Fig. 1. Schematic of the aquarium set-up for the laboratory experiments. (A) Top view of replicate tank. Six racks were attached to an aluminum semi-circle connected to a central pneumatic piston. A single flow level, high or low, was established in each tank by circulating the water with a trawling motor. Each rack was placed on the periphery of the tank to minimize flow gradients. (B) Side view of pneumatics. Drawer-slides were used as guides to maintain a linear displacement of the aluminum rack support and the individual racks. These slides were attached both to the rack support and the pneumatic support crossbeam. The pneumatic piston was attached to the aluminum rack support and displaced ±2.5 mm. The piston was forced to change directions when an upper or lower pneumatic button was activated. Air lines connected the buttons to the pistons and back to the regulator. (C) Side view of a single rack. Each rack supported four mussels, each with a different combination of acceleration and byssal loading. The inner support was attached to the aluminum semi-circle and vertically displaced ±2.5 mm. The outer support was attached to the bottom of the tank and held fixed throughout the experiment. The order of each treatment was randomized between racks. Accel, acceleration; Load, byssal load.