Eukaryotic microalgae, like diatoms and dinoflagellates, are important in marine ecosystems. Scientists studied the isotopic fingerprints of these microalgae to see how they contribute to food webs. They found distinct fingerprints for different groups of microalgae, which can help identify their role in the food chain. Surprisingly, temperature didn't affect these fingerprints much. By using these fingerprints, scientists could trace the sources of organic matter in marine systems, like penguins eating diatoms or corals getting food from dinoflagellates. This research helps us understand how different microalgae impact the carbon cycle in the ocean.