The life cycle of a gorgonian: Eunicella singularis (Esper, 1794)

The life cycle of the gorgonian Eunicella singularis has been studied with emphasis on larval behaviour, metamorphosis and annual growth. Planulae are found to have a mobile phase lasting from several hours to several days. Once settled, they metamorphose into a complete primary polyp in approximately four days. In the first year, budding will yield colonies of a height between 10 and 30 mm. Subsequently, average growth rates range from 14 to 33 mm year¯¹. Death may be due to several causes. Predators may partly denude the gorgonian branches, thus facilitating the settlement of epibionts, which in turn may invade the entire skeleton, slowly pushing back the living tissue of the gorgonian. Colonies may also be torn off their substratum by wave or current action, this process sometimes being speeded up when tall epibionts such as fast growing bryozoans enhance resistance to water movement. Once toppled, the gorgonians die by necrosis of their living tissues, or by being buried under sediment. Colonies of E. singularis are estimated to reach an age of approximately 25 to 30 years. Some data have been obtained on growth rates and life spans of two other Mediterranean gorgonians, Lophogorgia ceratophyta and Paramuricea clavata.