A Model of Rowing Propulsion and the Ontogeny of Locomotion in <i>Artemia</i> Larvae

Abstract

Newly hatched Artemia larvae use one pair of limbs to locomote. During development they gradually add additional limbs along the elongating trunk. As larvae grow, body length increases from about 0.4 mm to 4 mm, mean swimming speed increases from 1.8 mm s-1 to 9.9 mm s-1, and frequency of antennal beat decreases from 9.5 to 6.7 Hz. As new limbs are added, they become active in the metachronal rhythm of pre-existing limbs. The body velocity oscillates as early larvae swim; later larvae swim without a cyclic acceleration and deceleration of the body. The change in the pattern of swimming is correlated with the addition of propulsors and a transition in the relative importance of viscous and inertial effects that determine the propulsion in subsequent stages. Reynolds number (based on body length) increases from 2 to 37. A theoretical analysis of rowing propulsion at these intermediate Reynolds numbers shows that initial development of new limbs in Artemia larvae is unimportant for propulsion. Rowing propulsion at the low Reynolds numbers is drag-based; as Reynolds number increases, inertial effects become more important, and unsteady forces on the body become significant in the balance between limb and body. A glide of the body develops at the end of the powerstroke, and relative limb velocity changes.