Meeting Abstract

S1-1.6  Jan. 4  Waves drag down macroalgae BOLLER, M.L.; Hopkins Marine Station of Stanford University

Vogel coined the term “reconfiguration” to describe the hydrodynamic process by which a flexible organism changes shape in response to the hydrodynamic forces imposed upon it. Reconfiguration is important to marine macroalgae in that it reduces the magnitude of hydrodynamic forces and decreases the risk of dislodgement and/or fragmentation; reconfiguration has been said to be a “prerequisite for survival” for some macroalgae. However, our understanding of the mechanisms of reconfiguration in the intertidal zone is limited because this complex solid mechanical/hydrodynamic process is almost impossible to directly observe in the field and difficult to replicate in the lab. In this study, reconfiguration in intertidal macroalgae was examined in two laboratory setups: a medium-speed recirculating flow tank and a high-speed gravity flume, which together encompass a range from 0.1 to >10 m s-1. A recently proposed “reconfiguration drag model” was fit to the medium-velocity data and used to predict drag at high velocities. This model separates the changes in frontal area and drag coefficient, potentially allowing for more accurate extrapolation than previously possible. High-speed measurements obtained from the gravity flume served as a test of the model. Results indicate that the reconfiguration model effectively characterizes drag when a sufficient velocity range (e.g. 1 to 6 m s-1) is examined and that velocity dependent effects of reconfiguration must be accounted for when extrapolating from low velocities. Combined with measurement of macroalgal tenacity, this model should make better predictions of survival on wave exposed shores.