Mortality of marine planktonic copepods: global rates and patterns

Using life history theory we make predictions of mortality rates in marine epi-pelagic copepods from field estimates of adult fecundity, development times and adult sex ratios. Predicted mortality increases with temperature in both broadcast and sac spawning copepods, and declines with body weight in broadcast spawners, while mortality in sac spawners is invariant with body size. Although the magnitude of copepod mortality does lie close to the overall general pattern for pelagic animals, copepod mortality scaling is much weaker, implying that small copepods are avoiding some mortality agent/s that other pelagic animals of a similar size do not. We compile direct in situ estimates of copepod mortality and compare these with our indirect predictions; we find the predictions generally match the field measurements well with respect to average rates and patterns. Finally, by comparing in situ adult copepod longevity with predation-free laboratory longevity, we are able to make the first global approximations of the natural rates of predation mortality. Predation and total mortality both increase with increasing temperature; however, the proportion that predation makes of total adult mortality is independent of ambient temperature, on average accounting for around ⁄3 to ⁄4 of the total.