The term “nektonic” describes the vast assemblage of aquatic animals that actively swim and navigate through the water, independent of currents. Proposed by German biologist Ernst Haeckel in 1891, the word originates from the Greek “nekhein,” meaning “to swim.” This classification separates powerful swimmers from other marine life based on their method of locomotion. These organisms possess the ability to purposefully move from one place to another, a capacity that defines their ecological function. Their movement is not passive; it is self-propelled, allowing them to hunt, migrate, and evade threats across great distances.
Defining Characteristics of Nekton
The unifying trait of all nektonic animals is their ability to generate thrust to overcome the resistance of water and move against its flow. This is accomplished through physical adaptations for propulsion. Many fish, for instance, have streamlined, torpedo-shaped bodies that minimize drag, coupled with caudal (tail) fins that beat side-to-side to create forward motion. Pectoral fins on their sides act like rudders, providing steering and stability.
Other nektonic creatures have evolved different solutions for movement. Cephalopods such as squid utilize a form of jet propulsion, forcefully expelling water from a muscular cavity to shoot through their environment. Marine mammals like whales and dolphins use powerful, vertically oriented tail flukes to propel their large bodies. Nearly all nektonic organisms are macroscopic, meaning they are large enough to be seen with the naked eye.
Nekton vs. Other Marine Lifestyles
The independence of movement that defines nekton becomes clearer when contrasted with other marine life strategies. One such group is plankton, which encompasses a huge diversity of organisms that drift with the currents. While some planktonic creatures can perform small vertical migrations, they are ultimately unable to swim against the prevailing water movement. Many animals begin life as planktonic larvae and only become nektonic once they grow large and strong enough to swim on their own.
Another distinct category is the benthos, which comprises organisms living on, in, or attached to the seafloor. This group includes animals like crabs, sea stars, and corals that crawl, burrow, or remain fixed in one place. Unlike the free-swimming nekton that occupies the water column, benthic life is fundamentally tied to the substrate at the bottom of the ocean.
Examples of Nektonic Animals
The nekton category is incredibly diverse, spanning multiple phyla and including some of the ocean’s most recognizable animals.
- Fish are among the most abundant, with both bony fish like tuna and mackerel and cartilaginous fish like sharks serving as prime examples built for speed and endurance.
- Marine mammals are another prominent group, including air-breathing animals like whales, dolphins, seals, and porpoises that are powerful swimmers.
- In the mollusk phylum, the most notable nektonic members are cephalopods, with squid and octopuses using specialized jet propulsion to move swiftly.
- Even some reptiles are classified as nektonic, such as sea turtles and sea snakes, which have adapted to a life of active swimming in the marine world.
Habitat and Distribution of Nekton
Nektonic animals primarily inhabit the pelagic zone, the vast expanse of open water away from the coast and seafloor. Their distribution is not uniform and is often limited by physical and biological factors like water temperature, salinity, and the availability of food.
Different species are adapted to live at specific depths within the water column. Some, like the whale shark, are often found near the sunlit surface, or epipelagic zone, feeding on plankton. Other species are adapted to the pressure and darkness of the deep sea. Many species undertake extensive vertical and horizontal migrations for feeding or reproduction.