Research ArticleENVIRONMENTAL STUDIES

Coral reef structural complexity provides important coastal protection from waves under rising sea levels

See allHide authors and affiliations

Science Advances  28 Feb 2018:
Vol. 4, no. 2, eaao4350
DOI: 10.1126/sciadv.aao4350
  • Fig. 1 Conceptual diagram showing the future scenarios of coral reef structural complexity and vertical reef accretion.

    The RHI measures the capacity of a coral reef to accrete vertically and maintain structurally complex coral communities, with red indicating a low RHI and blue indicating a high RHI.

  • Fig. 2 Changes in back-reef wave height for three scenarios.

    P1, coral reef degradation at present sea level; P2, the worst-case scenario by 2100; and P3, the most likely scenario by 2100. The circle markers show the mean result for each scenario. The mean of the present wave conditions (scenario S1 in the Supplementary Materials) is also shown as the cyan marker. The wave dissipation [in terms of H(-)] provided by coral reef structural complexity (fw) is shown by the orange arrowed line (present sea level) and black arrowed line (higher sea levels). The vertical dashed line represents present wave conditions where H(-) = 1, and the horizontal dashed line is the 50% probability line (P = 0.5).

  • Fig. 3 Box plots and distribution of Hrms2 for the three scenarios.

    P1, coral reef degradation at present sea level; P2, the worst-case scenario by 2100; P3, the most likely scenario by 2100; and S1, the coral reef under present conditions. Boxes show the interquartile range (IQR, 25th and 75th percentiles) of the Hrms2 values. Whiskers represent the distance of 1.5 IQR from the 25th and 75th percentiles, and circle markers show the median values. Dashed lines show the mean Hrms2 values of which correspond with the peak of the wave height distributions shown as solid lines. Wave height distributions were calculated probability density functions in MATLAB.

  • Fig. 4 Controls on future back-reef wave heights in coral reefs for scenario P3.

    The influence of sea-level rise (SLR), RR, structural complexity (fw), and RHI on wave height is shown for 40,000 model runs. (A) Scatterplot showing the influence of sea-level rise on normalized back-reef wave height (Hn, subscript n indicating normalized values between 0 and 1), with marker colors indicating the normalized values of structural complexity (fwn) for the model run, with blue indicating high fwn and red indicating low fwn. The dashed trend line is the linear regression result where Hn = 0.81SLR − 0.06 (R2 = 0.09). (B) Strong relationship between RHI and back-reef wave height with the dashed black line showing the fitted curve Hn = −0.66RHIn + 0.66 (R2 = 0.53). The dashed red line is the 1:−1 ratio shown for comparison. (C) Distribution of Hn due to changes in fw and RR.

  • Table 1 Calibrated free parameters Embedded Image in the wave dissipation model for each reef type (low to high energy).

    The mean wave friction factor (Embedded Image) and breaker criterion inputs for XBeach are shown. The root mean square error (RMSE) and the R2 correlation derived from linear regression between the modeled and measured reef flat and back-reef wave heights are also shown.

    Coral reef (energy)Embedded ImageγbR2RMSE
    Tiahura (low)0.30.90.980.006
    Temae (intermediate)0.2410.880.02
    Ha’apiti (high)0.110.90.940.02
    Teahupo’o (high)0.0310.920.028

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaao4350/DC1

    Description of model scenarios and results

    Model inputs

    Wave data collection

    Model calibration

    Offshore wave climate

    fig. S1. Schematic representation of the inputs into the wave dissipation simulations for the six scenarios (P1 to P3 and S1 to S3) described in the main text.

    fig. S2. Changes in back-reef wave height for different scenarios and energy regimes.

    fig. S3. Locations of the cross-reef bathymetric profiles and of the wave measurements for the four reef sites in Moorea and Tahiti.

    fig. S4. Global map of sea-level rise predictions by 2100 by the IPCC for the RCP4.5 and RCP8.5 scenarios.

    fig. S5. Example of time-averaged and individual wave heights for Tiahura near breakpoint.

    fig. S6. Comparison of the modeled and measured wave for each deployment location on the reef flats and lagoon of the four sites in Moorea and Tahiti.

    fig. S7. Example time series for Ha’apiti, Moorea.

    fig. S8. Summary of long-term offshore wave data (1979–2013) for Tahiti and Moorea from National Oceanic and Atmospheric Administration WAVEWATCH III (http://polar.ncep.noaa.gov/waves/index2.shtml) (150.05°W, 17.94°S).

    fig. S9. Comparison of the measrured offshore significant wave height (Hso) used to calibrate the XBeach wave model (study period) and the long-term averages from CRIOBE and Moorea LTER (4) measurements (long-term) for each reef site.

    table S1. Sources of bathymetric data sets for Moorea and Tahiti.

    References (58, 59)

  • Supplementary Materials

    This PDF file includes:

    • Description of model scenarios and results
    • Model inputs
    • Wave data collection
    • Model calibration
    • Offshore wave climate
    • fig. S1. Schematic representation of the inputs into the wave dissipation simulations for the six scenarios (P1 to P3 and S1 to S3) described in the main text.
    • fig. S2. Changes in back-reef wave height for different scenarios and energy regimes.
    • fig. S3. Locations of the cross-reef bathymetric profiles and of the wave measurements for the four reef sites in Moorea and Tahiti.
    • fig. S4. Global map of sea-level rise predictions by 2100 by the IPCC for the RCP4.5 and RCP8.5 scenarios.
    • fig. S5. Example of time-averaged and individual wave heights for Tiahura near breakpoint.
    • fig. S6. Comparison of the modeled and measured wave for each deployment location on the reef flats and lagoon of the four sites in Moorea and Tahiti.
    • fig. S7. Example time series for Ha’apiti, Moorea.
    • fig. S8. Summary of long-term offshore wave data (1979–2013) for Tahiti and Moorea from National Oceanic and Atmospheric Administration WAVEWATCH III (http://polar.ncep.noaa.gov/waves/index2.shtml) (150.05°W, 17.94°S).
    • fig. S9. Comparison of the measrured offshore significant wave height (Hso) used to calibrate the XBeach wave model (study period) and the long-term averages
      from CRIOBE and Moorea LTER (4) measurements (long-term) for each reef site.
    • table S1. Sources of bathymetric data sets for Moorea and Tahiti.
    • References (58, 59)

    Download PDF

    Files in this Data Supplement:

Navigate This Article