LABARBERA, M. : Physical constraints in scallop swimming: take-off and swimming mechanics

Take-off from the substrate and swimming were recorded for the cold-temperate scallops Chlamys hastata (N=10), C. rubida (N=22), and Crassodoma gigantea (N=7) and the warm-temperate Argopecten irradians (N=43) using high speed video. The Chlamys species and Argopecten swim throughout their lives, but Crassodoma swims only as juveniles; adults are cemented to the substrate. Video recordings were analyzed to determine clap frequency, instantaneous accelerations, and average speed. Scallops ranged in height from 5-65 mm for the Chlamys species, 5-57 mm for Argopecten, and 26-45 mm for C. gigantea. Peak acceleration for all species was approximately 0.5 ms^-2; the largest and smallest individuals exhibited lower accelerations than intermediate-sized animals. Average swimming speed (integrated along the animal’s path) ranged from 10-40 cm/s. Larger animals achieved higher absolute swimming speeds, but relative speeds (shell heights/sec) were maximal in the smallest animals and declined linearly with increasing shell size. For all species, clap frequency was a linear function of shell height; C. gigantea was indistinguishable from the other species during its byssally-attached phase. Using published data for an additional seven species of scallops, a single function describes the relationship between shell height and clap frequency for all scallops, independent of phylogenetic relationships or environmental temperature. These data are the first measurements of acceleration during jetting for any scallop and the first quantitative description of swimming in juvenile Crassodoma.