While adult corals often appear fixed to the seafloor, the question of whether corals move reveals a more complex answer than a simple “no.” Many people perceive corals as entirely stationary organisms, similar to rocks or plants. However, examining their life cycle and individual components shows that corals exhibit various forms of movement. This includes dynamic stages during their early development and subtle, localized actions performed by their individual living units.
The Stationary Nature of Adult Corals
Adult stony corals are largely immobile in their mature, colony-forming stage. Once a coral larva settles onto a suitable hard surface, it undergoes metamorphosis and begins to secrete a hard calcium carbonate skeleton. This skeletal structure anchors the coral colony firmly to the seafloor. These large, established colonies remain in one location for their entire lifespan, often spanning hundreds of years.
Individual coral polyps within these colonies are encased within this rigid skeletal framework. This attachment prevents the entire colony from relocating. Their growth involves adding to this calcified structure, creating the intricate reef formations. This fixed existence defines the mature phase of most reef-building corals.
The Mobile Larval Stage
Coral movement is most evident during their larval stage. Corals reproduce by releasing free-swimming planulae into the water column. These tiny, elongated larvae possess hair-like cilia, which they rhythmically beat to propel themselves. This ciliary movement allows planulae to navigate water currents, traveling significant distances from their parent colony.
The independent movement of planula larvae is important for coral dispersal and establishing new populations. They actively seek out suitable hard substrates, such as rocks or dead coral, where they can settle. Upon finding a suitable site, a planula attaches and metamorphoses into a sessile coral polyp. This mobile phase ensures species colonization of new areas and enhances genetic diversity across coral reefs.
Subtle Movements of Coral Polyps
Even within a stationary adult coral colony, individual polyps display subtle movements. Each polyp, the coral’s living unit, can retract its soft body into its hard skeletal cup when disturbed or threatened. This shields the polyp from predators or strong water currents. Extending their tentacles is another common movement, primarily for capturing plankton and small food particles.
These tentacle extensions often occur at night, allowing the polyps to feed efficiently. Polyps can also slowly orient themselves to optimize their exposure to sunlight, which is necessary for the symbiotic algae living within their tissues. While often slow and imperceptible, these actions contribute to the polyp’s survival and the colony’s health.