Swimming of Planktonic Cyclops Species (Copepoda, Crustacea): Pattern, Movements and Their Control

Abstract

The zooplankton of lakes and seas consists for the most part of copepods, some species grazing phytoplankton and some living as carnivores, hunting other copepods. Animals of the order Cyclopoida are between 0. 05 and 0. 3 cm long and show a very distinct jerky (hop and sink) swimming pattern, using an average of one powerstroke per second. This gives them a mean speed of 0. 1 to 0. 5 cm/sec so that their Reynolds number ranges from 1 to 50. Storch (1929) filmed the sequence of movements of the four ventrally situated pairs of legs during a powerstroke and found a 4-3-2-1 metachronical pattern. One stroke of all the legs together brings them back to the original position (ventral, front), supposedly leaving the animal with a forward velocity component. The decelerating phase of one hop has been used by Vlymen (1970) to calculate the drag for one copepod species, for which he found the energy expended in swimming to be only 0. 3% of the metabolic energy consumption. In order to avoid an encounter with a predator, Cyclops display an escape reaction, swimming up to 35 cm/sec for about one second. This translates to about 120 powerstrokes per second. In this speed range flapping of the abdomen is more effective (Re ~ 500), but requires more energy.