Development of a method to reduce the spread of the ascidian Didemnum vexillum with aquaculture transfers

Abstract

Abstract Denny, C. M. 2008. Development of a method to reduce the spread of the ascidian Didemnum vexillum with aquaculture transfers. – ICES Journal of marine Science, 65: 805–810. The colonial ascidian Didemnum vexillum was discovered in Shakespeare Bay (New Zealand) in 2001 and now poses a serious threat to the aquaculture industry. I assess several techniques to eliminate Didemnum from Greenshell™ seed-mussels (Perna canaliculus) in order to reduce the spread of the pest species with aquaculture transfers. Simple approaches based on fresh-water immersion proved ineffective or impractical in controlling Didemnum, so different chemical treatments were evaluated. Initial trials were conducted using acetic acid at concentrations ranging from 0.1 to 10% for a range of exposure times. However, at concentrations or exposure times tolerated by seed-mussels, Didemnum colonies survived with, on average, ∼80% mortality. These results led to the testing of other chemicals, and sodium hypochlorite (bleach) was identified as a potential candidate. It was determined that dipping Didemnum in a 0.5% solution of bleach for 2 min was a 100% effective method of treatment that also left seed-mussels relatively unaffected.