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

We evaluate the impact of changing ocean conditions on larval recruitment of purple sea urchins in the Southern California Bight using 3D biophysical modeling with temperature, surface chlorophyll, and recruitment data. The influence of circulation, temperature, and food supply on larval recruitment is quantified using modeled variables, which include larval dispersal distance, larval source location, larval food supply, and temperature exposure for larvae and adults and 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 or 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, but temperature exposure for larvae during the spring recruitment season is not. Thus, we hypothesize that the timing of species recruitment and reproduction is a critical factor in predicting the impact of temperature on 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. Food supply is not found to be a driver of larval recruitment.