What characterizes the primary production in deeper aquatic areas?

The primary production in deeper aquatic areas is primarily driven by phytoplankton. In these environments, light penetration is limited, which restricts the growth of larger plant species that require more sunlight, such as macrophytes. Phytoplankton, which are microscopic algae, thrive in these conditions due to their ability to quickly utilize available nutrients and reproduce rapidly. They are typically suspended in the water column and can photosynthesize in the upper layers where light reaches, contributing significantly to the overall biomass and productivity of aquatic ecosystems.

In contrast, the other factors mentioned do not characterize primary production in these deeper areas effectively. Larger plant species are less prevalent in deeper waters, shredders—organisms that break down leaf litter and detritus—are more significant in terrestrial or shallow water environments, and surface runoff more directly influences littoral zones rather than the deeper aquatic areas, as it primarily affects nutrient inputs near the surface rather than the photic depth where phytoplankton dominate production. This underscores the critical role phytoplankton play in fueling the aquatic food web and their importance in nutrient cycling within these ecosystems.