Patrick T. Drake

Dispersion and connectivity estimates along the U.S. west coast from a realistic numerical model

Near-surface particle dispersion, larval dispersal and connectivity along the U.S west coast were explored using a realistic numerical model of the California Current System. Seasonal model velocities were qualitatively and quantitatively evaluated using Global Drifter Program data. The model displayed a clear seasonal cycle of eddy energy near the coast with energy maxima southwest of major headlands. Eddy speeds were correlated with drifter-based estimates during summer and fall when compared spatially. Over six million passive, Lagrangian particles were released in the upper 20 m of the water column within 10 km of the California and Oregon coasts and tracked for 7 years. The effect of subgridscale vertical turbulence was parameterized with a random walk model. Resulting trajectories yielded climatological maps of particle dispersion. Particle densities varied with release region, release season and time-since-release. Dispersal distances and coastal connectivity varied with season of release, release location, release depth and pelagic larval duration (PLD). Connectivity was clearly influenced by major geographic features such as the Gulf of the Farallones and Cape Mendocino. Given a moderate (30-60 day) PLD, mean dispersal distances varied from ~10-230 km, with standard deviations of ~130-220 km. For release locations from Palos Verdes to Point Sur, the primary direction of dispersal was northward for a moderate PLD, regardless of season. For long PLDs (120-180 day), mean dispersal distances were larger (~40-440 km), with standard deviations of ~330540 km. In winter given a long PLD, dispersal was primarily southward for release locations north of Point Arena. Increasing release depths to 40-60 m altered mean dispersal distances by 50-250 km polewards, but had little effect on standard deviations. Point Conception did not act as a barrier to dispersal for source regions in the Southern California Bight.

A Metapopulation Perspective on the Patch Dynamics of Giant Kelp in Southern California

Publisher Summary This chapter examines the patch dynamics of Macrocystis in Southern California from a metapopulation perspective and begins by synthesizing existing and new information pertaining to the metapopulation structure and dynamics of Macrocystis in the Southern California Bight. The biological and physical factors that affect colonization are reviewed, and a new empirical and theoretical estimate of spore dispersal distance for varying oceanic conditions is presented. The average kelp bed in Southern California appears to be connected to one to three neighboring kelp beds via spore dispersal for a relatively wide range of oceanographic conditions. More importantly, connectivity, even among nearby patches, seems to be mediated by spores that travel far beyond the median dispersal distance. The persistence of a giant kelp metapopulation depends on the tails of the dispersal curve and cannot be predicted simply from the average or median dispersal distance. Patch size, fecundity, and proximity to neighboring patches undoubtedly exert strong influences on the level of connectivity among patches. Compared with many terrestrial habitats, the aqueous medium through which kelp propagules disperse is relatively unstructured. Moreover, unlike passively dispersed kelp spores and drifters, immigrants in many terrestrial metapopulations exhibit complex behavioral interactions with the heterogenous landscape that influence connectivity between patches. The strong dependence of giant kelp connectivity and patch dynamics on environmental factors, such as geomorphology and oceanography, suggests that the metapopulation structure of this species is likely to differ substantially among regions.

A 4D-Var Analysis System for the California Current: A Prototype for an Operational Regional Ocean Data Assimilation System

In this chapter we will describe a comprehensive 4-dimensional variational ocean data assimilation system that is currently being used in the Regional Ocean Model System for the production of both near real-time and historical ocean analyses of the California Current circulation. The main focus of this article is on the practical aspects of the data assimilation system as applied to an energetic coastal mesoscale circulation environment.

Environmental controls on spatial patterns in the long‐term persistence of giant kelp in central California

As marine management measures increasingly protect static areas of the oceans, it is important to make sure protected areas capture and protect persistent populations. Rocky reefs in many temperate areas worldwide serve as habitat for canopy-forming macroalgae and these structure-forming species of kelps (order Laminariales) often serve as important habitat for a great diversity of species. Macrocystis pyrifera is the most common canopy-forming kelp species found along the coast of California, but the distribution and abundance of M. pyrifera varies in space and time. The purpose of this study is to determine what environmental parameters are correlated with and their relative contribution to the spatial and temporal persistence of M. pyrifera along the central coast of California and how well those environmental parameters can be used to predict areas where this species is more likely to persist. Nine environmental variables considered in this study included depth of the seafloor, structure of the rocky reef, proportion of rocky reef, size of kelp patch, biomass of kelp within a patch, distance from the edge of a kelp patch, sea surface temperature, wave orbital velocities, and population connectivity of individual kelp patches. Using a generalized linear mixed effects model (GLMM), the persistence of M. pyrifera was significantly associated with seven of the nine variables considered: depth, complexity of the rocky reef, proportion of rock, patch biomass, distance from the edge of a patch, population connectivity, and wave orbital velocities. These seven environmental variables were then used to predict the persistence of kelp across the central coast, and these predictions were compared to a reserved dataset of M. pyrifera persistence, which was not used in the creation of the GLMM. The environmental variables were shown to accurately predict the persistence of M. pyrifera within the central coast of California (r = 0.71, P < 0.001). Because persistence of giant kelp is important to the community structure of kelp forests, understanding those factors that support persistent populations of M. pyrifera will enable more effective management of these ecosystems.