Response of the sea whip Halipteris willemoesi to simulated trawl disturbance and its vulnerability to subsequent predation

Abstract

Trawling Sea whip Halipteris willemoesi Seafloor habitat Nudibranch Tritonia diomedea The sea whip Halipteris willemoesi occurs in habitats coincident with bottom trawl fisheries in the Gulf of Alaska and Bering Sea and can be damaged by passing trawls. Little is known about the long-term fate of sea whips damaged by trawl gear. Sea whip responses to simulated trawl disturbance were observed in situ over a period of about 1 yr in order to assess delayed mortality from sublethal injuries. Colonies of H. willemoesi were randomly assigned to 3 treatment groups and 1 control group. Treatments were designed to mimic trawl damage including dislodgement, fracture of the axial rod, and soft tissue abrasion. Fifty percent of dislodged colonies demonstrated the ability to rebury their peduncles and recover to an erect position. Most of these colonies eventually became dislodged again without further disturbance and only one was erect at the final observation. None of the fractured colonies were able to repair their axial rods and only one was erect at the experiment's conclusion. Light tissue abrasion caused only minor tissue losses that lessened over time, and all abraded and control colonies remained erect throughout the experiment. Tissue losses among the dislodged and fractured sea whips increased throughout the experimental period and were mainly due to predation by the nudibranch Tritonia diomedea, which appeared to react with a strong scavenging response to sea whips lying on the seafloor. The presence of predators in areas where sea whips are disturbed may exacerbate trawl effects since damaged or dislodged colonies are more vulnerable to predation. © Inter-Research 2009.