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

Kelly Sutherland, University of Oregon, Oregon Institute of Marine Biology, Eugene, United States, Brad Gemmell, University of South Florida, Department of Integrative Biology, Tampa, United States, Sean Colin, Roger Williams University, Marine Biology and Environmental Science, Bristol, United States and Jack Costello, Providence College, Biology, Providence, United States
Abstract:
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.