The use of food grade oil in the prevention of vase tunicate fouling on mussel aquaculture gear

The blue mussel (Mytilus edulis L. 1758) aquaculture industry plays an important role in Prince Edward Island (PEI)’s economy, annually producing around 17.5 Mt of product and generating $48.7 million in revenue (DFO 2006). Over the past decade, the productivity of the industry has been challenged by the rising costs associated with biofouling of aquaculture gear. Central to the problem are four recently arrived species of invasive tunicates (class Ascidiacea): Styela clava Herdman 1881, Botryllus schlosseri Pallas 1766, Botrylloides violaceus Oka 1927 and Ciona intestinalis L. 1758. Their establishment in PEI estuaries was facilitated by the high nutrient load and the large amount of suspended artificial substrates in the form of aquaculture gear in these systems (Locke et al. 2007). The number of invasive tunicates species in PEI waters will likely increase in the future; at least two other species have recently been found in nearby waters: Didemnum vexillum Kott, 2005 in Eastport, Maine, US (Jennifer Dijkstra, Wells National Abstract

In 2008, algal wet weight was significantly reduced on treated buoys and spat collectors but not on treated mussel socks when compared to controls (Table 1).
Compared to controls, an 87% reduction in wet weights of other tunicates was observed on treated buoys, but not on the other substrates (Table 1).In   2).

Discussion and Conclusions
Efficacy of shortening at reducing C.

Figure 1 .
Figure 1.The solitary tunicate Ciona intestinalis with body parts indicated (A) and growing in large clusters in the field (B).
was selected based on its relatively high melting point of 45-50 °C (ADM Packaged Oils 2010).Since temperatures of PEI estuarine waters have been recorded only as high as 23 °C, the shortening was expected to remain solid in the water throughout the summer season.All trials were conducted using artificial salt water at 26-27 ppt (Instant Ocean®).

Figure 2 .FieldFigure 3
Figure 2. Experimental setup on a mussel longline in St. Mary's Bay, PEI.Mussel socks, buoys, spat collectors, and PVC collector plates were either dipped in shortening (treated) or left untreated (control).Replicates from each substrate were arranged alternating treated and untreated (indicated by different shading).Only one replicate per substrate and treatment is shown in this figure.

Figure 4
Figure 4 (right).Representative experimental spat collector ropes (A) four days following deployment in July 2008 and (B) immediately prior to retrieval in August 2008.Spat collector ropes were either dipped in melted shortening (Trt) before deployment or left untreated (Con).

Figure 5 .
Figure 5. Experimental collector plates immediately (A) prior to and (B) after retrieval in August 2008, following a four-week deployment in St. Mary's Bay, PEI.Collector plates were either dipped in melted shortening (Trt) before deployment or left untreated (Con) .

Figure 6 .
Figure 6.Experimental buoys immediately (A) prior to and (B) after retrieval in August 2008, following a four-week deployment in St. Mary's Bay, PEI.Buoys were either left untreated (control) or dipped in melted shortening (treatment) before deployment.

Figure 7 .
Figure 7. Effect of shortening treatment on C. intestinalis wet weight on four substrates.Mussel sock data and spat collector data are standardized to 1 m.Differences between shortening-treated and control groups for each substrate were detected using Student's t test.* indicates p < 0.05, ** indicates p < 0.001.SD = standard deviation.

Figure 8 .
Figure 8.Effect of shortening treatment on C. intestinalis abundance on four substrates.Mussel sock data and spat collector data are standardized to 1 m.Differences between shortening-treated and control groups for each substrate were detected using Student's t test.* indicates p < 0.05, ** indicates p < 0.001.SD = standard deviation.

Figure 9 .
Figure 9.Effect of shortening treatment on C. intestinalis length on four substrates.Differences between shortening-treated and control groups for each substrate were detected using two way ANOVA for spat collectors and Student's t test for all other substrates.* indicates p < 0.05, ** indicates p < 0.001.SD = standard deviation, N/A = data not available.
the oil on boats.The cost of shortening application was CAN$0.10 per buoy, CAN$0.06 per metre of spat collector rope, CAN$1.29 per metre of mussel sock and CAN$0.04 per three collector

Table 2 .
Effect of shortening treatment on mussel biomass, density and length on two substrate types.Mussel sock sections and spat collectors were either dipped in shortening or left untreated (control).Substrates were deployed on a mussel lease for 4 weeks in 2008 and for 17 weeks in 2009.Significance determined with Student's t test.N/A: not available because of little to no spat settlement on the lines in 2008; ns = not significant.for