S1-1.8 Jan. 4 Flow Modification: Musseling Around the Flow THOMPSON, S.B.*; MOESER, G.M.; COUTTS, L; CARRINGTON, E; CSU Fresno; Univ. of Washington; Univ. of Richmond; Univ. of Washington firstname.lastname@example.org
Mussels are an important species in many marine habitats, providing food, filtering water, and acting as a home for many species. Mussels attach to various substrates with byssal threads produced by the foot. Moeser et. al. (2006) observed that thread production is limited by the ability of the foot to protrude into flow, and placed this physiological threshold at ~18 cm/s for solitary Mytilus edulis. Given that flows on wave swept shores are routinely two orders of magnitude higher (e.g. 35 m/s), it is unclear when mussels can produce threads on exposed coasts. This study evaluates the extent to which mussel aggregations (or beds) reduce extreme flows, thereby facilitating thread production. An Acoustic Doppler Velocimeter (ADV) was used to measure water velocities in mussel beds of M. galloprovincialis and M. trossulus in a flume and in the field. Video was also used for particle tracking to calculate velocities within 1 cm of the bottom. Flow velocities found in the bed were greatly reduced, less than 6% of freestream velocity in lab trials, and 0.5% of freestream in the field. When examined lengthwise along the bed, velocities decreased dramatically with increasing distance from the front of the bed, plateauing at 20 cm and beyond. While an analysis of small gaps (3-12 cm diameter) in a mussel bed showed an increase in velocity with increasing gap size, flow reduction provided by the neighboring bed was nonetheless substantial (< 13% of freestream). Overall, the magnitude of the flow reduction observed in the bed is sufficient for individual mussels to produce new byssal threads at freestream velocities that exceed their physiological threshold, even on exposed wave-swept coasts.