Adaptive Significance of Large Size and Long Life of the Chaetognath Sagitta Elegans in the Arctic

Zooplankton of high latitudes generally develop more slowly, reach a large size, and live longer than related forms in warmer seas. Existing explanations are reviewed and a new one offered. Where generation length is set by marked seasonality of food supply, as in the arctic, high fecundity and associated large size and slow development may be selected for. It is shown from analysis of generation length, fecundity, and natural mortality of the chaetognath Sagitta elegans than its biennial life cycle in the eastern Canacian Arctic is of optimal length.