STRATEGIES FOR LIFE IN FLOW - TENACITY, MORPHOMETRY, AND PROBABILITY OF DISLODGMENT OF 2 MYTILUS SPECIES

The attachment strength of sessile intertidal organisms is continuousl y challenged by the hydrodynamic forces generated by breaking waves. T his study explores mechanisms by which the attachment strength, or ten acity, can vary for one of the dominant competitors for space in this environment, the marine mussel. Tenacity was measured for 2 co-existin g mussel species, Mytilus californianus and Mytilus trossulus, either solitary or within a bed ( = bed mussels). The tenacity of M., califor nianus was higher than M. trossulus, due to increased byssal thread th ickness, and the tenacity of solitary mussels was higher than bed muss els, due to the presence of more byssal threads per mussel. These tena city measurements were coupled with modeled hydrodynamic forces to pre dict the probability of dislodgment due to wave action. For a given wa ter velocity, the predicted probability of dislodgment of M., californ ian us was lower than that of M. trossulus ,because the latter produce s relatively thinner threads (reducing tenacity) and a relatively more voluminous shell (increasing hydrodynamic loading). Compared to solit ary mussels, led mussels had a lower ,probability of dislodgment for a given water velocity (despite their lower tenacity) because they are subjected to relatively smaller hydrodynamic forces. These predictions are consistent with field observations that mussels typically form de nse aggregations and that M. trossulus rarely inhabits highly wave-exp osed shores.