Hydrodynamics of Benthic Macrophytes in Waves Versus Currents

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Moving water can dislodge sessile marine organisms. Such physical disturbance can be important in structuring benthic communities. Sessile organisms range in stiffness from rigid corals to flexible macroalgae. The object of this investigation is to study how the flexural stiffness and size of planar, sessile organism (e.g. many macrophytes and invertebrate colonies) affect the hydrodynamic forces they experience in unidirectional currents and in waves (oscillating flow). Experiments using physical models in unidirectional and oscillating flow tanks will systematically quantify the relationship of an organism's size and stiffness to force and to local water velocities relative to the organism's surfaces. These experiments will be complemented by similar field measurements on real macroalgae and models. An example of the biological consequences of the relationship between size, stiffness, and hydrodynamic force will be explored by investigating the mechanical interactions between encrusting epiphytic bryozoans and the algal hosts they stiffen. This study is significant because it will provide basic rules about the consequences of size and flexibility to the vulnerability of sessile organisms to physical disturbance in wave-swept versus current-swept habitats.