The Microbial Food Web and its Sensitivity to Eutrophication and Contaminant Enrichment: A Cross‐system Overview

Abstract The relative contribution to the pelagic carbon flux of bacteria, autotrophic picoplankton (APP), and heterotrophic nano‐ and microplankton is highest in pristine oligotrophic waters. Increased nutrient loading stimulates picoplankton production but reduces the importance of the microbial food web. Not all microorganisms are affected in the same way by eutrophication and contaminant enrichment. In contrast to bacteria and heterotrophic nanoflagellates, the APP was found to be highly sensitive to heavy metal contamination. The changing significance of the microbial loop has far‐reaching consequences for the entire ecosystem including alterations occurring in the benthos. The structure and functioning of the microbial food web is similar in marine, brackish, and freshwater ecosystems.