(Georgia Institute of Technology, 2022-05-02)
Ruszczyk, Melissa
An organism’s physical environment can dramatically affect an organisms’ behavior and morphological design. The Reynolds number represents the ratio between inertial and
viscous forces in a fluid environment. This study is concerned with the challenges crustaceous plankton face resulting from living in a low- and intermediate-Reynolds number
aquatic environment.
In the first part of this study, the freshwater copepod Hesperodiaptomus shoshone is
exposed to a Burgers vortex- a flow feature meant to mimic turbulent eddies found in an organism’s environment. Male and female copepods were exposed to four vortex intensity levels plus a negative control in either a horizontal or vertical orientation of the vortex axis.
Trajectory analysis of H. shoshone swimming behavior shows that this copepod changes its swimming behavior in response to vortex orientation and not vortex level- a notable difference from marine copepods exposed to the same flow feature. These results may be
linked to ecological and geographic differences between freshwater and marine copepods.
In the second part of this study, the pleopod synchrony in the mysid shrimp Americamysis bahia is quantified. Shrimp and krill beat their pleopods in an adlocomotory sequence,
creating a metachronal wave. Usually, pleopod pairs on the same abdominal segment beat in tandem with each other, resulting in one 5-paddle stroke. Americamysis bahia’s pleopods on the same abdominal segment beat independently from each other, resulting in two 5-paddle metachronal cycles that run ipsilaterally along the body, 180° out of phase with each other. High-speed recordings of A. bahia stroke kinematics reveal how this mysid changes its stroke amplitude, beat frequency, and inter-appendage phase lag to achieve high
speeds. Trends with Strouhal number and advance ratio suggest that the stroke kinematics of metachrony in A. bahia are tuned to achieve large normalized swimming speeds.
In the third part of this study, stroke kinematics in Pacific krill, Euphausia pacifica, are quantified for the first time. Euphaisia pacifica (1-3cm body length) achieve similar swimming modes as the larger E. superba (4-6cm body length) through a different set of stroke kinematics. To better understand the relationship between stroke kinematics, resulting swimming mode, and length scale, these data are used in tandem with previously published stroke kinematics of other 5-paddle metachronal swimmers, including mysid shrimp and stomatopods, to identify broad trends across species and length scale in metachrony. Principle component analysis (PCA) reveals trends in stroke kinematics, Reynolds number, and swimming mode as well as variation among taxonomic order. Additionally, uniform phase lag, i.e. when the timing between power strokes of all adjacent pleopods is equal, in 5-paddles systems is achieved at different Reynolds numbers for each swimming mode, which highlights the importance of taking into consideration stroke kinematics, length scale, and resulting swimming mode in bio-inspired design applications.