Environmentally forced variability in larval development of Euphausia pacifica: Implications on larval survival and recruitment success in the Southern California Bight

In this dissertation I investigate the impact of the oceanographic environment on larval development and population dynamics of the euphausiid Euphausia pacifica, and its implications on recruitment success. Life-history models were utilized to determine those E. pacifica larval stages during which developmental variability has the greatest impact on larval survivorship and eventual recruitment success. The model's results illustrated that variability in stage-specific developmental or mortality rates during the egg, calyptopis I, and furcilia I--II stages has a disproportionate impact on recruitment. The location of egg release and oceanographic processes which affect the temperature-food environment of calyptopis I larvae should have a strong effect on larval population dynamics.;Additionally, indirect developmental pathways associated with furcilia I--II larvae provide a morphological indicator of those environmental conditions under which recruitment suffers.;Two cruises were conducted in the Southern California Bight to assess the impact of mesoscale oceanographic variability on E. pacifica larval population dynamics and recruitment. The vertical distribution of larvae was restricted to the warmer and more productive surface waters, as was the depth range of egg release. The distribution of calyptopis I larval stages reflected gradients in chlorophyll fluorescence. Spatial variability was evident in furcilia I--II developmental pathways. Indirect furcilia development was associated with cooler temperatures and did not appear to be impacted by chlorophyll conditions. Variability in larval stage-frequencies associated with physical-biological oceanographic conditions are indicative of varying developmental success and survivorship, and illustrate the importance of larval processes to eventual recruitment success.;Inverse modelling of vital demographic parameters was employed to evaluate the relative importance of larval developmental variability and spawning histories to stage-frequency distributions sampled in the field. Among-station variability in larval stage-frequency distributions was more likely associated with spatial variability in larval developmental or mortality rates than with that of egg inputs. Between-cruise differences in larval population demography, however, are highly consistent with temporal variability in onset of egg release and sampling during different points of a spawning pulse. Environmental forcing of developmental variability in E. pacifica impacted mesoscale patterns of larval development and population structure. Such environmental forcing certainly contributes to heterogeneity in the spatial-temporal distribution of recruitment.