title: Divergent growth strategies between red algae and kelps influence biomechanical properties.
abstract: OBJECTIVE
  Morphology and material properties are the main components of the mechanical design of organisms, with species groups developing different optimization strategies in the context of their physical environment. For intertidal and subtidal seaweeds, possessing highly flexible and extensible tissues allows individuals to bend and reconfigure in flow, thereby reducing drag. Previous research has shown that aging may compromise these qualities. Tissue age increases with distance from the blade's meristem, which differs in its position on kelps and red algae. Here, we assess whether longitudinal patterns of blade material properties differ between these two algal groups according to tissue age.
  
  
  METHODS
  We performed tensile tests on tissues samples excised from various positions along the extent of blades in nine kelp species (basal growth) and 15 species of red algae (apical growth).
  
  
  RESULTS
  We found that older tissues were less flexible and extensible than younger tissues in all species tested. As predicted, tissue near the basal meristem in kelp was more flexible and extensible than older tissue at the blade's distal end. The opposite pattern was observed for red algae, with the most flexible and extensible tissues found near the apical meristem at the distal ends of blades.
  
  
  CONCLUSIONS
  We propose that divergent patterns in the distribution of material properties along blades may have different consequences for the performance of kelps and red algae. The positioning of younger tissues at the blade base for kelps may enable these species to attain larger body sizes in wave-swept habitats.
authors.affiliation: Department of Resource and Environmental Management, Simon Fraser University, 622 Strand Hall Annex 8888 University Dr. Burnaby, B.C. Canada V5A 1S6 Hakai Institute, PO Box 309, Heriot Bay, B.C. Canada V0P 1H0 kkrumhan@sfu.ca.
authors.forename: Kira A
authors.initials: KA
authors.lastname: Krumhansl
authors.affiliation: Hakai Institute, PO Box 309, Heriot Bay, B.C. Canada V0P 1H0 Department of Zoology, University of British Columbia, 6270 University Blvd. Vancouver, B.C. Canada V6T 1Z4.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Demes
authors.affiliation: Department of Biology and Friday Harbor Laboratories, University of Washington, 620 University Road. Friday Harbor, WA USA 98250.
authors.forename: Emily
authors.initials: E
authors.lastname: Carrington
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd. Vancouver, B.C. Canada V6T 1Z4.
authors.forename: Christopher D G
authors.initials: CD
authors.lastname: Harley
mesh_terms: D001696:Biomechanical Phenomena; D044423:Kelp / Q000254:growth & development*; D000461:Rhodophyta / Q000254:growth & development*
keywords: Laminariales; Rhodophyta; biomechanics; growth strategy; kelp; material properties; red algae