An emergent community ecosystem model applied to the California Current System

An ecosystem model that supports considerable phytoplankton diversity is coupled to a circulation model of the California Current System. The Regional Ocean Modeling System is configured for a realistic simulation at 0.1° resolution for years 2000–2004. The concentration-based ecosystem model includes multiple nutrients, dissolved and particulate organic pools, two grazers, and 78 phytoplankton organism. Primary producers divide into 4 functional groups representing diatoms, large phytoplankton that do not require silicate, Prochlorococcus-like organisms, and small phytoplankton that can use nitrate. Random selection of phytoplankton growth parameters creates an autotrophic community able to fill multiple environmental niches created by the physical circulation and plankton population. In the 5-year average, over 98% of the total biomass at the surface is contained within 8 primary producers, with 30 additional phytoplankton sustained at lower levels. Modeled surface phytoplankton biomass is evaluated on multi-annual and seasonal bases using satellite chlorophyll estimates for the same period. The self-organized communities produced by the model represent various features of the California Current Ecosystem, including the biogeographic break at Pt. Conception. The annual average fields generally reveal high diatom concentrations nearshore, with small phytoplankton more broadly distributed. Prochlorococcus-like organisms are absent or at relatively low concentrations at the coast, increasing across the California Current. Small non-Prochlorococcus-like phytoplankton types are found at highest concentrations nearshore and far offshore. The model exhibits both surface and subsurface features, including a seasonal subsurface chlorophyll maximum along CalCOFI Line 77 between May and October. Time-series of area averaged model fields show seasonal progressions of different phytoplankton groups.