In a balanced aquatic ecosystem, which group is likely to have the greatest population?

In a balanced aquatic ecosystem, plankton are likely to have the greatest population because they serve as the foundational base of the food web. Plankton, particularly phytoplankton, perform photosynthesis and produce a significant portion of the world's oxygen while also serving as the primary food source for many aquatic organisms, including small fish and various invertebrates.

Their small size and ability to reproduce rapidly enable plankton to thrive in large numbers, often reaching vast concentrations in water. This high abundance is essential for supporting higher trophic levels in the ecosystem, making them essential for maintaining the balance an ecosystem needs to thrive.

While other organisms such as fish, bacteria, and plants are also present in aquatic ecosystems, they do not typically match plankton in sheer population numbers due to the latter's critical role in nutrient cycling and energy transfer within the aquatic food web.