The effect of mussel seed density on tunicate settlement and growth for the cultured mussel, Mytilus edulis

Abstract

Anecdotal reports from mussel growers suggest that increased stocking density decreases the settlement and growth of the fouling organisms Styela clava (clubbed tunicate) and Ciona intestinalis (vase tunicate). To evaluate this hypothesis, 15 mussel socks of low (90 mussels per 30 cm), medium (250 mussels per 30 cm) and high (500 mussels per 30 cm) densities were placed on three longlines in the Brudenell estuary in the fall 2005 and in the spring 2006. Sampling was conducted in June, August and October of 2006 to determine the effect of different stocking densities and socking time on mussel productivity and C. intestinalis recruitment and growth. Mussel Condition Index and shell length were not significantly different between the three stocking densities by the end of the field trial in October. In August, the mean length of C. intestinalis was significantly lower on the medium and high density socks and C. intestinalis weight was less on medium and high density socks from the fall socking period (no difference within spring socked densities), however, by the October sampling there was no biologically significant difference in the weight of C. intestinalis between stocking density treatments. Time of socking did not appear to have any significant effect on the results, although the abundance of C. intestinalis was marginally higher in August on the socks deployed in December, 2005. Mussel loss was between 50 and 60% for all treatments, with no clear pattern being evident.