CARRINGTON, E.: Predicting Disturbance to Mussel Beds: Physiological Response to a Variable Wave Climate

Mussels often dominate the mid-intertidal zone of temperate rocky coasts, forming dense beds that exclude other primary space holders. The rate at which large storms remove mussels from their substrate strongly influences the intertidal community, and several recent advances have been made in the prediction of disturbance by waves. One important physiological parameter in the prediction of dislodgment rates is the strength of mussel attachment relative to the force it encounters. For Mytilus edulis in Rhode Island, byssal attachment varies seasonally, with a two-fold increase in strength in winter compared to summer. Time series analysis of monthly samples (1998-2000) indicates attachment strength generally tracks seasonal fluctuations in wave height, suggesting that mussels can sense and respond to changes in their wave climate. However, the mechanical response to wave climate is not precise; during September and October (hurricane season), mussels remain weakly attached and are prone to major mortalities. Interestingly, reproductive condition also varies seasonally, peaking 3-4 months before attachment strength. This suggests that the ability of mussels to respond to the prevailing wave climate may be constrained energetically, as mussels trade-off between byssal thread production and gonad development. Thus it is important to consider not only a storm’s magnitude, but it’s timing relative to the cycle in attachment strength in order to accurately predict disturbance events. A better understanding of the causes of variable attachment strength is needed before we can make meaningful predictions of how long-term shifts in wave climates will affect mussels and their ability to influence community structure.