A VERTICAL LIFE TABLE APPROACH TO ZOOPLANKTON MORTALITY ESTIMATION

Zooplankton mortality is commonly estimated from time series of abunda nces (horizontal life table approach) with the assumption that transpo rt processes are in the marine environment. We provide equations appro priate for analysis of stage distributions in zooplankton samples at a single time (vertical life table approach) that, in certain circumsta nces, facilitate mortality estimation without requiring time series of abundances. A primary assumption is that daily recruitment to a parti cular stage should not be characterized by a strong upward or downward trend. To improve the accuracy of parameter estimates, however, knowl edge about such trends may be taken into account. The accuracy and pre cision of mortality estimation were assessed with an individual-based simulation model. Results obtained from application of the vertical ap proach to the copepod Pseudocalanus newmani are comparable to those ob tained independently by a horizontal method. We conclude that the vert ical approach may provide mortality estimates under conditions in whic h horizontal techniques are inappropriate. In contrast to estimates ob tained with horizontal techniques, vertical estimates represent snapsh ots of the population.