Evidence of exceptional oyster-reef resilience to fluctuations in sea level

Ridge, J. T., et al., 2017. Ecology and Evolution

Original research (primary data)
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Ecosystems at the land-sea interface are vulnerable to rising sea level. Intertidal habitats must maintain their surface elevations with respect to sea level to persist via vertical growth or landward retreat, but projected rates of sea-level rise may exceed the accretion rates of many biogenic habitats. While considerable attention is focused on climate change over centennial timescales, relative sea level also fluctuates dramatically (10-30cm) over month-to-year timescales due to interacting oceanic and atmospheric processes. To assess the response of oyster-reef (Crassostrea virginica) growth to interannual variations in mean sea level (MSL) and improve long-term forecasts of reef response to rising seas, we monitored the morphology of constructed and natural intertidal reefs over 5years using terrestrial lidar. Timing of reef scans created distinct periods of high and low relative water level for decade-old reefs (n=3) constructed in 1997 and 2000, young reefs (n=11) constructed in 2011 and one natural reef (approximately 100years old). Changes in surface elevation were related to MSL trends. Decade-old reefs achieved 2cm/year growth, which occurred along higher elevations when MSL increased. Young reefs experienced peak growth (6.7cm/year) at a lower elevation that coincided with a drop in MSL. The natural reef exhibited considerable loss during the low MSL of the first time step but grew substantially during higher MSL through the second time step, with growth peaking (4.3cm/year) at MSL, reoccupying the elevations previously lost. Oyster reefs appear to be in dynamic equilibrium with short-term (month-to-year) fluctuations in sea level, evidencing notable resilience to future changes to sea level that surpasses other coastal biogenic habitat types. These growth patterns support the presence of a previously defined optimal growth zone that shifts correspondingly with changes in MSL, which can help guide oyster-reef conservation and restoration.

Case studies

Basic information

  • Case ID: INT-100-1
  • Intervention type: Restoration
  • Intervention description:

    Constructed reefs began as mounds of loose, recycled oyster shell (cultch shell) measuring 3 × 5 × 0.15 m (width × length × height), followed by natural recruitment of oyster larvae from the estuary

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Coastal inundation  Positive mean vertical accretion (cm/yr), volume change (m3/yr), elevation shift of reef 'optimal growth zone' in response to changes in MSL
  • Approach implemented in the field: Yes
  • Specific location:

    C. virginica oyster reefs located in the Rachel Carson Research Reserve (North Carolina National Estuarine Research Reserve, NCNERR), Back Sound, North Carolina, USA (all reefs are within 2 km of 34.693007°N, 76.621709°W,

  • Country: United States of America
  • Habitat/Biome type: Deltas and estuaries |
  • Issue specific term: Green/blue infrastructure


  • Notes on intervention effectivness: effectiveness evaluated by monitoring change over time and comparing to a benchmark (MSL) evidence valid for ecological outcomes because indicate maintenance of the reef habitat which is stated to be of critical importance for natural coastal habitats/ecosystems
  • 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: same measures as climate impact effectiveness: mean vertical accretion rate, volume growth rate, shift in optimal growth zone to track changes in MSL
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • 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: No
  • Experimental evalution done: Not applicable
  • Non-experimental evalution done: Empirical case study
  • Study is systematic: