A vertical life table approach to zooplankton mortality estimation

Zooplankton mortality is commonly estimated from time series of abundances (horizontal life table approach) with the assumption that transport processes are in the marine environment. We provide equations appropriate for analysis of stage distributions in zooplankton samples at a single time (vertical life table approach) that, in certain circumstances, facilitate mortality estimation without requiring time series of abundances. A primary assumption is that daily recruitment to a particular stage should not be characterized by a strong upward or downward trend. To improve the accuracy of parameter estimates, however, knowledge about such trends may be taken into account. The accuracy and precision of mortality estimation were assessed with an individual-based simulation model. Results obtained from application of the vertical approach to the copepod Pseudocalanus newmani are comparable to those obtained independently by a horizontal method. We conclude that the vertical approach may provide mortality estimates under conditions in which horizontal techniques are inappropriate. In contrast to estimates obtained with horizontal techniques, vertical estimates represent snapshots of the population.