Relationship between larval settlement, alongshore wind stress and surface temperature in a numerical model of the central California coastal circulation

Abstract

Author(s): Drake, PT; Edwards, CA; Morgan, SG | Abstract: Variations in larval settlement in coastal upwelling regions such as the California Current System (CCS) have been attributed to variations in physical forcing at various time and space scales, but existing findings are often conflicting and fail to explicitly consider larval transport and swimming behavior. Using virtual larvae in a realistic simulation of the CCS, temporal relationships between wind stress, temperature and nearshore settlement in central California are explored for several vertical swimming behaviors, given a pelagic larval duration (PLD) of 20 to 22 d. A robust negative correlation between upwelling-favorable, PLD-averaged wind stress and settlement was found at timescales of days to years for larvae exposed to the surface boundary layer (SBL), while settlement for larvae that remain below the layer throughout development is increased, and their overall settlement is ∼2 to 20 times higher. A 20 d running mean of the wind stress can account for 52 to 86% of logit-transformed settlement variance over the 6 yr study period. Wind stress and settlement are coherent at all intra-annual periods greater than the PLD. Monthly climatological cycles of PLD-averaged wind stress and transformed settlement are nearly identical for behaviors exposed to the SBL and constitute ∼80% of the monthly variance. Monthly anomalies of wind stress and settlement are also significantly correlated. Nearshore surface temperature is also well correlated with settlement, but significantly less so than wind stress on both seasonal and intra-seasonal timescales. Other PLDs ranging from 10 to 40 d displayed similar results. Physical forcing in this model is found to dominate intrinsic eddy variability in driving settlement.