Response and recovery dynamics of seagrasses Thalassia testudinum and Syringodium filiforme and macroalgae in experimental motor vessel disturbances

Shallow seagrass beds worldwide are being negatively impacted by human activities. Damage by boats includes anchor scars, propeller scars, and hull groundings. In some Thalassia testudinum-dominated systems, vessel damage may persist for years or decades, and even small scars may leave seagrass habitat susceptible to severe erosion by wind and wave-driven currents and storms. Cost-effective techniques for restoration in these erosion-prone systems must include sedi- ment replacement and stabilization to best enhance seagrass recovery. We conducted 2 experiments to address the effects of excavation depth and sediment filling on seagrass and macroalgal recovery into small-scale disturbances such as propeller scars. Recovery in excavations ≥20 cm deep took 2 to 5 yr longer than recovery in shallower disturbances (10 cm). Seagrasses were able to grow in native limestone fill material (diameter 0.6 cm), although the compensatory response of Syringodium filiforme was dampened.