Newsflash from the Red Sea: What does coral regeneration tell us?

Climate change and other anthropogenic stressors are leading to phase-shifts across coral reefs worldwide. In many biogeographic regions, octocorals are the most abundant alternative community, due partially to their ability to rapidly colonize vacated reef structures, providing some reef stabilization and reducing biodiversity loss. Colonization is due largely to rapid asexual reproduction and regeneration, which can even lead to invasion of alien species into new environments from a small number of founding fragments. Regeneration may act as a form of proliferation in corals, allowing dispersion and escape from mortality. Among octocorals, Xeniid species are particularly adept colonizers, with speedy asexual reproduction, year-round planulation, and few natural predators. While many aspects of xeniid physiology have been researched, their regeneration remains mostly uninvestigated, despite its potential ecological importance.

To investigate the potential of xeniids to disperse in this way, we performed a series of experiments on a local Red Sea xeniid species, Xenia umbellata. Using tissue-culture plates, we settled individual polyps in the lab and tested the limits of their regeneration. Incredibly, X. umbellata can perform structural regeneration of the oral disc within a week and whole-body regeneration from tentacles in 21 days. Most impressively, we found that this species is even capable of whole-body regeneration from polyp cuttings as small as 300 microns, with regeneration rate dependent on initial size. The ability of such fragments of differentiated coral tissue to undergo redifferentiation into a complete polyp is indicative of extremely high totipotency, and should be further investigated for its ecological significance.