Nutrient supply, surface currents, and plankton dynamics predict zooplankton hotspots in coastal upwelling systems

A simple combination of wind-driven nutrient upwelling, surface currents, and plankton growth/grazing equations generates zooplankton patchiness and hotspots in coastal upwelling regions. Starting with an initial input of nitrate from coastal upwelling, growth and grazing equations evolve phytoplankton and zooplankton over time and space following surface currents. The model simulates the transition from coastal (large phytoplankton, e.g., diatoms) to offshore (picophytoplankton and microzooplankton) communities, and in between generates a large zooplankton maximum. The method was applied to four major upwelling systems (California, Peru, Northwest Africa, and Benguela) using latitudinal estimates of wind-driven nitrate supply and satellite-based surface currents. The resulting zooplankton simulations are patchy in nature; areas of high concentrations coincide with previously documented copepod and krill hotspots. The exercise highlights the importance of the upwelling process and surface currents in shaping plankton communities. Plain Language Summary Copepods and krill are important prey species for a diverse array of predators and a key link in oceanic food webs. These zooplankton concentrate in hotspots that draw fish, marine mammals, and other predators. Here we present results from a simple ecosystem model that is coupled to winds and surface currents estimated from satellite. When applied to coastal upwelling systems (California, Peru, Northwest Africa, and Benguela), the model predicts locations of zooplankton hotspots that are very similar to those identified from ship-based surveys. The results indicate that surface currents are a key driver of zooplankton spatial distribution.