Modeled phytoplankton diversity and productivity in the California Current System

Abstract

We explore the phytoplankton community structure and the relationship between phytoplankton diversity and productivity produced by a self-emergent ecosystem model that represents a large number of phytoplankton type and is coupled to a circulation model of the California Current System. Biomass of each modeled phytoplankton type, when averaged over the uppermost model level and for 5-years, spans 7 orders of magnitude; 13 phytoplankton types contribute to the top 99.9% of community biomass, defining modeled species richness. Instantaneously, modeled species richness ranges between 1 and 17 while the Shannon index reaches values of 2.3. Diversity versus primary productivity shows large scatter with low species richness at both high and low productivity levels and a wide range of values including the maximum at intermediate productivities. Highest productivity and low diversity is found in the nearshore upwelling region dominated by fast growing diatoms; lowest productivity and low diversity occurs in deep, light-limited regions; and intermediate productivity and high diversity.