Influence of Macrobenthos (Meretrix meretrix Linnaeus) on Erosion-Accretion Processes in Intertidal Flats: A Case Study From a Cultivation Zone

The activity of benthic organisms can strongly influence sediment dynamics in an intertidal flat. However, few studies have conducted a quantitative assessments of the effect of benthic organisms on erosion-accretion processes under field conditions. The aim of this study was to quantify the effects of the benthic clam Meretrix meretrix Linnaeus (M. meretrix) on bed erodibility and sediment erosion-accretion processes in an intertidal flat. Within the cultivation zone at site A, M. meretrix is present in large numbers (up to 137 individuals per square meter). On the other hand, site B is located outside the cultivation zone. At this site, which is only 500 m away from site A alongshore, M. meretrix forms a sparse population with only 3.7 individuals per square meter. The results showed that the critical shear stress for erosion, denoted by τ_ce, was 0.22 and 0.32 N/m² at sites A and B, respectively, and the magnitudes of bed-level change were significantly higher at site A than site B. These results reveal the large effect of M. meretrix on decreasing τ_ce, augmenting the erosion rate when the bed shear stress due to combined currents and waves, denoted by τ_cw, was higher than τ_ce, and conversely enhancing the accretion rate when τ_cw < τ_ce. The changes induced in these parameters are likely to have a large impact on model predictions of bed erodibility, sedimentary processes, and morphological evolution. Thus, integrated field measurements of hydrodynamic and bed-level changes, accompanied by simultaneous biological sampling, may help to improve the parameterization of hydro-sedimentary and morphodynamic models for shallow-water environments.