Predicting the potential distribution of the vase tunicate Ciona intestinalis in Canadian waters: informing a risk assessment

Abstract

Therriault, T. W., and Herborg, L-M. 2008. Predicting the potential distribution of the vase tunicate Ciona intestinalis in Canadian waters: informing a risk assessment. – ICES Journal of Marine Science, 65: 788–794. A crucial step in characterizing the potential risk posed by non-native species is determining whether a potential invader can establish in the introduced range and what its potential distribution could be. To this end, various environmental models ranging from simple to complex have been applied to predict the potential distribution of an invader, with varying levels of success. Recently, in marine waters, tunicates have received much attention, largely because of their negative impacts on shellfish aquaculture. One of these species is the vase tunicate Ciona intestinalis, which recently has had a negative impact on aquaculture operations in Atlantic Canada and could pose a risk in Pacific Canada. To inform the risk assessment of this species, we evaluated two different types of environmental model. Simple models based on reported temperature or salinity tolerances were relatively uninformative, because almost all waters were deemed suitable. In contrast, a more complex genetic algorithm for rule-set prediction (GARP) environmental niche model, based on documented Canadian occurrence points, provided informative projections of the potential distribution in Canadian waters. In addition to informing risk assessments, these predictions can be used to focus monitoring activities, particularly towards vectors that could transport C. intestinalis to these favourable environments.