Applying flow tank measurements to the surf zone: Predicting dislodgment of the Gigartinaceae

Our understanding of how flow affects the survival of members of the Gigartinaceae has advanced considerably in recent years. In particular, methods have been developed that give phycologists a powerful tool with which to predict mechanistically the survival of wave-swept macroalgae. One limitation of such methods, however, is the lack of hydrodynamic data for macroalgae in surf-zone flows. The method instead relies upon the extrapolation of low-velocity flow tank measurements (< 3.5 m s–1) to velocities well beyond their measured range (10–20 m s–1). Such extrapolation is particularly tenuous for flexible organisms, such as macroalgae, that can reconfigure in flow. This study uses three members of the Gigartinaceae to evaluate two commonly used methods for extrapolation of flow tank data to high water velocities: one that allows for continued thallus reconfiguration at extreme water velocities and one that does not. Limitations of both models are evident and underscore the need for improved measures of force generation on macroalgae exposed to extreme flows. Additionally, the extent to which the mechanical design might influence life history traits of the Gigartinaceae is discussed.