Monitoring for invasive tunicates in Nova Scotia, Canada (2006-2009)

Dawn Sephton,Joanne Keays,Benedikte Vercaemer,Jean Marc Nicolas

doi:10.3391/ai.2011.6.4.04

Abstract

The shellfish culture industry in Atlantic Canada has been adversely affected by the presence of non-indigenous, invasive tunicates since the mid-1990’s. A Fisheries and Oceans Canada Aquatic Invasive Species (DFO-AIS) monitoring program documented the presence, establishment, and spread of five tunicate species at geo-referenced coastal monitoring stations in Nova Scotian waters from 2006-2009. Styela clava (Herdman, 1881) and Didemnum vexillum (Kott, 2002) were not found in Nova Scotia during the course of this study, despite their problematic presence in Prince Edward Island and the Gulf of Maine, respectively. Botryllus schlosseri (Pallas, 1766) was the most widely distributed species, found at more than 69% of sites monitored in all years. Ciona intestinalis (Linnaeus, 1767) was present at about half of the stations in all years, and while its populations were heaviest and most persistent in the Halifax – St. Margaret’s Bay, Shelburne – Port La Tour, and Canso – Isle Madame areas, there was evidence of spread on the eastern and Fundy shores, and in Cape Breton. Botrylloides violaceus (Oka, 1927), was the least common tunicate encountered, but its distribution increased from 19% of stations in 2006 to 50% of stations in 2009. Tunicates occupied a wide variety of hard substrates (natural and artificial) in waters with 13.0 to 33.2 salinity and at oxygen saturations of 32.5 to 124.8%.

Highlights

Non-indigenous ascidians, or tunicates, have become a concern to global marine ecosystems in recent years due to their adverse effects on native species (Lambert 2001; Lutz-Collins et al 2009) and communities (Blum et al 2007; Dijkstra et al 2007)
The pattern of occurrence of tunicates was similar in all years (Table 1); B. schlosseri was the dominant species of tunicate reported (69 – 84% of records), followed by C. intestinalis
The distribution of B. violaceus increased from 19% of stations in 2006 to 50% of stations in 2009

Summary

Introduction

Non-indigenous ascidians, or tunicates, have become a concern to global marine ecosystems in recent years due to their adverse effects on native species (Lambert 2001; Lutz-Collins et al 2009) and communities (Blum et al 2007; Dijkstra et al 2007). The golden star tunicate Botryllus schlosseri (Pallas, 1766), present since 2001, and the violet tunicate Botrylloides violaceus (Oka, 1927) present since 2002 (Locke et al 2009), have spread to many areas These colonial species are regarded as the least problematic of the PEI tunicate invaders (Locke et al 2009), because S. clava and C. intestinalis are more aggressive competitors (Carver et al 2006a; Clarke and Therriault 2007) and are the dominant tunicate foulers in terms of biomass on mussel farms (Thompson and MacNair 2004; Lutz-Collins et al 2009)

Methods

Results

Conclusion