Water flow in tide- and wave-dominated beds of the seagrass Thalassia testudinum

Biological processes in seagrass meadows are regulated by the exchange of m omentum, heat and mass between the surrounding water and the plants and thu s may strongly depend on the characteristics of water flow and turbulence. Comparisons of mean flow profiles, turbulence distribution and mixing in me adows of the seagrass Thalassia testudinum colonizing 2 hydrodynamically di fferent sites (wave-dominated and tide-dominated) suggest that the hydrodyn amic microclimate and consequently mixing within seagrass beds strongly dep end on the hydrodynamic forces (waves and currents) acting on the plants. U nidirectional flows deflect the water over the meadow (skimming flows), whi ch potentially leads to lower mixing between the water above and within the meadow. In contrast, waves cause the blades to move back and forth, increa sing the exchange between the water column and that within the meadow. Ther efore, the hydrodynamic conditions prevailing in the seagrass habitat (wave s, tides) change the pattern of flow attenuation and mixing within the vege tation.