Temporal and spatial development of an infestation of Styela clava on mussel farms in Malpeque Bay, Prince Edward Island, Canada

The first confirmed report of the invasive solitary ascidian Styela clava (clubbed tunicate) in the blue mussel (Mytilus edulis)
production area of March Water in Malpeque Bay, Prince Edward Island (PEI), occurred in September of 2002. Mussel farms in
eastern PEI waters have been challenged with heavy infestations of this tunicate since 2000, causing both production and
processing problems for the industry. A multi-year study was initiated in June of 2003 to document the spread of S. clava within
the mussel producing areas of Malpeque Bay. The study design consisted of the establishment of a series of 4 transect lines
extending outwards from the initial area of detection and the subsequent deployment of PVC collector plates at predetermined
distances. Collection plates were retrieved in late fall of each of 4 study years, and S. clava specimens were quantified for
abundance and body length. Mean recruitment levels of S. clava per collector increased from 0.4 individuals in 2003 to 370.8 in
2006. By November 2006, the geographical spread within Malpeque Bay reached approximately 12 km from the initial area of
detection. This study demonstrated that within 3 years of detection, a few individual S. clava expanded to a population at
nuisance levels for the mussel industry of PEI.