Hydrodynamics of Swimming and Maneuvering with Multiple Jets by a Colonial Siphonophore

The siphonophore Nanomia bijuga first gained the attention of oceanographers because it undertakes long vertical migrations on a diel basis and, owing to the gas-filled pneumatophore, is an important component of the sound scattering layer in much of the worlds’ oceans. In addition to long-distance migrations, N. bijuga is also capable of responding to stimuli by executing rapid maneuvers in three-dimensional space, including turning and reversing. High-speed, high-resolution microvideography, particle image velocimetry and particle tracking revealed that integration of nectophore and velum kinematics allow for a high-speed (maximum ∼1 m s−1), narrow (1–2 mm) jet and rapid refill, as well as a 1:1 ratio of jetting to refill time. N. bijuga achieved turns with high maneuverability (mean length-specific turning radius, R/L=0.15± 0.10) and agility (mean angular velocity, ω=104 ± 41 deg. s-1), exceeding that of many vertebrates with more complex body forms and neurocircuitry. Thrust vectoring enabled high speed reverse swimming (maximum=134 ± 28 mm s-1; 37 nectophore lengths s-1) that matched forward swimming speeds. N. bijuga is a highly effective swimmer and a model system for understanding structure-fluid interactions in multi-jet locomotion. Our upcoming studies using 3-D videography in the ocean will further our understanding of coordinated pulsed jets, and elucidate design principles optimized by nature.