The metabolic theory of ecology and algal bloom formation

Rose and Caron (2007) have compiled a comprehensive data set of individual growth rates of planktonic protists in an attempt to answer a fundamental question in marine ecology: ‘‘Why are blooms of phytoplankton such common events in the ocean?’’. They reach the interesting conclusion that, because the temperature dependence of the growth rate of heterotrophic protists is much stronger than that of autotrophic protists, the growth rates of algal grazers will be much lower than that of their prey when water temperatures are low. They conclude that this reduced predator growth will result in a lower grazing pressure, allowing frequent algal blooms to develop in polar regions. Most importantly, they speculate that this difference in the temperature dependence of heterotrophic and autotrophic growth might be due to their differing metabolic pathways. Here I try to link their results to the metabolic theory of ecology (MTE) (Brown et al. 2004), and I argue that the conclusion of Rose and Caron (2007) is very similar to one of the predictions of MTE. MTE predicts a different temperature dependence for heterotrophic processes (mostly driven by adenosine triphosphate synthesis) and autotrophic rates (controlled by Rubisco carboxylation) (Allen et al. 2005). To describe the effects of temperature on metabolic processes, MTE uses the Van’t Hoff–Arrhenius equation (Arrhenius 1915), closely related to Boltzmann’s factor (Gillooly et al. 2001, 2002; Brown et al. 2004; Allen et al. 2005):