UC San Diego

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 advective loss is presented. The authors show that as horizontal current speeds and vertical shear increase, the behavioral strategies that maximize fitness of zooplankton possessing different life history strategies are affected. For a Calanus finmarchicus-type life history, fitness is maximized by did 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 migration is postulated to occur as advective loss increases. The geographic length scale of the habitat of residence also affects the optimal mode of habitat selection. In the Calanus case an abrupt change in the optimal vertical migration pattern is postulated as a function of length scale of habitat and rate of advection.