Hydrodynamics and energetics of jumping copepod nauplii and copepodids

Abstract

Within its life cycle, a copepod goes through drastic changes in size, shape and swimming mode. In particular, there is a stark difference between the early (nauplius) and later (copepodid) stages. Copepods inhabit an intermediate Reynolds number regime (between ~1 and 100) where both viscosity and inertia are potentially important, and the Reynolds number changes by an order of magnitude during growth. Thus we expect the life stage related changes experienced by a copepod to result in hydrodynamic and energetic differences, ultimately affecting the fitness. To quantify these differences, we measured the swimming kinematics and fluid flow around jumping Acartia tonsa at different stages of its life cycle, using particle image velocimetry and particle tracking velocimetry. We found that the flow structures around nauplii and copepodids are topologically different, with one and two vortex rings, respectively. Our measurements suggest that copepodids cover a larger distance compared to their body size in each jump and are also hydrodynamically quieter, as the flow disturbance they create attenuates faster with distance. Also, copepodids are energetically more efficient than nauplii, presumably due to the change in hydrodynamic regime accompanied with a welladapted body form and swimming stroke.

Quiet swimming at low Reynolds number

“…In the follow ing when plotting the velocity field we use the length scale a and the velocity scale u = F/(8npta). Figure 3 shows the velocity fields in the xz plane for a = 1, a = 0.1, and a = The predicted flow fields for low a values correspond qualitatively with the flow fields measured recently using particle image velocimetry for A. tonsa nauplii [27] and P intermedins [20]. Also, the stagnation point on the positive z axis and the two large lateral whirls in the velocity field in the a = 1 force configuration are found in the average velocity field observed around the breast stroke swimming C. reinhardtii [15].…”

Choreographed swimming of copepod nauplii

“…This would be particularly true for larger nauplii (L ¼ 170-260 mm) swimming at Re . 7 as calculated by Wadhwa et al [27]. Even in the case of B. similis nauplii, especially for the longer displacements in any one power stroke, the peak displacement was reached significantly after that predicted by the model based on observed appendage movement, which suggests the animals were carried forward by momentum ( figure 7a).…”

A Review of Planar PIV Systems and Image Processing Tools for Lab-On-Chip Microfluidics

“…Acartia Tonsa ( Figure 15 a) is known to pull double-breaststrokes using the first two pairs of its appendages during the early stage of their life cycle [ 29 ]. In an experiment performed at DTU [ 29 , 44 ], a long-distance 2CµPIV system was used to take measurements around a ~220-μm-long individual. A low-power, continuous-wave infrared laser (Oxford Lasers Ltd., Didcot, UK, 808 nm wavelength) was used for illumination.…”

“…In particular, research is focused on the design of magnetotactic biomicrofluidics [ 23 , 24 , 25 ], biologically-inspired micro propulsion systems [ 26 , 27 ], and programmable self-assembling micro-systems [ 28 ]. As a consequence, the importance of research efforts put on the swimming behavior and hydrodynamics of small marine organisms using flagella and appendages [ 29 , 30 , 31 ] have increased. The flow physics in micro scales has a direct effect on the locomotion efficiency, as the flow around the micro-swimmers are dominated by viscous forces.…”