MEPS 585:99-112 (2017)  -  DOI: https://doi.org/10.3354/meps12437

ABSTRACT: Spread of a non-indigenous ascidian (NIA), Botryllus schlosseri (Tunicata: Ascidiacea), has been detected since 2006 in coastal waters of Newfoundland. This species has been of economic concern because NIA can be a costly nuisance for bivalve aquaculture. The presence of this temperate-adapted species in Newfoundland represents an extension of its global range into subarctic waters. In 2010 and 2011, we investigated the population dynamics of B. schlosseri in Arnold’s Cove, Placentia Bay, Newfoundland and Labrador, Canada. Experiments testing the influence of season, depth, and substrate type on larval recruitment rates were conducted within the harbour over a period of 20 mo. Seasonal cycle of colony (adult) abundance was determined from video surveys of a belt transect of the wharf. The seasonal window of recruitment was from August to mid-October (ca. 2.5 mo), constrained to temperatures ≥13°C. Peak recruitment was observed coincident with maximum seasonal temperature in September. Recruitment was greatest at 1 m depth on PVC plates. Colonies were present year-round on wharf structures and exhibited seasonal fluctuations in percent cover, from <1% in May to ca. 3% in October. Seasonal increase in colony abundance was constrained to temperatures >5°C. These findings provide a population-level understanding of how a temperate-adapted, non-indigenous species is established and maintained in a subarctic environment. Our results suggest that 1 sampling site may adequately represent the spatial scale of ≤10s of metres within a marina, and NIA monitoring could target specific seasons, depths, and substrate types for optimal species detection.

KEY WORDS: Botryllus schlosseri · Tunicate · Phenology · Depth-dependent recruitment · Substrate type · Aquatic invasive species · Newfoundland