Ec. Bell et Jm. Gosline, MECHANICAL DESIGN OF MUSSEL BYSSUS - MATERIAL YIELD ENHANCES ATTACHMENT STRENGTH, Journal of Experimental Biology, 199(4), 1996, pp. 1005-1017
The competitive dominance of mussels in the wave-swept rocky intertida
l zone is in part due to their ability to maintain a secure attachment
. Mussels are tethered to the substratum by a byssus composed of numer
ous extracellular, collagenous threads secreted by the foot. Each byss
al thread has three serially arranged parts: a corrugated proximal reg
ion, a smooth distal region and an adhesive plaque, This study examine
s the material and structural properties of the byssal threads of thre
e mussel species: Mytilus californianus, M. trossulus, and M. gallopro
vincialis, Tensile tests in general reveal similar material properties
among species: the proximal region has a lower initial modulus, a low
er ultimate stress and a higher ultimate strain than the distal region
, The distal region also yields at a stress well below its ultimate va
lue, In whole thread tests, the proximal region and adhesive plaque ar
e common sites of structural failure and are closely matched in streng
th, while the distal region appears to be excessively strong. We propo
se that the high strength of the distal region is the byproduct of a m
aterial designed to yield and extend before structural failure occurs.
Experimental and theoretical evidence is presented suggesting that th
read yield and extensibility provide two important mechanisms for incr
easing the overall attachment strength of the mussel: (1) the reorient
ation of threads towards the direction of applied load, and (2) the 'r
ecruitment' of more threads into tension and the consequent distributi
on of applied load over a larger cross-sectional area, thereby reducin
g the stress on each thread. This distal region yield behavior is most
striking for M. californianus and may be a key to its success in extr
eme wave-swept environments.