estuaries |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: Effectiveness determined by comparing to non-restored control sites For vegetation retreat measure: no effect of intervention at one site but marginally significant effect at other site (At Alabama Port, breakwater reefs mitigated vegetation retreat by more than 40% over two years). For changes in nearshore depth profiles (Port aux Pins site only): in addition to a general trend of decreasing depth, areas inshore of breakwater reefs appeared to gain more sediments than areas inshore of control plots
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: Yes
  • Impacts for the ecosystem: Positive
  • Ecosystem measures: restoration of oyster reefs - oyster recruitment rate and adult densities Fish and mobile invertebrate community composition, abundance, and species diversity Abundances of economically valuable species [Blue crabs (Callinectes sapidus) were the most clearly enhanced (+297%) by the presence of breakwater reefs, while red drum (Sciaenops ocellatus) (+108%), spotted seatrout (Cynoscion nebulosus) (+88%) and flounder (Paralichthys sp.) (+79%) also benefited.]
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures: n/a
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic: