Influence of larval behavior on transport and population connectivity in a realistic simulation of the California Current System

Using an implementation of the Region Ocean Modeling System, we investigate the influence of larval vertical swimming on spring dispersal for nearshore invertebrate species in the California Current System (CCS), with a focus on central California and the Bodega Bay area. Larvae are given a suite of idealized behaviors designed to reveal the importance of the surface boundary layer (SBL) to transport and settlement. Larvae remain near 5 m, 30 m, or transition between these depths using various strategies, including diel vertical migration (DVM) and ontogenetic vertical migration. Some behaviors result in modeled densities qualitatively similar to observed cross-shelf larval distributions. By remaining primarily below the SBL, larvae released from central California are 500 times more likely to be retained within 5 km of the coast at 30 days from release relative to those that stay near surface, and 145 times more likely to settle along the coast within a 30 to 60 day pelagic larval duration. For most behaviors, nearshore retention over time could be approximated as a modified exponential decay process. Vertical swimming also greatly affects alongshore dispersal, with each behavior resulting in a unique structure of alongshore settlement. Maintaining a depth near 30 m increases settlement throughout most of the CCS by at least an order of magnitude relative to passive larvae. Remaining near surface reduces settlement from Pt. Conception to Pt. Arena, but has less of an effect north of Cape Mendocino. Relative to passive larvae, DVM increases settlement in regional "hotspots," but does not greatly alter overall recruitment in the CCS, and ontogenetic vertical migration increases settlement for central California regions south of Bodega Bay.