Death by small forces: A fracture and fatigue analysis of wave-swept macroalgae

Katharine J. Mach, Benjamin B. Hale, Mark W. Denny, Drew V. Nelson

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


Wave-swept macroalgae are subjected to large hydrodynamic forces as each wave breaks on shore, loads that are repeated thousands of times per day. Previous studies have shown that macroalgae can easily withstand isolated impositions of maximal field forces. Nonetheless, macroalgae break frequently. Here we investigate the possibility that repeated loading by sub-lethal forces can eventually cause fracture by fatigue. We determine fracture toughness, in the form of critical strain energy release rate, for several flat-bladed macroalgae, thereby assessing their resistance to complete fracture in the presence of cracks. Critical energy release rates are evaluated through single-edge-notch, pull-to-break tests and single-edge-notch, repeated-loading tests. Crack growth at sub-critical energy release rates is measured in repeated-loading tests, providing a first assessment of algal breakage under conditions of repeated loading. We then estimate the number of imposed waves required for unnotched algal blades to reach the point of complete fracture. We find that, if not checked by repair, fatigue crack growth from repeated sub-lethal stresses may completely fracture individuals within days. Our results suggest that fatigue may play an important role in macroalgal breakage.

Original languageEnglish (US)
Pages (from-to)2231-2243
Number of pages13
JournalJournal of Experimental Biology
Issue number13
StatePublished - Jul 2007
Externally publishedYes


  • Breakage
  • Fatigue
  • Fracture mechanics
  • Macroalgae
  • Seaweed

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science


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