The microbial loop plays a crucial role in Antarctic waters by helping animals survive winter, enhancing phytoplankton growth, and supporting high levels of productivity. Unlike in warmer waters, bacteria in Antarctica use old organic matter to produce food, which helps animals survive the cold season. Microbes also recycle nutrients in the water, boosting the growth of light-dependent phytoplankton. Additionally, small diatoms and phytoflagellates in Antarctica are easily eaten by animals, unlike cyanobacteria in warmer waters. These unique roles of the microbial loop explain why Antarctic waters have high levels of animal productivity despite low plant productivity.