Intra-reef Surface Complexity of the Oyster Saccostrea glomerata and Its Influence on Surrounding Flow

Abstract Oyster reef restoration increasingly pursues the goal of enhancing coastal protection that can lead to a reduction in loading on shorelines through flow attenuation of waves and currents. However, flow attenuation is dependent on factors such as reef submergence, width and complexity. Yet the relationship between elements of the oyster reef landscape and flow attenuation is still not fully understood, making it challenging to design nature-based solutions for coastal protection. The topographical roughness characteristics of Sydney rock oyster ( Saccostrea glomerata ) reef surfaces were investigated using spatial statistics extracted from digital elevation models. Oyster agglomerations were classified into three distinct structural classes (Patch I, Patch II and Cluster) to differentiate intra-reef complexity. Patch I types had greater roughness heights (total roughness height, k t = 74 ± 10 mm) than Patch II ( k t = 56 ± 9 mm). Benthic flow instantaneous velocity readings were taken at windward, leeward and on-reef points for each delineated structural class. Of the samples examined, observations were made that oyster beds with higher k t values experienced greater flow reduction. While a direct link cannot be established, with future work, the results of this study can assist in achieving meaningful targets for patch-scale oyster reef restoration substrate.