Age affects strain-rate dependence of the mechanical properties of kelp tissue

Premise:  The resistance of macroalgae to hydrodynamic forces imposed by ambient water motion depends in part on the mechanical properties of their tissues.  In wave-swept habitats, tissues are stretched (strained) at different rates as hydrodynamic forces constantly change.  Kelp have tissues of different ages, and mechanical properties of kelp tissue change with age.  However, the effects of age on the strain-rate dependence of the mechanical behavior of kelp tissues is unknown. 

Methods:  Using the kelp Egregia menziesii, we measured how high strain rate (simulating wave impingement) vs. lower strain rate (simulating wave surge) affected mechanical properties of frond tissues of various ages.  

Results:  Stiffness of tissues of all ages increased with strain rate, whereas extensibility was unaffected.  Strength and toughness of old tissue were unaffected by strain rate but increased with strain rate for young tissue.  

Conclusions:  Young tissue is weaker than old tissue, an...