Oceanographic Models and Larval Dispersal

Ocean circulation is modeled as typical July conditions with strong upwelling. Coastal Connections, vol 6

Marine ecosystems are connected and replenished by miniscule larvae borne on ocean currents. Understanding these currents is key to explaining patterns of connectivity and population replenishment in near-shore ecosystems. PISCO is currently collaborating with researchers at UCSC and UCSB to model the near-shore ocean currents that drive larval dispersal.

The PISCO modeling team (Jack Barth, Steve Gaines, Bob Warner, Margaret McManus, Libe Washburn, Chris Edwards) continues to refine nearshore ocean circulation and larval behavior models to improve understanding of the processes that cause ecological patterns in the ocean along the U.S. west coast. Connections among marine populations and habitats are influenced by the travels of young, as studied through the use of a set of coupled biological-physical models for two of PISCO's study regions (Santa Barbara Channel and Monterey Bay).

Conducting a modeling study of larval dispersal in the coastal zone requires a realistic predictive model of near-shore currents. PISCO uses a numerical model called Regional Ocean Modeling System (ROMS) for this purpose. Developed primarily at Rutgers University and UC Los Angeles (UCLA), ROMS has been widely applied in many coastal applications. PISCO employs ROMS to address important questions concerning 1) nearshore ocean dynamics and 2) larval dispersal and recruitment between relatively isolated marine populations. 

NEARSHORE Ocean Dynamics

PISCO is committed to improving ROMS capabilities on the inner shelf. The first issue is that nearshore (< 2 km) circulation patterns are complex. In the nearshore, coastal boundaries (both bathymetric and topographic) significantly alter both current and wind patterns, freshwater inputs may strengthen stratification and cause buoyancy driven flows, and tidal mixing and wave driven flows also become significant issues. Typically, oceanographic circulation models do not resolve many of these processes.

In collaboration with Chris Edwards at UCSC, PISCO is using the results of a recent hydrographic study conducted in 2007 to constrain a ROMS model and identify the processes that drive the alongshore movement of convergent fronts. Results of this effort will allow PISCO to improve understanding of nearshore ocean processes that are important to larval dispersal and recruitment.

Larval dispersal and recruitment

PISCO is developing coupled biological-physical models to evaluate connectivity and larval dispersal within the California Current Large Marine Ecosystem. Two modeling efforts are working concurrently at UCSB (Flow, Fish, and Fishing – F3 group) and UCSC (Chris Edwards). These efforts are being employed in the establishment and evaluation of Marine Protected Areas in California.

The PISCO-UCSB modeling team (with the F3 group and the ocean modeling group at UCLA) is using a data-assimilating ocean circulation model of the Southern California Bight to conduct larval dispersal studies. The circulation model is seeded using spatial production data from the PISCO surveys, model results are tested with recruitment data, and connectivity matrices are produced for recruitment periods with the goal of testing predictions about larval sources with genetics and/or microchemistry data.

The PISCO-UCSC modeling team is studying the Monterey Bay region in central California using two ocean circulation models, both of which are linked with explicit larval behavior models. Results predict higher barnacle larval settlement with wind-relaxation circulation patterns than during upwelling-favorable winds. Predicted larval settlement was similar to observed settlement patterns over an average year at two Monterey bay intertidal sites. During the upwelling season, 50% of larvae that remain within the upper 10 m are exported from the coastal environment typically within 25 days. In contrast, larvae at 40 m depth or below are retained along the central California coast for typically over 40 days. Distinct source and sink regions exist within the central California coast indicating specific population connectivity. During upwelling, larvae originating between Pt. Reyes and Pt. Arena are transported to the Gulf of the Farallones and Monterey Bay (Fig. 1). Outside the upwelling season, the Gulf of the Farallones acts as a source region for the entire central California coast.

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