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

Garth Arsenault

doi:10.3391/ai.2009.4.1.19

Abstract

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.

Highlights

In September 2002, mussel producers in the March Water area of Malpeque Bay, Prince Edward Island (PEI) reported a low abundance of the clubbed tunicate (Styela clava Herdman 1882) on their mussel crop
Recruitment occurs in PEI waters from late June to late October, with maximum recruitment occurring in late September (Bourque et al 2007)
Fewer than 15 individual S. clava specimens were detected during the SCUBA diving survey of all mussel leases in October 2002

Summary

Introduction

In September 2002, mussel producers in the March Water area of Malpeque Bay, Prince Edward Island (PEI) reported a low abundance of the clubbed tunicate (Styela clava Herdman 1882) on their mussel crop. Present in several other mussel production areas of PEI since 1998, this exotic tunicate had not previously been detected in March Water. This ascidian species was initially identified on a mussel farm in the Brudenell River in January 1998 and by 2001 had spread to several additional areas in the southeastern waters of PEI (Thompson and MacNair 2004). Each new detection of S. clava in mussel producing estuaries of eastern PEI rapidly developed into a substantial infestation within 2 to 3 years, resulting in increased costs associated with growing, harvesting and processing the mussel crop (Thompson and MacNair 2004; Canada DFO 2006)

Methods

Results

Conclusion