What role do phytoplankton play in aquatic systems?

Phytoplankton are crucial components of aquatic ecosystems as they serve as primary producers, which means they are the foundation of the food web in these environments. Through the process of photosynthesis, they convert sunlight, carbon dioxide, and nutrients into organic matter, which supports a diverse range of marine and freshwater life, including zooplankton, fish, and various invertebrates. Because they are the primary source of energy for these organisms, any changes in phytoplankton populations can significantly impact the entire ecosystem.

In contrasting roles, decomposers break down organic matter and recycle nutrients, top predators are apex species that regulate populations of their prey, and pollutants are substances that harm aquatic systems. Phytoplankton do not fit these definitions, emphasizing their unique and essential role as the primary producers in aquatic environments.