The Life Cycle of a Gorgonian: Eunicella Singularis (Esper, 1794)

Abstract

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.

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“…Such negative growth rates have been observed in other tropical (Yoshioka and Yoshioka 1991;Lasker et al 2003) or temperate gorgonian species (Weinberg and Weinberg 1979;Matsumoto 2003). For instance, Coma et al (1998) showed that in P. clavata, 23% of the branches exhibited a null growth rate and 12.4% exhibited a decrease in primary branch length.…”

“…Local studies of the congeneric species E. singularis also indicated a lifespan of 25-30 years (Weinberg and Weinberg 1979) whereas other gorgonians, for instance P. clavata, may grow over 60 years (Linares et al 2007). Within the population studied, colony disappearance is high for colonies in size classes over 370 cm 2 (with an estimated age of over 30 years old).…”

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“…High growth rates in injured colonies were also observed in other gorgonian species (Weinberg & Weinberg, 1979;Castanaro & Lasker, 2003;Sanchez & Lasker, 2004). It has been reported that octocoral colony size (Grigg, 1972;Velimirov, 1976) and growth rates (Velimirov, 1975;Sebens, 1984;Kim & Lasker, 1997) are affected by water flow.…”

“…In addition, heterogeneity of growth rate within a community was observed. Previous investigators reported that the growth rate varied both within a colony (Velimirov, 1975;Weinberg & Weinberg, 1979;Brazeau & Lasker, 1992;Castanaro & Lasker, 2003) and within a species (Birkeland, 1974;Velimirov, 1975;Weinberg & Weinberg, 1979;Yoshioka & Yoshioka, 1991;Weinbauer & Velimirov, 1995). Factors that influence variation in seasonal growth include water temperature (Grigg, 1974;Velimirov, 1975;Coma et al, 1998a), food abundance, and seasonal reproduction (Grigg, 1974).…”

“…Although the fan shape of many species appears to have symmetrical branching, the iterative growth of these branches is not continuous and homogeneous. It has been reported that each branch grows independently (Velimirov, 1975;Weinberg & Weinberg, 1979;Brazeau & Lasker, 1992;Castanaro & Lasker, 2003).…”