What characterizes planktonic algae?

Planktonic algae are characterized by being individual cells suspended in the water column. This means that they do not attach to surfaces or form mats like some other types of algae. Instead, they float freely and are typically found in both freshwater and marine environments. Their ability to remain suspended allows them to efficiently absorb sunlight and nutrients from the water around them, which is essential for their photosynthetic processes. This freedom of movement also enables planktonic algae to play a crucial role in aquatic ecosystems, serving as a primary food source for various aquatic organisms, including zooplankton and filter-feeding fish.

The other characteristics mentioned in the other options pertain to different forms of algae, such as benthic algae, which do form mats and are often anchored to surfaces, and they can also be found in various types of water bodies, not just flowing ones.