Cell growth and calcification result from uncoupled physiological processes in the soft coral Litophyton arboreum

Cellular growth and calcification were measured in branch tips of the soft coral Litophyton arboreum (Cnidaria, Octocorallia, Alcyonacea). We measured cell growth rates as 3H-thymidine incorporated into tissues, and calcification as 45Ca incorporated into sclerites, during 2 h incubations in labelled seawater. Both parameters were normalised against soft coral protein content and analysed separately as stem and polyp responses. The experiments were run at various points during coral recovery from dissection. Stems and polyps showed their lowest cell growth rate immediately after injury due to cutting (Days 1 to 3), and their highest cell growth rate during recovery time (Days 7 to 49). In all experiments, the cell growth rate of stems was significantly higher than that of polyps. By contrast, no significant difference was detected between calcification rates of stems and polyps of the fully recovered microcolonies (Days 7 to 81). This study documents for first time the independent progress of cell growth and calcification mechanisms in tropical corals. It also demonstrates the contrasting physiological potential between the body regions of soft coral colonies.