Physical interactions between seaweed blades of Saccharina latissima and unidirectional turbulent flow were examined in an open-channel flume, focussing on flow velocities, drag force acting on a blade, and blade reconfiguration. The data reveal that seaweed blades adjust to high-energy flow conditions relatively quickly, efficiently reducing flow-induced drag via compaction, a mechanism of blade reconfiguration. The drag coefficient of blades of S. latissima varied between 0.02 and 0.07 over a range of mean flow velocities from 0.1 to 0.55 m/s. Both flow action and blade biomechanical characteristics influenced the blade dynamics, with the flow role being predominant in highly energetic conditions. The interaction mechanisms and their strength were found to be scale-dependent, with the combined effect of reduced mean flow velocity and enhanced turbulence in blade wakes. The thickness of the diffusive boundary layer, an important factor in nutrient uptake from the surrounding water, was estimated to be in the range from 0.010 to 0.067 mm. Mechanisms of blade adjustment to the flow and scale-dependent dynamic interactions between blades and turbulent eddies have direct implications for seaweed growth, acclimation, and survival. The estimates of the drag coefficient and the thickness of the diffusive boundary layer will be useful for the development of bio-physical models, environmental assessments, and design of seaweed farms.
The work described in this publication was undertaken during the Ph.D. study of Davide Vettori at the University of Aberdeen funded by a scholarship from the Northern Research Partnership, Scotland. The authors gratefully acknowledge: Peter Davies and Paul Mitchell for their support and guidance; David Attwood for his assistance during seaweed collection; Hamish Biggs for his assistance during seaweed collection and transport to the University of Aberdeen, and in setting up LED used to synchronise instruments; and Roy Gillanders and Benjamin Stratton for meticulous technical support. Many insightful comments provided by the Associate Editor Professor J. D. Ackerman and anonymous reviewer helped to improve the quality of
the fnal manuscript.
- Diffusive boundary layer
- Drag force
- Flow-vegetation interaction