The Kinematics of Swimming and Relocation Jumps in Copepod Nauplii

Abstract

Copepod nauplii move in a world dominated by viscosity. Their swimming-by-jumping propulsion mode, with alternating power and recovery strokes of three pairs of cephalic appendages, is fundamentally different from the way other microplankters move. Protozoans move using cilia or flagella, and copepodites are equipped with highly specialized swimming legs. In some species the nauplius may also propel itself more slowly through the water by beating and rotating the appendages in a different, more complex pattern. We use high-speed video to describe jumping and swimming in nauplii of three species of pelagic copepods: Temora longicornis, Oithona davisae and Acartia tonsa. The kinematics of jumping is similar between the three species. Jumps result in a very erratic translation with no phase of passive coasting and the nauplii move backwards during recovery strokes. This is due to poorly synchronized recovery strokes and a low beat frequency relative to the coasting time scale. For the same reason, the propulsion efficiency of the nauplii is low. Given the universality of the nauplius body plan, it is surprising that they seem to be inefficient when jumping, which is different from the very efficient larger copepodites. A slow-swimming mode is only displayed by T. longicornis. In this mode, beating of the appendages results in the creation of a strong feeding current that is about 10 times faster than the average translation speed of the nauplius. The nauplius is thus essentially hovering when feeding, which results in a higher feeding efficiency than that of a nauplius cruising through the water.

Choreographed swimming of copepod nauplii

“…Experimental data for A. tonsa indicate a backward displacement of approximately 33% of forward movement, which is greater than that observed in copepod nauplii using three pairs of appendages (approx. 20%; this study, [24]), which is consistent with model results (approx. 22%, second cycle, figure 7a).…”

Feeding capabilities and limitations in the nauplii of two pelagic estuarine copepods, Pseudodiaptomus marinus and Oithona davisae

“…Second, the size and morphology of feeding appendages differs between adults and nauplii (Fernandez 1979;Borg et al 2012). Adults have the full suite of feeding and swimming appendages (Mauchline et al 1998).…”

“…Finally, adults and nauplii of some copepod species can also have different feeding and swimming behaviors, which can result in differences in feeding efficiency (Kiørboe 2010;Borg et al 2012). For example, Pseudodiaptomus spp.…”

Lepeophtheirus salmonis (Krøyer, 1837): second nauplius and copepodid locomotor appendages, surface areas and possible appendage functions

“…The entire surface of area of all three naupliar appendages was measured since these appendages participate to some degree in movement (Andersen Borg et al, 2012). With copepodids, the thoracic legs are the primary propulsive appendages, the antennules, antennae, oral appendages and maxillipeds functioning as sensory or attachment stmctures.…”

“…However, mobility and maintaining suitable depth during the planktonic phase are important not only for dispersal but also maintaining suitable position, escaping from predators, and locating a host (e.g., Heuch & Karlsen, 1997). Although naupliar swimming has been termed "swimming-byjumping" (Andersen Borg et al, 2012) and Gravil (1996) used the term "hop and sink" for movement of all three planktonic stages of L. salmonis, differences in body shape, appendage nature and appendage display suggest potential differences in locomotor appendage use. The nauplius body is a single unit, oval in both plan view and cross section, and bears three pairs of appendages (antennules, antennae, mandibles) that project from the anterior third of the body.…”