title: Drag reduction in wave-swept macroalgae: alternative strategies and new predictions.
abstract: OBJECTIVE
  Intertidal macroalgae must resist extreme hydrodynamic forces imposed by crashing waves. How does frond flexibility mitigate drag, and how does flexibility affect predictions of drag and dislodgement in the field?
  
  
  METHODS
  We characterized flexible reconfiguration of six seaweed species in a recirculating water flume, documenting both shape change and area reduction as fronds reorient. We then used a high-speed gravity-accelerated water flume to test our ability to predict drag under waves based on extrapolations of drag recorded at slower speeds. We compared dislodgement forces to drag forces predicted from slow- and high-speed data to generate new predictions of survivorship and maximum sustainable frond size along wave-swept shores.
  
  
  RESULTS
  Bladed algae were generally "shape changers", limiting drag by reducing drag coefficients, whereas the branched alga Calliarthron was an "area reducer", limiting drag by reducing projected area in flow. Drag predictions often underestimated actual drag measurements at high speeds, suggesting that slow-speed data may not reflect the performance of flexible seaweeds under breaking waves. Several seaweeds were predicted to dislodge at similar combinations of velocity and frond size, suggesting common scaling factors of dislodgement strength and drag.
  
  
  CONCLUSIONS
  Changing shape and reducing projected area in flow are two distinct strategies employed by flexible seaweeds to resist drag. Flexible reconfiguration contributes to the uncertainty of drag extrapolation, and researchers should use caution when predicting drag and dislodgement of seaweeds in the field.
authors.affiliation: Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Martone
authors.forename: Laurie
authors.initials: L
authors.lastname: Kost
authors.forename: Michael
authors.initials: M
authors.lastname: Boller
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D002140:California; D012624:Seaweed / Q000502:physiology*; D014872:Water Movements