Interspecific differences in depth preference: regulation of larval transport in an upwelling system

Abstract

Dispersal is fundamental to understanding the ecology and evolution of species and effectively managing resources, but information on dispersal is rare for the vast majority of marine life that develops as miniscule larvae in the plankton. Until recent evidence to the contrary, it was widely suspected that larvae developing in productive upwelling regimes along eastern ocean margins are susceptible to cross-shelf transport by strong, dynamic currents and often are unable to replenish populations. We now show that interspecific differences in depth preference likely play a role in regulating differences in offshore migration from adult populations. Two open-coast species (Petrolisthes cinctipes and Pachygrapsus crassipes) did not undertake endogenously timed tidal vertical migrations but an estuarine species (Hemigrapsus oregonensis) did, which would facilitate seaward dispersal. Surprisingly, none of the 3 species undertook diel vertical migrations in the laboratory, even though all do in the field. Diel vertical migrations in marine and freshwater species elsewhere in the world are cued by light and reduce fish predation, but they may be cued by turbulence in upwelling regimes, thereby reducing transport from adult popula- tions. Thus, larvae of species that hatch in different locations and develop at different distances from the shore exhibit diverse larval swimming behaviors that regulate transport in dynamic upwelling regimes in previously undescribed ways, which has implications for population connectivity, local adaptation and resource management.