Abstract
The colonial cnidarian, Nanomia bijuga, is highly proficient at moving in three-dimensional space through forward swimming, reverse swimming and turning. We used high speed videography, particle tracking, and particle image velocimetry (PIV) with frame rates up to 6400 s−1 to study the kinematics and fluid mechanics of N. bijuga during turning and reversing. 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). The maximum angular velocity of N. bijuga, 215 deg. s−1, exceeded that of many vertebrates with more complex body forms and neurocircuitry. Through the combination of rapid nectophore contraction and velum modulation, N. bijuga generated high speed, narrow jets (maximum = 1063 ± 176 mm s−1; 295 nectophore lengths s−1) and thrust vectoring, which enabled high speed reverse swimming (maximum = 134 ± 28 mm s−1; 37 nectophore lengths s−1) that matched previously reported forward swimming speeds. A 1:1 ratio of forward to reverse swimming speed has not been recorded in other swimming organisms. Taken together, the colonial architecture, simple neurocircuitry, and tightly controlled pulsed jets by N. bijuga allow for a diverse repertoire of movements. Considering the further advantages of scalability and redundancy in colonies, N. bijuga is a model system for informing underwater propulsion and navigation of complex environments.
Highlights
Planktonic marine organisms navigate three-dimensional space to acquire food, avoid predation and reproduce
Being colonial allows organisms with simple neurocircuitry and morphology to achieve complex movements and is of direct application to designing multi-jet vehicles that are adept at navigating the ocean
Turns in N. bijuga colonies were accomplished by pulsing of a single apical nectophore
Summary
Planktonic marine organisms navigate three-dimensional space to acquire food, avoid predation and reproduce. The presence of multiple jetting units that can be operated individually or simultaneously opens a wider array of swimming maneuvers than is available to organisms that have only one propulsive unit as in medusan jellyfish. Being colonial allows organisms with simple neurocircuitry and morphology to achieve complex movements and is of direct application to designing multi-jet vehicles that are adept at navigating the ocean. One of the appealing elements of pulsed jets is they allow for maneuvers in small spaces at low speeds more effectively than propellers [4]. The presence of multiple jets along the colony axis in N. bijuga can inspire new underwater vehicles that are streamlined (Figure 1a), effective at long-distance cruising, and highly maneuverable due to the strategic placement of jets along the colony axis to produce torque
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