Clonal propagation by the azooxanthellate octocoral Dendronephthya hemprichi

Abstract.

 The azooxanthellate octocoral Dendronephthya hemprichi (Octocorallia, Alcyonacea) is the most abundant benthic organism inhabiting the under-water surfaces of oil jetties at Eilat (Red Sea); however, it is very rare on Eilat’s natural reefs. This soft coral exhibits a newly discovered mode of clonal propagation that results in autotomy of small-sized fragments (2–5 mm in length). They possess specialized root-like processes that enable a rapid attachment onto the substrata. An autotomy event is completed within only 2 days; large colonies can bear hundreds of pre-detached fragments. Temporal fluctuations in the percentage of fragment-bearing colonies indicate that autotomy is stimulated by exogenous factors, probably flow-related events. Recruitment of fragments onto PVC plates placed horizontally adjacent to D. hemprichi colonies, was immediate and remarkably high. Attached fragments were observed 2 days after placement of plates; after 52 days, densities of more than one recruit per cm² were recorded. The negative buoyancy of fragments causes them to land on horizontal surfaces rather than on vertical ones. However, their survivorship on vertical surfaces is much higher. This pattern corresponds with dominance of D. hemprichi on vertical substrata at the oil jetties and on natural vertical reefs of the northern Red Sea. Such a mode of clonal propagation provides an efficient mean for genets of D. hemprichi to exploit food resources within a zooxanthellate-dominated reef community.