Which term describes organisms that live on the water surface?

• A. Nekton
• B. Plankton
• C. Epilimnion
• D. Neuston

Answer: (D)

Understanding how aquatic organisms are categorized by where they live in relation to the air-water interface is key. Neuston refers to organisms that inhabit the very surface of the water, living in or just beneath the thin film at the air-water boundary. They’re adapted to the surface and include creatures like water striders and other surface-dwelling micro- and macro-organisms. This zone is distinct from nekton, which are animals that actively swim through the water column, and from plankton, which drift with currents within the water column rather than staying at the surface. Epilimnion is a physical term for the warm, upper layer of a stratified lake, not a biological grouping. Because neuston specifically describes surface-dwelling organisms, it is the best fit.