Impacts of changing ocean circulation, temperature, and food supply on larval recruitment of purple sea urchins in Southern California: A biophysical modeling study

Changes in ocean conditions among years and across decades can alter populations in marine ecosystems. This study evaluates the impact of changing ocean conditions on larval recruitment of purple sea urchins in the Southern California Bight using 3D biophysical modeling, surface chlorophyll, and recruitment data. The influence of circulation, temperature, and food supply on larval recruitment is quantified using five modeled variables, larval dispersal distance, larval source location, larval food supply, and temperature exposure for larvae and adults, which are derived for 18 years and five larval recruitment sites. Sensitivity testing of the variables to different plankton larval durations (PLDs), larval behaviors, and nearshore retention is performed. All variables are found to be relatively insensitive to changes in PLD greater than 26 days. Larval dispersal distance and source location, representing changes in circulation, are found to be more sensitive to larval behavior and nearshore retention than larval food supply and temperature exposure for larvae and adults. All variables are statistically compared to recruitment field data. Temperature exposure for adults during the fall reproductive season is found to be a strong driver of larval recruitment while temperature exposure for larvae during the spring recruitment season is not. Food supply is not found to be a driver of larval recruitment. Circulation is found to be a driver of larval recruitment if larvae have behavior that reduces their dispersal distance, allowing them to come from source sites near to the recruitment sites. Overall, we hypothesize that larval behavior which reduces dispersal improves recruitment and that the timing of recruitment and reproduction can predict the impact of temperature on recruitment.