| Marine mussels are dominant space competitors in the rocky intertidal, forming dense aggregations under a wide range of hydrodynamic conditions. Disturbances in mussel beds result in important successional processes that structure the ecosystems in which mussels can be found. The mussels' successful monopolization of space depends on their use of byssal fibers to secure themselves to their surroundings.; Mussels use byssal threads to attach themselves to surrounding substrata forming dense aggregations in the rocky intertidal. The matrix of byssal interconnections that are maintained among aggregation participants provide two distinct reservoirs of resistance to dislodgement: an active component made of threads produced by an individual, and a passive component made of threads from neighboring animals. Among aggregation participants, the passive component accounted for nearly 50% of total attachment strength.; The failure mechanics of the byssal organ is important to how disturbances start and under what circumstances. Using a Portable Materials Testing Device (PMTD), we are able to extract mussels from their aggregations in the field, measuring the instantaneous forces occurring during removal in summer and fall adapted mussels. Summer adapted mussels were more extensible and had piecewise byssal failure, with small clusters of threads failing throughout the profile. Fall adapted mussel byssus was stiffer, and exhibit catastrophic failure. The fracture mechanics suggest that mussels are less sensitive to large wave events than to chronic moderate to high wave stress.; Byssal threads connecting animals to one another help dissipate impinging hydrodynamic forces. Loss of one or more mussels not only creates a hole in the bed, but also reduces the byssal support of the neighboring animals with which the lost individual(s) interacted. We empirically measured several fundamental parameters of interaction within a mussel bed, and then used them to assemble a computer model of aggregating mussels. Patches of animals that are more strongly connected to one another than to their neighbors describe the internal structure of the model aggregation. Boundaries between these patches demark lines where disturbance is less likely to cross---like a precut sheet of stamps. |
