Grazing and iron limitation in the control of phytoplankton stock and nutrient concentration: a chemostat analogue of the Pacific equatorial upwelling zone

Abstract

Grazing control is essential to reproduce three conditions observed in the equatorial upwelling zone: low phytoplankton stocks, high concentrations of macronutrients, and phytoplankton specific growth rates that greatly exceed advective throughput rate in the mixed layer at the equator. Nevertheless, simultaneous grazing control and limitation by a trace nutrient such as Fe could feasibly account for observed phytoplankton specific growth rates that are less than the maximum rate possible under optimal growth conditions. Also release of an inefficiently grazed component of the phytoplankton assemblage from iron limitation seems to explain why escape from grazing control occurs under both experimental and natural Fe enrichments. -from Authors