Functional dynamics of vegetated model patches: The minimum patch size effect for canopy restoration

Highlights: • A minimum seagrass patch size is needed for successful canopy restoration • The response of seagrass patches depends on wave velocity and canopy density. • Under low velocities seagrasses do not interact with waves, but attenuate seabed TKE. • Under moderate to high wave velocities seagrasses interact with waves producing TKE. For the past two centuries coastal zones have been suffering seagrass loss resulting in a network of vegetated patches which are barely interconnected and which may compromise the ecological services provided by the canopy. To optimize management efforts for successful restoration strategies, questions need to be addressed about what appropriate canopy architectural considerations are required under certain hydrodynamic conditions. In this study, a set of laboratory experiments were conducted in which hydrodynamic conditions, plant densities and vegetated patch lengths were varied to determine minimum patch lengths for successful management strategies. Based on the TKE production, this study finds two possible canopy behaviours of seagrasses under oscillating flows: one where plants do not interact with the flow and the other where they interact with waves and produce TKE. A threshold from the first to second behaviour occurs for ${\left(C_{D-\mathrm{Patch}}\frac{n{d}^2}{2\left(1-\varphi \right)}\right)}^{\frac{1}{3}}{U}_w$ = 2, where C_D is the drag of the vegetated patch, n is the number of stems per m², d is the stem diameter and ϕ is the solid plant fraction. Therefore, high canopy densities, large patches of vegetation or moderate wave velocities will produce plant-wave interaction, whereas low canopy densities, small vegetation patches or slow wave velocities will produce a behaviour akin to the non-vegetated cases.