Waves in Seagrass Systems: Review and Technical Recommendations

Abstract

Seagrasses are rooted flowering marine plants that provide a variety of ecosystem services to the coastal areas they colonize. Attenuation of currents and waves and sediment stabilization are often listed among these services. Although we have a reasonably good understanding of how currents affect seagrasses and vice-versa, less is known about interactions between waves and seagrasses, and standard methods for research on waves in seagrass systems have not yet been established. This report presents background information needed to inform and encourage further studies on waves in seagrass systems from both field and modeling perspectives. It reviews current knowledge of waves in seagrass systems, encompassing field and laboratory data as well as modeling efforts. It then describes various methods for measuring waves in seagrass colonized areas and modeling the dynamics of wave-seagrass interactions. Standardization of experimental designs, instrumentation, analyses, and modeling approaches to allow for ready comparison between studies is encouraged.

Wave Dissipation by Vegetation

“…The interaction of waves with vegetation can vary with relative depth (or wave period), and it is anticipated that vegetation will affect shallow-water waves more than deepwater waves because shallow waves tend to have larger velocities throughout the water column and near the bed. It is important to note that waves interact with the bottom based on relative depth, so waves with longer wave lengths become shallow-water waves and interact with the bottom at deeper depths (Koch et al 2006). Particle trajectories for shallow-water (a) and deepwater (b) waves (Dean and Dalrymple 1991).…”

“…This section reviews ongoing mechanisms and processes briefly at each of these scales of analysis and the resulting effects on wave attenuation. Complex feedback mechanisms also exist between the wave environment altering vegetation; however, these are beyond the scope of this review (See Koch et al 2006 for review).…”

“…The primary material property of interest is the rigidity or flexibility of the plant material, often reported as Young's modulus of elasticity (Ghisalberti andNepf 2002, Freeman et al 2000). Of particular interest in wave environments is the material density or specific gravity, which determines an individual's buoyancy and location in the water column (Koch et al 2006). Skin friction of plant material varies with leaf and stem conditions, and in some cases exposed roots also contribute (e.g., mangrove swamps).…”

Nonlinear hydrodynamics in a Mediterranean lagoon

“…Over the last decades, there have been global declines in seagrass abundance in many places in the world, and management decisions aimed at protecting and restoring submerged aquatic vegetation have been taken in many places (Fonseca et al, 1996;Koch et al, 2006;Pickerell et al, 2005;Van der Heide et al, 2007;Cardoso et al, 2008;Koch et al, 2009, Shafer andBergstrom, 2010;Vacchi et al, 2012). Of course, it is known that there are a lot of abiotic and biotic factors, which can affect the losses of seagrasses and their lack of recovery.…”

Response of Posidonia Oceanica to Wave Motion in Shallow-Waters - Preliminary Experimental Results

“…Posidonia Oceanica is present on rocky bottom rarely. Moreover the density of plants usually varies between 500 and 1,000 plants per square meter (Koch, 2006).…”