Nekton
In ecology and paleoecology, the collective name nekton is applied to all organisms that swim actively in aquatic areas. The concept applies equally to both freshwater and oceanic systems.
The concept contrasts with other alternatives such as plankton (organisms that live in suspension and move passively), benthos (organisms that live on the bottom, whether mobile or immobile), or neuston (organisms that live at the water/water interface). air).
The numerous microscopic or near-microscopic organisms that are capable of autonomous movement, but whose displacement is determined more by the current of the water that surrounds them than by their own activity, are not considered part of the nekton, but of the plankton. To escape this dependency, an organism must be large enough (on the order of 1 cm at least) and swim actively, which is only true among animals. In the oceans, the most significant components of the nekton are fish and squid. Tetrapod vertebrates secondarily adapted to aquatic life, such as cetaceans, certain turtles or crocodiles, also fit into the concept.