The effects of temperature and viscosity on the metachronal swimming of crustaceans

Abstract

Temperature changes as small as $3 ^\circ$C have been observed to significantly impact how self-propelled organisms move through their environment, especially for those inhabiting the transitional flow regime in which both viscous and inertial effects are important. Nonetheless, many oceanic species can successfully migrate across temperature changes in the order of $20 ^\circ $C, corresponding to $40 \%$ differences in viscosity, via metachronal propulsion, suggesting that this propulsion mechanism is resilient to drastic changes in water column properties. We investigate marsh grass shrimp (\textit{Palaemon vulgaris}) as a model organism to explore the combined physical and physiological effects on their locomotion at natural seasonal temperature extremes ($6^\circ - 20^\circ$C). Experimentally, we manipulate temperature and viscosity independently to isolate physical and physiological effects. We then use the shrimp morphology and gait data to inform a computational fluid dynamics parametric study to estimate the force-to-power ratios of varying viscosity and beat frequencies through naturally occurring extremes. Our research demonstrates that shrimp do not modify their gait parameters to naturally occurring viscosity changes, and their swimming performance is impacted by less than $9 \% $. The robustness of the metachronal gait is evidence of the ecological success of shrimp-like organisms in all climates, from the tropics to pole waters and inland freshwater