Oyster breakwater reefs promote adjacent mudflat stability and salt marsh growth in a monsoon dominated subtropical coast
Chowdhury, Mohammed Shah Nawaz ; Walles, Brenda ; Sharifuzzaman, Sm ; Shahadat Hossain, M. ; Ysebaert, Tom ; Smaal, Aad C. - \ 2019
Scientific Reports 9 (2019)1. - ISSN 2045-2322
Oyster reefs have the potential as eco-engineers to improve coastal protection. A field experiment was undertaken to assess the benefit of oyster breakwater reefs to mitigate shoreline erosion in a monsoon-dominated subtropical system. Three breakwater reefs with recruited oysters were deployed on an eroding intertidal mudflat at Kutubdia Island, the southeast Bangladesh coast. Data were collected on wave dissipation by the reef structures, changes in shoreline profile, erosion-accretion patterns, and lateral saltmarsh movement and related growth. This was done over four seasons, including the rainy monsoon period. The observed wave heights in the study area ranged 0.1–0.5 m. The reefs were able to dissipate wave energy and act as breakwaters for tidal water levels between 0.5–1.0 m. Waves were totally blocked by the vertical relief of the reefs at water levels <0.5 m. On the lee side of the reefs, there was accretion of 29 cm clayey sediments with erosion reduction of 54% as compared to control sites. The changes caused by the deployed reefs also facilitated seaward expansion of the salt marsh. This study showed that breakwater oyster reefs can reduce erosion, trap suspended sediment, and support seaward saltmarsh expansion demonstrating the potential as a nature-based solution for protecting the subtropical coastlines.
Growth potential of rock oyster (Sacosstrea cucullata) exposed to dynamic environmental conditions simulated by a Dynamic Energy Budget model
Chowdhury, Mohammed Shah Nawaz ; Wijsman, Johannes W.M. ; Shahadat Hossain, M. ; Ysebaert, Tom ; Smaal, Aad C. - \ 2019
Journal of Sea Research 147 (2019). - ISSN 1385-1101 - p. 19 - 27.
DEB model - Food - Monsoon - Saccostrea cucullata - Spatial and temporal variation
A Dynamic Energy Budget (DEB) model for the intertidal rock oyster (Saccostrea cucullata) is presented and applied for three different sites (Sonadia, Kutubdia and Inani) located in the south-eastern coast of Bangladesh, covering a distinct environmental gradient. At the three sites, field observations of oyster growth, temperature, total particulate matter (TPM) and food availability (Chlorophyll-a and Particulate Organic Matter-POM) were carried out during a period from September 2014 to August 2017. DEB model simulations produced temporal, as well as spatial variation in oyster growth as a function of the prevailing environmental conditions. Growth rates of oysters were highest (shell increment: 3 cm yr) at Sonadia Island due to the high food concentrations. Growth rates were relatively low (shell increment: 1.94 cm yr−1) at Kutubdia and none of oysters survived in Inani during the monsoon period. At this site TPM concentrations were quite high (889 ± 101 mg l−1), but Chlorophyll-a was quite low (1.86 ± 0.16 μg l −1) during monsoon period. Temporal variation is largely monsoon driven. The period between November to May was the main growing season for oysters along the Bangladesh coast. In contrast, growth slowed down significantly during the monsoon months (June–September). DEB model simulations for S. cucullata showed good fit (Goodness of fit score > 8.54 out of 10 and low mean relative error, MRE <0.18) with observed growth data for all three locations throughout the seasons. Therefore, the model can be used to evaluate potential sites for oyster development either for aquaculture, restoration or coastal protection to enhance coastal resilience.