COMMENT Calanoid copepods: linking lower-higher trophic levels by linking lower-higher Reynolds numbers

The copepods are said to be the most abundant multicellular animals on earth, with an estimated species number of 11 500+ (Humes 1994). The most typical form of planktonic copepods in the oceans is the calanoids, which makes up >?Or% of all net-collected zooplankton (e.g. Lalli & Parsons 1993). Why are the calanoids so abundant and successful? A clue to the answer to this question is the size (and the moving speed) of the calanoids, as shown in the life strategies of many animals (e.g. McMahon 1973, Schmidt-Nielsen 1984). The size of ca1anoi.d~ ranges roughly from 0.5 to 5 mm, and lies on the border that separates the aquatic habitats into 2 parallel worlds: the inertial and vlscous worlds (Purcell 1977; Fig. 1 ) . In the inertial world, the combat between prey and predators is primarily a matter of speed in escape and attack (Kerfoot 1978). By contrast, viscosity predominates over speed in the viscous world, where a moving object drags water and a water current drags objects. The inertial and viscous worlds are described by the Reynolds number (Re), which is the dimensionless ratio of inertial and viscous forces as follows: