They live at all depths of the ocean. Most live closer to the surface due to the presence of food. Some nektons start as planktons, those that cannot swim against the moving water currents but are considered nektons once they gain swimming ability. The word ‘nekton’ is obtained from the Greek word ‘nekhein,’ meaning ‘to swim.’ The German biologist Ernst Haeckel first proposed and used the word’ nekton’ in 1891 to differentiate between the active swimmers in water bodies from the passive ones, the plankton.
Characteristics of Nektons
Types of Nektons
Chordates that include cartilaginous fishes such as sharks, several species of reptiles (turtles, snakes, and saltwater crocodiles), and mammals such as whales and sealsMollusks that include squids and octopodsArthropods, including shrimps, crabs, and lobsters
However, Nektons are more easily classified into two broader groups: vertebrates and invertebrates.
Vertebrates
Most nektons, like fish, reptiles, and mammals, fall under this group. They have bones and cartilage in their bodies.
Fish: It includes bony fishes like mackerel and tuna and cartilaginous fish like sharks. Such fishes have powerful tail fins, called caudal fins, that allow them to swim against ocean currents. Pectoral fins on their sides help them steer and maintain their orientation. Some fishes have a gas bladder that helps them to maintain buoyancy.Reptiles: These include sea turtles and sea snakes. They use their lungs for breathing air during respiration. Sea turtles use their paddle-shaped limbs, which act as fins for swimming and diving. In contrast, sea snakes have flattened tails that function as paddles.Mammals: Most mammals live exclusively in water, such as whales, dolphins, porpoises, seals, sea lions, walruses, manatees, and sea otters. However, some animals like sea lions, walruses, and sea otters also spend some time on land. They have streamlined bodies that help them swim high speed in the water.Birds: Birds such as penguins have bones with air channels. They can trap air under the feathers, which helps them in their flight.
Invertebrates
It is a relatively minor group compared to vertebrates. Invertebrates consist of:
Crustaceans: Lobsters and crabs that feed on phytoplankton and form the primary consumer level of the marine food chainMollusks: Squids and Scallops
