Effects of mechanical experimental disturbance on aspects of colony responses, reproduction and regeneration in the cold water octocoral Gersemia rubiformis

Responses of delicate soft corals to mechanical injuries inflicted by bottom fishing (e.g., trawling, dredging) are not known. Effects of mechanical disturbance on the soft coral Gersemia rubiformis (Ehrenberg, 1834) were examined by experimentally simulating disturbances caused by bottom fishing. Eight colonies were collected in the Bay of Fundy and maintained in individual aquaria. Four colonies were rolled over and crushed 10 times, once every 2 weeks over 2 months, while four were left undisturbed. Colony response was recorded both 4 days and 1 week post disturbance in both treatments by assigning states reflecting colony and polyp physiognomy. Proportions of corals in different states did not differ between treatments over time. Crushing immediately induced complete colony retraction and daughter colonies were produced in crushed corals. Randomly amplified polymorphic DNA genetic markers demonstrated that daughter colonies were sexually derived. Despite initial fast growth, daughter colonies experienced high mortality. Premature larval expulsion may have been intrinsically initiated to dispose of resource-costly planulae during colony repair. Corals regenerated well from acute localized injuries, which, along with the ability to temporarily retract and survive repeated crushing, may benefit G. rubiformis in heavily disturbed habitats such as areas impacted by bottom fishing activities where the probability of mechanical disturbance is high.