Evaluation of In Situ Phytoplankton Growth Rates: A Synthesis of Data from Varied Approaches

The use of clean sampling and incubation methods and the development of biomass-independent techniques for estimating the rates of growth and grazing mortality of phytoplankton in the ocean have resulted in estimates of phytoplankton growth rates that are approximately twice those reported prior to roughly 1980. Light-saturated growth rates in tropical and subtropical latitudes correspond to a doubling time of roughly 1 day. The results of mesoscale nutrient-enrichment experiments and comparison of growth rates with estimates of strictly temperature-limited rates indicate that light-saturated growth rates are no more than 50% of nutrient-saturated values, a conclusion consistent with the resiliency of food webs to perturbations. Phytoplankton growth rates in the euphotic zone of the ocean appear to be controlled largely by the grazing activities of micro- and mesozooplankton and the recycling of nutrients associated with the catabolism of consumed prey.