A physically coupled end-to-end model platform for coastal ecosystems: Simulating the effects of climate change and changing upwelling characteristics on the Northern California Current ecosystem

We describe a spatially explicit, intermediate complexity end-to-end model platform that integrates physical, trophic, and nutrient cycling processes. A two-dimensional advection and mixing model drives nitrate input into the model continental shelf domain, the transport of nutrients and plankton between sub-regions, and the export of nutrients and plankton from the model domain. Trophic relationships are defined by classical mass-balanced food web model techniques (e.g., ECOPATH). Inclusion of nitrate and ammonium nutrient pools and bacterial recycling of detritus allows consideration of alternate “new” vs. “recycled” production regimes. The model platform was applied to the Northern California Current (NCC) shelf ecosystem. Seasonal upwelling of nutrients along the coast is the primary driver of NCC productivity, however the characteristics of upwelling vary considerably between years and are expected to change into the future as a result of global climate change. The model was run under alternate physical driver scenarios to examine the effects of changing upwelling characteristics on the production and spatial distribution of functional groups across all trophic levels. Productivity on the shelf had a dome-shaped relationship with upwelling strength. As the intensity of individual upwelling events increased, productivity increased throughout the food web. However, strong upwelling had a detrimental effect when the physical export of plankton exceeded the capacity of phytoplankton to exploit higher nutrient supply rates and the capacity of zooplankton to exploit higher phytoplankton production. As the duration of individual upwelling events increased (an implication of some climate change scenarios) model simulations predicted an overall reduction of productivity at all trophic levels and a shift in the size composition of the phytoplankton community, especially within the nearshore region.