Benefits of concurrent metachronal cycles as observed in Americamysis bahia

Studies of metachronal swimming in crustaceans have previously focused on organisms whose pleopods on the same abdominal segment beat in tandem with each other resulting in one, 5-paddle metachronal stroke. In contrast, the mysid shrimp Americamysis bahia’s pleopods on the same abdominal segment beat independently of each other resulting in a metachronal stroke comprised of two, 5-paddle metachronal cycles that are 180° out-of-phase with each other running the length of the body. Free-swimming A. bahia were recorded with high-speed cameras to obtain high-resolution data of pleopod kinematics and resulting swimming behavior. Although A. bahia primarily rely on their thoracic appendages for swimming, they occasionally use their pleopods to achieve swim speeds up to 12 body lengths per second. Time series of speed during one metachronal stroke in 5-paddle euphausiids show a periodic increase corresponding to the power stroke of the longest paddle. This phenomena is absent in A. bahia suggesting that more paddles in a metachronal stroke result in smoother swimming. A. bahia also achieve faster normalized swim speeds than euphausiids and analysis of non-dimensional parameters, including Strouhal number and advance ratio, indicate that pleopodal swimming in A. bahia is tuned to achieve normalized swim speeds greater than 9 body length per second.