Comparison of mechanical properties of four large, wave‐exposed seaweeds

Abstract

Seaweeds have a simple structural design compared to most terrestrial plants. Nonetheless, some species have adapted to the severe mechanical conditions of the surf zone. The material properties of either tissue sections or the whole stipe of four wave-exposed seaweeds, Durvillaea antarctica, D. willana, Laminaria digitata, and L. hyperborea, were tested in tension, bending, and torsion. Durvillaea has a very low modulus of elasticity in tension (E(tension) = 3-7 MN·m(-2)) and in bending (E(bending) = 9-12 MN · m(-2)), torsion modulus (G = 0.3 MN · m(-2)) and strength (σ(b)rk = 1-2 MN · m(-2)), combining a compliable and twistable stipe "material" with a comparatively high breaking strain (ε(brk) = 0.4-0.6). In comparison, the smaller stipes of Laminaria have a higher modulus of elasticity in tension (E(tension) = 6-28 MN·m(-2)) and in bending (E(bending) = 84-109 MN·m(-2)), similar strength (σ(brk) = 1-3 MN·m(-2)), and a higher torsion modulus (G = 0.7-10 MN·m(-2)), combined with a lower breaking strain (ε(brk) = 0.2-0.3) than Durvillaea. Time-dependent, viscoelastic reactions were investigated with cycling tests. The tested species dissipated 42-52% of the loading energy in tension through plastic-viscoelastic processes, a finding that bears important ecological implications. Overall, there seems to be no correlation between single material properties and the size or habitat position of the tested seaweed species.

Interspecific comparison of hydrodynamic performance and structural properties among intertidal macroalgae

“…Conversely, Dudgeon and Johnson observed greater reconfiguration in a stiff species (Mastocarpus) than in a more flexible species (Chondrus) (Dudgeon and Johnson, 1992). Harder et al observed a correlation between tissue stiffness and exposure (Harder et al, 2006), suggesting that lower stiffness bestows greater reconfiguration and survival.…”

“…However, the torsion of branches may be important for the compaction of blades. Thus, variation in torsion modulus among macroalgal species (Harder et al, 2006) may influence reconfiguration. Further, tissue stiffness in compression and tension may differ and influence bending of branches (Koehl and Wainwright, 1977;Gaylord and Denny, 1997).…”

“…Mechanical adaptations that increase the reconfiguration of macroalgae should be beneficial and may be reflected in a correlation between the solid-mechanical characteristics and hydrodynamic performance. Previous studies have examined this relationship in a theoretical and experimental approach in two-dimensional flow (Alben et al, 2002;Alben et al, 2004), have characterized algal solid mechanics but assumed hydrodynamic performance based on environmental exposure (Harder et al, 2006), or used model macroalgae to vary solid mechanical properties (Stewart, 2006). Here, we use an empirical analysis combining the direct quantification of reconfiguration (Boller and Carrington, 2006a) with beam theory to examine how morphology and tissue stiffness influence reconfiguration.…”

To bend a coralline: effect of joint morphology on flexibility and stress amplification in an articulated calcified seaweed

“…Delf, 1932;Koehl, 1986;Carrington, 1990;Dudgeon and Johnson, 1992;Friedland and Denny, 1995;Blanchette, 1997;Gaylord, 1997;Bell, 1999;Denny and Gaylord, 2002;Boller and Carrington, 2006;Harder et al, 2006). One unifying characteristic that has been thoroughly explored in these studies is flexibility.…”

Convergence of joint mechanics in independently evolving, articulated coralline algae

“…the energy absorbed before breaking) was calculated from the area under a stress-strain curve, with an alga achieving toughness by being very strong, very extensible, or both. This property has been widely reported for marine plant tissues (Koehl and Wainwright, 1977;Armstrong, 1988;Patterson et al, 2001;Harder et al, 2006); however, the biological significance is unclear (Denny and Gaylord, 2002;Denny and Hale, 2003). Finally, we explored whether any apparent differences in those properties among the three subfamilies could be attributed to differences in cellular structure or cell wall thickness.…”