Seagrass extent, growth, and decline are mainly driven by the hydrodynamics affecting the physical environment for growth, the underwater light climate, and the availability of  nutrients. Seagrass stands have a feedback effect on the hydrodynamics, by increasing drag changing flow patterns, which impacts sediment transport and accumulation rates. Furthermore seagrass can reduce sediment resuspension by wind driven waves, with the associated reduction in turbidity enhancing seagrass growth. This study investigated the influence of sediment inputs on seagrass extent and condition, and the feedback mechanisms of seagrass on sediment transport within Western Port.

A simulation tool was developed combining a hydrodynamic transport and biogeochemical model (ELCOM-CAEDYM), a wave model (SWAN), and a seagrass growth model. The hydrodynamic model is driven by local meteorology and sea level variations, as well as river inflows and sediment loads derived from parallel development of catchment to coast hydraulic transport models. The wave model was implemented to infer resuspension of bottom sediments. Finally, a growth model for seagrass including shading effects through sedimentation as well as nutrient cycling was implemented into ELCOM-CAEDYM. The feedback mechanism of seagrass beds on flow and wave action itself was included using modified bottom roughness coefficients derived from field measurements . Simulation results of the combined model tools and a stand-alone growth model for seagrass are presented and their results compared to observed interannual variations of seagrass in Western Port.