Planktonic larval mortality rates are lower than widely expected

Abstract

TitlePlanktonic larval mortality rates are lower than widely expected Abstract. 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.

Nearshore Larval Retention and Cross-Shelf Migration of Benthic Crustaceans at an Upwelling Center

“…Moreover, the ability of larvae to regulate transport could have a large impact on dispersal and population connectivity and has been debated for decades. We recently determined that larvae occurred close to shore in persistent, strong upwelling on the Pacific Coast of the USA-rather than lost offshore as was widely expected (Morgan et al, 2009b(Morgan et al, ,c, 2011Morgan and Fisher, 2010;Fisher et al, 2014;Hameed et al, 2018)-and that larval mortality in the nearshore retention zone was much lower than previous estimates of larval mortality anywhere (White et al, 2014). We then demonstrated that larval behaviors enabling larvae to remain close to shore throughout development also enable them to settle near natal populations (Drake et al, 2013;Hameed et al, 2016).…”

Dispersal and population connectivity in the deep North Atlantic estimated from physical transport processes

“…Better estimates of dispersal and connectivity in the 572 deep sea will require more details about larval behavior and development at depth. In 573 addition, spatial variation in fecundity, mortality during the larval phase and larval 574 physiological tolerance needs to be included because they can influence dispersal and 575 population connectivity (Treml et al, 2012;White et al, 2014). …”

Inverse approach to estimating larval dispersal reveals limited population connectivity along 700 km of wave-swept open coast

“…One important consideration is that the mortality rate estimated by White et al [49] explicitly accounts for and excludes advection, while the observed settlement data include mortality as well as losses due to advection, which may contribute significantly to the mortality of open-coast invertebrate larvae [64]. By projecting the consequences of our dispersal kernel for metapopulation dynamics, we estimated the predicted connectivity among all subpopulations in the study.…”