The effect of anti-fouling treatments for the clubbed tunicate on the blue mussel, Mytilus edulis

Abstract

A major problem for the mussel aquaculture industry on Prince Edward Island, Canada surfaced in the late 1990s with the introduction of a fouling organism commonly known as the clubbed tunicate, Styela clava. This organism has the ability to infest mussel cultivation equipment to the point where productivity is severely compromised. This study examined the effects two anti-fouling treatments, air exposure and acetic acid, had on experimental mussel populations. Socked mussel seed obtained from a mussel farm on Prince Edward Island was exposed to three treatment regimes and subsequently placed on a long-line in New London Bay, P.E.I. The treatments were a 40-h air exposure, 30-s 5% acetic acid immersion and a 2-min 5% acetic acid immersion. Treatment effects on mussels were measured after seven months in the field, along with untreated controls. Mussel quality was assessed using mussel sock weights, length, condition index and changes in genetic characteristics measured at allozyme loci. A significant decrease in mean sock weights was found for all three treatments compared to control sock weights ( p < 0.05). Sock weights for the air exposure, 30-s acetic acid dip and 2-min acetic acid dip were reduced by 38%, 67%, and 74% respectively compared to control sock weights. This revealed a significant loss in productivity (incl. mortality and loss of attachment) in the treated mussel populations. However, results on the other characteristics used to assess mussel fitness found no long-term effects on the health or genetic structure of the mussel populations that survived the treatment regimes. Although air exposure is now considered an inefficient method to kill post-larval Styela clava, the results provide preliminary evidence regarding the safe use of the acetic acid treatment regimes tested in terms of long-term mussel population health.