TURBULENCE-INDUCED CONTACT RATES OF PLANKTON - THE QUESTION OF SCALE

Modelling encounter rates between planktonic predators and prey in tur bulent waters requires an estimate of a spatial scale. One spatial sca le proposed in the literature based on prey concentration is shown to be systematically inconsistent and its use is shown to imply that plan kton sampling methodology can bias encounter rate estimates in turbule nt situations. We show that a scale based on the predator's reactive d istance is more appropriate, as it has clear theoretical support, and is consistent with other mathematical treatments of encounter problems . Applying the reactive distance as the length scale produces encounte r rates for small (e.g. 4 to 10 mm) fish larvae 2- to 3-fold lower tha n those using prey separation distance.