The article by Martin Daufresne, Kathrin Lengfellner, and Ulrich Sommer examines the impact of global warming on the body size of ectothermic aquatic organisms, including bacteria, phytoplankton, zooplankton, and fish. Using a meta-analysis of long-term surveys, experimental data, and published results, the authors find that global warming leads to a significant increase in the proportion of small-sized species and young age classes, while decreasing size-at-age. These findings align with ecological rules such as Bergmann’s rule, James’ rule, and the Temperature-Size Rule (TSR). The study provides evidence that reduced body size is the third universal ecological response to global warming in aquatic systems, following shifts in species ranges and seasonal changes in life cycle events. The authors discuss the implications of these findings for understanding and predicting the impacts of climate change on aquatic ecosystems.The article by Martin Daufresne, Kathrin Lengfellner, and Ulrich Sommer examines the impact of global warming on the body size of ectothermic aquatic organisms, including bacteria, phytoplankton, zooplankton, and fish. Using a meta-analysis of long-term surveys, experimental data, and published results, the authors find that global warming leads to a significant increase in the proportion of small-sized species and young age classes, while decreasing size-at-age. These findings align with ecological rules such as Bergmann’s rule, James’ rule, and the Temperature-Size Rule (TSR). The study provides evidence that reduced body size is the third universal ecological response to global warming in aquatic systems, following shifts in species ranges and seasonal changes in life cycle events. The authors discuss the implications of these findings for understanding and predicting the impacts of climate change on aquatic ecosystems.