ADVECTION AND ZOOPLANKTON FITNESS

Successful adaptation to the environment by zooplankton is constrained by the agents of mortality (starvation, predation) and losses due to advection. A fitness measure which explicitly includes risk of advecti ve loss is presented. The authors show that as horizontal current spee ds and vertical shear increase, the behavioral strategies that maximiz e fitness of zooplankton possessing different life history strategies are affected. For a Calanus finmarchicus-type life history, fitness is maximized by diel vertical migrations when advection risk in surface waters is low and by spending less time in the surface layers as flow rate increases. For a Paracalanus parvus-type life history, vertical m igration is postulated to occur as advective loss increases. The geogr aphic length scale of the habitat of residence also affects the optima l mode of habitat selection. In the Calanus case an abrupt change in t he optimal vertical migration pattern is postulated as a function of l ength scale of habitat and rate of advection.