What role do phytoplankton serve in aquatic ecosystems?

Phytoplankton serve a crucial role in aquatic ecosystems primarily as primary producers. By performing photosynthesis, they convert sunlight, carbon dioxide, and water into organic compounds, which in turn provide the foundational energy source for the entire food web in marine and freshwater environments. This process not only generates energy but also produces oxygen, essential for the survival of most aquatic organisms. Phytoplankton can thrive in a variety of water types, including those far from the coastline, making their presence vital to both coastal and open ocean ecosystems. Their abundance and productivity directly support higher trophic levels, such as zooplankton, fish, and other organisms that rely on them for nutrition.