Abstract
Calanoid copepods have two swimming gaits, namely cruise swimming that is propelled by the beating of the cephalic feeding appendages and short-lasting jumps that are propelled by the power strokes of the four or five pairs of thoracal swimming legs. The latter may be 100 times faster than the former, and the required forces and power production are consequently much larger. Here, we estimated the magnitude and size scaling of swimming speed, leg beat frequency, forces, power requirements, and energetics of these two propulsion modes. We used data from the literature together with new data to estimate forces by two different approaches in 37 species of calanoid copepods: the direct measurement of forces produced by copepods attached to a tensiometer and the indirect estimation of forces from swimming speed or acceleration in combination with experimentally estimated drag coefficients. Depending on the approach, we found that the propulsive forces, both for cruise swimming and escape jumps, scaled with prosome length (L) to a power between 2 and 3. We further found that power requirements scales for both type of swimming as L3. Finally, we found that the cost of transportation (i.e., calories per unit body mass and distance transported) was higher for swimming-by-jumping than for cruise swimming by a factor of 7 for large copepods but only a factor of 3 for small ones. This may explain why only small cyclopoid copepods can afford this hydrodynamically stealthy transportation mode as their routine, while large copepods are cruise swimmers.
Highlights
The swimming of pelagic copepods is based on the principle of rowing strokes with oar-like limbs
The anatomy of the body structure is directly related to the way of swimming, and copepods are divided into two main groups: the ancient Gymnoplea and the more recent Podoplea [1,2]
Since even modern cameras do not allow for long-term recordings of animal activity, the copepod escape reaction may be synchronized with video records by various external means of stimulation, such as short, weak electrical pulses [30,31] or photic and hydrodynamic stimuli [19,20,58]
Summary
The swimming of pelagic copepods is based on the principle of rowing strokes with oar-like limbs. Storch [14] may have been the first to use a high-speed movie camera at 120 frames per second to study the jumping behavior of freshwater cyclopoid copepods He described the metachronal strokes of the thoracic legs of Cyclops scutifer during avoidance response. >500 body lengths per second, and they provided detailed descriptions of the movement of the feeding appendages and swimming legs during cruise swimming and jumps [7,15,16,17,18,19,20,21,22] These high resolution observations of swimming speeds and appendage kinematics provided the basis for estimations of the force production and energetics of copepod propulsion [23,24,25,26,27,28]. Subscripts cr cruising, free att attached, tethered to force sensor d drag cr cruising, free escape jump d esc drag kick escape jump kick, jump esc kick kick, jump max maximal max mean maximal mean mean mean min minimal min minimal propulsion p p propulsion stroke phase st st stroke phase
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