The interrelationship of copepod fecundity and mortality

Abstract

The fecundity of copepod species that carry attached eggs is commonly assessed by the egg ratio (eggs female−1), whereas the fecundity of broadcast‐spawning copepods is assessed by measures of daily per capita rates of egg production. Variability in these measures, when corrected for temperature and allometric relationships with body size of adult females, is often assumed to reflect variability in food supply in nature and to thus provide an index of food limitation of population growth and of secondary production. We show that the measured fecundity of both brooding and broadcast‐spawning copepods is affected by the mortality rate of adult females. We recognize three reproductive stages of adult female copepods: prereproductive, reproductive, and postreproductive. Mortality affects realized fecundity by shifting the relative abundance levels in these stages. Changes in mortality rates can generate substantial temporal variations in measured fecundity, even for copepods that are unlimited by ambient food supply and reproduce at physiological maximum rates. To correct for the effects of mortality on realized fecundity, precise experimental determination of the reproductive schedule of adult females is needed, along with measures of mortality rates in nature.