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. © 2013 Patrick T. Drake, Christopher A. Edwards, Steven G. Morgan and Edward P. Dever

Recovery trajectories of kelp forest animals are rapid yet spatially variable across a network of temperate marine protected areas

Oceans currently face a variety of threats, requiring ecosystem-based approaches to management such as networks of marine protected areas (MPAs). We evaluated changes in fish biomass on temperate rocky reefs over the decade following implementation of a network of MPAs in the northern Channel Islands, California. We found that the biomass of targeted (i.e. fished) species has increased consistently inside all MPAs in the network, with an effect of geography on the strength of the response. More interesting, biomass of targeted fish species also increased outside MPAs, although only 27% as rapidly as in the protected areas, indicating that redistribution of fishing effort has not severely affected unprotected populations. Whether the increase outside of MPAs is due to changes in fishing pressure, fisheries management actions, adult spillover, favorable environmental conditions, or a combination of all four remains unknown. We evaluated methods of controlling for biogeographic or environmental variation across networks of protected areas and found similar performance of models incorporating empirical sea surface temperature versus a simple geographic blocking term based on assemblage structure. The patterns observed are promising indicators of the success of this network, but more work is needed to understand how ecological and physical contexts affect MPA performance