Free swimming macroscopic animals in an aquatic environment are referred to as

In aquatic ecosystems, organisms are categorized based on their mobility and habitat. Nekton refers to the group of relatively large and powerful animals that are active swimmers, capable of overcoming water currents and navigating independently [2]. This group includes macroscopic animals such as fish, squids, and marine mammals like whales [2]. In contrast, plankton are microscopic or small organisms whose distribution is largely controlled by water currents due to limited locomotory power [4]. Benthos consists of organisms living on or in the bottom sediments of the water mass, such as corals and sea urchins. Periphyton refers to organisms, typically algae, attached to submerged surfaces like stems of rooted plants. Therefore, free-swimming macroscopic animals that can move independently of the ambient flow are classified as nekton.

Sources

1. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Classifcation of marine ecosystems > p. 31
2. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > iv) Nekton: > p. 33
3. [4] https://www.sciencedirect.com/topics/immunology-and-microbiology/plankton