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.
Three oyster reefs were constructed on a tidal mud at of Kutubdia Island using precast concrete rings. these reefs were deployed parallel to the coastline (~0.5 m above mean lower low water, MLLW) as wave-break structures to attenuate wave energy. Prior to the deployment of the reefs, ECOBAS project used the concrete rings on the intertidal mud- at adjacent to the experimental site (at the same tidal exposure) for two years to allow oyster larvae settlement and grow50. During the rst year, settlement of oysters was low (<100 spat m−2). However, successful spat fall (>300 spat m−2) was observed in year two, when rings covered with high densities of oysters S. cucullata (~1200 individuals m−2; size class 5–47 mm shell length) and other marine organisms such as barnacles, sea anemones, gastropods and polychaetes. e overgrown rings were transported to the experimental site in March 2016 and termed as “oyster breakwater reefs”.
|Climate change impacts||Effect of Nbs on CCI||Effect measures|
|Coastal erosion||Positive||Adaptation/DRR: climate impacts is coastal erosion: wave attenuation / sedimentation and erosion rates / sediment deposition / resultant elevation profiles of mudflats, mangroves, sea grass / changes in tidal flat morphology / sediment grain size|
Kutubdia island (Fig. 7), located in the southeast coast of Bangladesh.