Spatial and temporal patterns of recruitment of the tunicate Ciona intestinalis on a mussel farm in Nova Scotia, Canada

Although possibly indigenous to Nova Scotia, the ascidian Ciona intestinalis has become a problem for local mussel aquaculturists. The local population ecology of the ascidian was studied by recording the depth, distribution, and timing of recruitment of C. intestinalis at four different locations (high wave exposure, low wave exposure, recently fallowed, and historically heavily fouled with tunicates) on a mussel farm at Indian Point, Nova Scotia. Animals were collected weekly from 11 collectors deployed at a depth of 4.5 m over two seasons (June-December 2003 and 2004). Recruitment occurred in two peaks during both seasons: the first peak lasted from late June to late July while the second peak lasted from early September to mid-November. Recruitment was highest in the sheltered and historically fouled location, intermediate in the fallowed site, and lowest in the site with highest wave exposure. Collectors were also deployed at different depths. Recruitment was highest at 4.5 m and to a lesser extent at 8.5 m. Little recruitment was seen at the surface (0.5 m) or in deeper water (12.5 and 16.5 m), except during the second peak in 2004. Overall, these results seem to indicate an abbreviated larval dispersal phase with young recruits settling very close to the pool of adults located on the mussel lines.