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

摘要

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~(TM) 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.