Biofouling leads to reduced shell growth and flesh weight in the cultured mussel Mytilus galloprovincialis

The majority of juvenile seed mussels are lost in aquaculture production. Understanding the causes of the losses of seed mussels is critical to reducing uncertainties in mussel aquaculture production. One major cause of loss appears to be the secondary settlement behaviour of mussels, which is thought to be a behavioural process by which larger juveniles can safely recruit among adults. This implies that once a juvenile mussel has settled among adults, there is either some impetus to remain or other positive interactions that promote increased survival. In this study, 2 densities (5 and 20 per 45 cm experimental rope) of adult green-lipped mussels Perna canaliculus were deployed alongside juvenile seed mussels to test whether this enhanced the retention of the juveniles in a typical suspended culture. Adult shells were also deployed to ascertain whether any effects were due to the physical presence of the mussels or the influence of their biological functioning. The presence of adult mussels or shells did not increase the retention of juvenile P. canaliculus, but small-scale movements of juveniles were increased by the addition of 20 live adult mussels per experimental rope. However, the presence of adult mussels and mussel shells on experimental ropes greatly increased the abundance of biofouling organisms. While the addition of live adult mussels or shells failed to provide a simple tool for increasing retention of seed mussels on aquaculture lines, they offer new insights into the identity and ecology of key biofouling organisms that can be problematic in mussel aquaculture production.

Section: Discussionmentioning

confidence: 99%

Differential effects of adult mussels on the retention and fine-scale distribution of juvenile seed mussels and biofouling organisms in long-line aquaculture

South¹,

Floerl²,

Jeffs³

2017

“…On the other hand, the apparent displacement by D. vexillum appears to be less of a threat to larger mussels (> 40 mm), based on the levels of D. vexillum fouling described in our study. The impact of fouling by the solitary ascidian Ciona intestinalis on blue mussel Mytilus galloprovincialis culture in southern Australia has also been shown to be size-specific, with mussel condition significantly lower in small mussels only (Sievers et al 2013). Higher filtration rates and superior competition for resources in the larger mussels were hypothesised as the reason for the less pronounced reductions in flesh weights, and thus condition in the larger mussels (Sievers et al 2013).…”

Section: Fouling Impacts On Cultured Musselsmentioning

confidence: 99%

Impacts of the invasive ascidian Didemnum vexillum on green-lipped mussel Perna canaliculus aquaculture in New Zealand

Fletcher¹,

Forrest²,

Bell³

2013

Biofouling can pose a significant threat to shellfish aquaculture, as fouling organisms are often strong spatial competitors that are able to reach high densities or biomass in relatively short time frames. This study investigated the potential impacts of the colonial ascidian Didemnum vexillum on cultured New Zealand green-lipped mussels Perna canaliculus at one farm in the Marlborough Sounds region. Three size classes of mussels were examined: small (20 to 40 mm shell length at deployment), medium (40 to 60 mm), and large (60 to 70 mm). Replicate 4 m mussel lines were assigned to 1 of 3 treatments: (1) ambient fouling, (2) fouling enhanced by D. vexillum fragment inoculation (in addition to ambient fouling), or (3) control lines that were kept free of D. vexillum. After 15 mo, subsections of lines (0.5 m length) were processed to determine the effects of fouling cover on mussel density within lines, as well as on individual mussel size and condition. A highly significant negative relationship was shown between D. vexillum biomass and mussel density for small mussels, and to a lesser extent for medium mussels. Values of mussel condition indices were similar across size classes and across fouling treatments within each size class. These results indicate that mussels may only be vulnerable to direct D. vexillum fouling impacts at early stages of production, and that impacts may be restricted to displacement of mussels as opposed to reduced size and condition. This information will assist in the implementation of management procedures through increased understanding of D. vexillum effects at different stages of mussel production.

“…A recent review (Forrest et al 2014) found that the majority of reports of biofouling impacts on shellfish aquaculture were anecdotal, based on small-scale experimental investigations or restricted to specific locations and short time periods (e.g. Fletcher et al 2013, Sievers et al 2013.…”

Section: Introductionmentioning

confidence: 99%

Significant impact from blue mussel Mytilus galloprovincialis biofouling on aquaculture production of green-lipped mussels in New Zealand

Forrest¹,

Atalah²

2017

Biofouling by blue mussels Mytilus galloprovincialis is a persistent regional-scale problem for green-lipped mussel Perna canaliculus aquaculture in New Zealand's Marlborough Sounds. M. galloprovincialis impacts on P. canaliculus crop production were assessed using a 4 yr dataset representing 243 different mussel farms. Together with information on other production impacts from M. galloprovincialis and associated management costs, we estimated the regionalscale economic consequences of mussel biofouling. Mean (± 95% CI) M. galloprovincialis cover on mussel crops across the study region was 9.17 ± 0.5%, with the worst-affected crops experiencing up to 99% cover. P. canaliculus yield per crop depended on the spat type used for grow-out, and declined with increasing grow-out duration at a rate of ca. 1 kg yr −1 m −1 of cultivation line, due to M. galloprovincialis biofouling and a range of other possible factors. For M. galloprovincialis alone, regression models predicted a decrease in annualised P. canaliculus yield of ca. 5 to 10% at mean M. galloprovincialis cover, depending on spat type. This decline represented an average loss of regional economic value of $11.4 million yr −1 USD (range $8.0 to 15.4 million). When impacts on seed-stock supply and costs incurred for mitigation were also accounted for, the economic loss from M. galloprovincialis biofouling was estimated at $16.4 million yr −1 , which represents 10% of the regional value of the mussel industry. The discussion highlights a dearth of comparable quantitative studies of the economic consequences of biofouling. There is a need for consistent approaches to reporting such consequences to enable comparisons among different locations, biofouling species and types of aquaculture.