Swim and fly: escape strategy in neustonic and planktonic copepods

Copepods can respond to predators by powerful escape jumps that in some surface-dwelling forms may propel the copepod out of the water. We studied the kinematics and energetics of submerged and out-of-water jumps of two neustonic pontellid copepods, Anomalocera patersoni and Pontella mediterranea, and one pelagic calanoid copepod, Calanus helgolandicus (euxinus).

We show that jumping out of the water does not happen just by inertia gained during the copepod's acceleration underwater, but also requires the force generated by the thoracic limbs when breaking through the water's surface to overcome surface tension, drag and gravity. The timing of this appears to be necessary for success.

At the moment of breaking the water interface, the instantaneous velocity of the two pontellids reached 125 cm s-1, while their maximum underwater speed (115 cm s-1) was close to that of similarly sized C. helgolandicus (106 cm s-1). The average specific power produced by the two pontellids during out-of-water jumps (1700-3300 W kg-1 muscle mass) was close to that during submerged jumps (900-1600 W kg-1 muscle mass) and, in turn, similar to that produced during submerged jumps of C. helgolandicus (1300 W kg-1 muscle mass).

The pontellids may shake off water adhering to their body by repeated strokes of the limbs during flight, which leads to a slight acceleration in the air. Our observations suggest that out-of-water jumps of pontellids are not dependent on any exceptional ability to perform this behavior but have the same energetic cost and are based on the same kinematic patterns and contractive capabilities of muscles as those of copepods swimming submerged.