A screening procedure for potential tunicate invaders of Atlantic Canada

Andrea Locke

doi:10.3391/ai.2009.4.1.7

Abstract

The conditions for a successful invasion involve the intersection of a species, its vector, and an appropriate receiving environment. Species distribution (biogeography) and availability of a shipping vector were used as filters to reduce a list of 57 tunicates with a history of invasion in marine or estuarine waters worldwide, to a more manageable basis for a “watch list” or “trigger list” for non-indigenous invasive tunicates in Atlantic Canada. Seven species from the worldwide invasives list were already present in Atlantic Canada: the non-indigenous Styela clava, Ciona intestinalis (cryptogenic in southern Nova Scotia but non-indigenous in northern Atlantic Canada), Botryllus schlosseri, Botrylloides violaceus and Molgula manhattensis, and the native Aplidium glabrum and Didemnum candidum. Nine species, not currently present in Atlantic Canada, were removed from the analysis due to insufficient distribution data. All of the remaining 41 species co-occurred in one or more bioregions with species presently found in Atlantic Canada. Examination of distributions relative to shipping patterns eliminated eight species not present in the areas with the most shipping traffic to Atlantic Canada: the eastern seaboard of the USA, the Caribbean Sea, northern Europe and the Mediterranean Sea. A climate zone filter to remove species found only in subtropical or tropical waters eliminated 21 species. Applying both the shipping and climate zone filters resulted in a “watch list” of 17 tunicate species considered the most likely to successfully invade Atlantic Canada: Ascidia sydneiensis, Ascidiella aspersa, Botrylloides leachi, Clavelina lepadiformis, Cnemidocarpa irene, Corella eumyota, Cystodytes dellechiajei, Didemnum vexillum, Diplosoma listerianum, Perophora japonica, Perophora multiclathrata, Phallusia mammillata, Polyandrocarpa zorritensis, Polyclinum constellatum, Styela canopus, Styela plicata, and Symplegma brakenhielmi.

Highlights

Prediction of species invasions that are likely to occur in a particular bioregion or ecosystem is considered a prerequisite for developing a “watch list” for early detection or “trigger list” for rapid response (Ricciardi and Rasmussen 1998; Locke and Hanson 2009)
The starting point for this analysis was a list of 57 tunicate species with a history of invasion somewhere in the world; distribution records were supplemented for the 40 species listed in the database of Hayes et al (2004) and records of another 17 species were obtained from a survey of the scientific literature and invasive species websites (Table 1)
Of the 57 tunicate species with a history of invasion somewhere in the world, seven already occur in Atlantic Canada and there were insufficient data to analyze the distributions of nine species

Summary

Introduction

Prediction of species invasions that are likely to occur in a particular bioregion or ecosystem is considered a prerequisite for developing a “watch list” for early detection (to determine where and how to monitor species of concern) or “trigger list” for rapid response (to identify what risk assessments and control methods should be prepared ahead of time) (Ricciardi and Rasmussen 1998; Locke and Hanson 2009). There have been numerous attempts to model and predict species invasions (e.g.,Williamson and Fitter 1996; Ricciardi and Rasmussen 1998; Smith et al 1999; Kolar and Lodge 2001; Peterson and Vieglais 2001; Peterson 2003; Reusser and Lee 2005; Nyberg and Wallentinus 2005; Miller et al 2007). The effort required to obtain this detailed information may be justified in the study of a few high-risk species, but there is a need for a rapid screening tool that can narrow down a list of potential invaders from an extensive list of candidates (e.g., Ricciardi and Rasmussen 1998)

Methods

Results

Conclusion