Meeting Abstract

80.1  Sunday, Jan. 6  Indefatigable: Erect Coralline Alga Is Immune To Fatigue DENNY, MW*; MARTONE, PT; Stanford University; University of British Columbia mwdenny@stanford.edu

Intertidal organisms are subjected to intense hydrodynamic forces as waves break on shore. These repeated insults can cause an organism’s structural materials to fatigue and fail even though no single force would be sufficient to break the plant or animal. Indeed, Mach et al. (2011) found that mortality in the intertidal red alga Mazzaella flaccida was caused by fatigue rather than by the one-time imposition of extreme force. When pulled to 50% of one-time breaking stress, Mazzaella breaks after a few thousand cycles. One might suppose that erect coralline algae–composed of rigid calcified segments separated by genicula: small, flexible joints–would be even more susceptible to fatigue: strain is concentrated in the genicula. We tested this supposition by repeatedly loading fronds of Calliarthron cheilosporioides, a coralline alga common on wave washed shores in California. Loaded to 50% of its one-time breaking stress Calliarthron commonly survives more than a million cycles, with a record of 52 million. The maximum lifetime of Calliarthron is six years, during which it experiences only a small fraction of this number of stressful events. Thus, Calliarthron is immune to fatigue failure. We hypothesize that Calliarthron’s fatigue resistance is due to the microscale structure of its genicula. Each geniculum is a single layer of cells that are attached at their ends to the calcified segments but have minimal adherence to each other. This lack of adhesion allows each cell to act as a “crack stopper,” inhibiting the growth of fatigue cracks. Reference: Mach, KJ, Tepler SK, Staaf AV, Bohnhoff JC, and Denny MW. (2011) J. Exp. Biol. 214: 1571-1585.