Simulation and field measurements of phytoplankton-bacteria- zooplankton interactions in the southern Benguela upwelling region

Abstract

A general size-based model is used to predict the complex temporal successions observed in planktonic communities after an upwelling event in the southern Benguela, and to resolve a number of fundamental questions regarding the trophic dynamics of the pelagic food web. The model predicts rapid growth of a phytoplankton community dominated by nanophytoplankton-sized cells and a later net phytoplankton bloom. After nitrate depletion the bloom is dominated by nanophytoplankton dependent upon regenerated nitrogen. Analysis of C and N flows showed that respiration and grazing were largely responsible for the decline of the phytoplankton bloom, accounting for 47 and 44% respectively of the total C fixed by phytoplankton over the 20 d period. Mesozooplankton grazed 62% of the declining bloom (Days 10 to 20), but only 18% of the total C fixed. The microbial food web played an important role in N cycling and in the production of mesozooplankton throughout the simulation period. -from Authors