Do oyster breakwater reefs facilitate benthic and fish fauna in a dynamic subtropical environment?
Chowdhury, Mohammed Shah Nawaz ; Shahadat Hossain, M. ; Ysebaert, Tom ; Smaal, Aad C. - \ 2020
Ecological Engineering 142 (2020). - ISSN 0925-8574
Oyster breakwater reefs used for coastal protection have shown to enhance local biodiversity. Particularly, macro-invertebrate and fish assemblages can benefit directly from reefs providing structurally complex habitats and indirectly through alteration of soft-sediment environment near the reef areas. To test this hypothesis, a manipulative field experiment was carried out on an eroding intertidal flat in the southeastern coast of Bangladesh by deploying replicate units of each 20 m long oyster breakwater reefs specially designed to protect adjacent shorelines. Transient fishes and resident intertidal macro-invertebrate communities were assessed monthly for a period of 18 months. On the intertidal flat, five transects were setup for faunal and environmental data collection, three crossing the breakwater reefs and two along the control areas without reefs. Prior to the deployment of the reefs, both the macro-invertebrate and fish assemblage were not significantly different among the five transects, indicating a rather uniform distribution of species in all tidal flats. Data collected post-reef deployment revealed that oyster breakwater reefs supported a greater biomass as well as abundance of benthic macro-invertebrates on the landward mudflat behind the reefs than the mudflat of control sites. The community structure, and seasonal variation of the macrobenthic community were associated with the variations in the sediment accumulation, as influenced by the breakwater reefs. Additionally, higher abundance of transient finfish and mobile macro-invertebrates at the reef sites suggest that the faunal communities were attracted by the higher abundance of prey resources (i.e. polychaetes, small crustaceans, juvenile gastropods and bivalves) as supported by the reefs. Thus, the reef areas served as shelter, nursery, and foraging grounds for different species. Though the ecological benefits of using oyster breakwater reefs only span adjacent to the reefs, this study confirms the importance of reef structure in facilitating local coastal biodiversity in a subtropical region.
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.