Connectivity and larval dispersal along the Oregon coast estimated by numerical simulations

Connectivity and larval dispersal is explored off the Oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations. The study region, with strong wind-driven currents and variable topography, is modeled using the Regional Ocean Modeling System (ROMS) forced by the Coupled Ocean Atmosphere Mesoscale Prediction System. A large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 May to 28 August at depths of 1, 7, 15, 20, 50, and 75 m at every grid point shoreward of the 200 m isobath (on average 32 km offshore). The particles are transported by the three-dimensional currents of the model simulation. The competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released. Larval settlement occurs at the shallowest location during the competency time window. Connectivity matrices reveal that some of the places of highest retention are similar to the proposed Oregon marine reserve sites, especially Cape Perpetua. The Heceta Bank region has high probabilities as both a source and a destination for settled larvae. Larvae released in the Heceta Bank region often settle at higher latitudes than their release location. There are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress. Larvae are retained near the shore when the winds, averaged over the previous 6 to 8 days, are relaxed or downwelling favorable.