Effects of a mucilage event on the Mediterranean gorgonianParamuricea clavata. I ‐ Short term impacts at the population and colony levels

A Paramuricea clavata population thriving between 29 and 39 m depth on a shoal at the northern entrance to the Strait of Messina (Tyrrhenian Sea) was affected by mucilage coverage at the end of summer 1993. Mucilage became entangled in projecting branches and necrotized the coenenchyme below, leaving the axial skeleton bare. The entire population was heavily affected, extent of injuries being negatively correlated with size of colonies. Colony size, scale and location of damage were related to successful regeneration after six months. Smaller colonies showed a higher mortality, while colonies with over 50–60% of their total branch length damaged were overgrown by invaders and died. The extent of injuries in the central part of the colony was found to be a critical parameter in determining colony regrowth. A number of injured colonies grew during the six months following the disappearance of mucilage, which shows that their regrowth was apparently not influenced by stress due to mucilage.