Planktonic larval mortality rates are lower than widely expected

Fundamental knowledge of mortality during the planktonic phase of the typical marine life cycle is essential to understanding population dynamics and managing marine resources. However, estimating larval mortality is extremely challenging, because the fate of microscopic larvae cannot be tracked as they develop for weeks in ocean currents. We used a two-pronged approach to provide reliable estimates of larval mortality: (1) frequent, long-term sampling where the combination of larval behaviors and recirculation greatly reduces larval transport to and from the study area, and (2) an improved method of calculating larval mortality that consists of a vertical life table with a negative binomial distribution to account for the notorious patchiness of plankton. Larval mortality rates of our study species (barnacles and crabs) were <= 0.14 larvae/d, which produce survivorships over an order of magnitude higher than commonly determined for marine larvae. These estimates are reliable because they were similar for species with similar dispersal patterns. They are conservative because they were conducted in a highly advective upwelling system, and they may be even lower in other systems using our approach. Until other systems can be tested, our improved estimates should be used to inform future models of population dynamics and the evolution of life histories in the sea.