Comparison of the influence of patch-scale and meadow-scale characteristics on flow within seagrass meadows: a flume study

Hydrodynamic processes are an important agent of stress and facilitation in seagrass meadows, but little is known about the effects of the common phenomenon of heterogeneity of seagrass meadows on their interactions with hydrodynamic processes. To address this gap in knowledge, 4 heterogeneous configurations of Posidionia oceanica mimics were analyzed in a laboratory flume. The 4 configurations were created by placing 4 boards of mimics, i.e. 2 with high shoot density (similar to 1100 shoots m(-2)) and 2 with low shoot density (similar to 400 m(-2)), in different patterns (checkerboard, parallel, dense-sparse, and sparse-dense). Our results show that volumetric flow rate through each canopy, which is an indicator of the rate of supply of resources transported by the flow, tended to be greater in the low-density patches, regardless of the configuration. We also found that the Reynolds stress component tau(Re) was positive in the lower-density patches (indicating that horizontal momentum was being transferred into the patch) and negative in the high-density patches (indicating that horizontal momentum was being transferred upwards out of the patch). Our results suggest that in resource-limited environments, hydrodynamic processes favor the growth of lower-density patches in heterogeneous seagrass meadows, thereby causing meadows to become more homogeneous over time.