Fragmentation in Seagrass Canopies Can Alter Hydrodynamics and Sediment Deposition Rates

Abstract

Seagrasses are valuable coastal ecosystems that protect the seabed from waves and currents. They are threatened by predominately anthropogenic activities which are causing their decline in many regions, often converting large continuous meadows into highly fragmented ones with gaps or bare sand interspersed within the meadows. To evaluate the impact fragmentation is having on the meadows’ capacity to attenuate waves, the hydrodynamics in four meadows with different fragmentation were studied by measuring wave velocity and turbulent kinetic energy. In our study area, as gap size increases, both the turbulent kinetic energy and wave velocity increase in the center of the gaps. However, although wave attenuation varied between the different fragmentation levels, no clear trend was found for wave attenuation or the level of fragmentation. Simply put, neither wave velocity nor turbulent kinetic energy presented significant trends with the fragmentation levels of the canopy on larger scales. Therefore, within the spatial and temporal limitation of this study, fragmentation on a landscape scale did not affect the hydrodynamics within the gaps. Furthermore, as with hydrodynamics, sedimentation rates also increased with gap size, but did not show differences at the landscape level with the fragmentation levels of the meadows.