Research Document - 2007/007
Quantitative Biological Risk Assessment Tool (QBRAT) v2 assessment: Codium fragile ssp. tomentosoides in the Gulf of St. Lawrence as a case study
By Drouin, A. and C.W. McKindsey
The green macroalgae Codium fragile ssp. tomentosoides (herafter, Codium) is native to Japan and has invaded water in eastern Canada. This study evaluated the risk associated with the spread of Codium fragile ssp. tomentosoides in the Gulf of St. Lawrence. Several specific objectives were thus addressed: 1) to review and synthesize the available literature on the ecology and impacts of Codium; 2) to seek the judgement of Codium experts with respect to dispersal vectors, critical habitat attributes, and probabilities and magnitudes of environmental, economic and social impacts related to the establishment of Codium by soliciting participation using a survey; 3) to evaluate the use of an Analytic Hierarchy Process (AHP) to interpret the expert judgements; 4) to do a risk assessment of Codium in the Gulf of St. Lawrence; and 5) to evaluate the utility of using the Quantitative Risk Assessment Tool (QBRAT v2) framework and software by using the Codium risk assessment as a case study.
Qualitative analysis of the literature review and the survey results suggest that Codium is quite likely to continue its expansion in the Gulf of St. Lawrence and is likely to cause damage to various components. Spread by plants or plant fragments were considered the greatest single vector for the spread of Codium. With respect to natural processes, spread by propagules was considered to be much less important. Expert judgements suggest that the most important anthropogenic vector for Codium spread is the translocation of infested objects. The presence of artificial structures and biofouling on ships were considered the next most important anthropogenic vectors whereas recreational and commercial boating and ballast water were considered to be less important. The most important criteria for habitat suitability were factors associated with substrate quality (wave exposure, area of available habitat, and substrate type) and mean water temperature. Expert judgements suggest that two of the four environmental criteria (biodiversity and trophic interactions) are considered at high risk from Codium invasion. Economic criteria were judged to be at moderate risk and social criteria at moderate or negligible risk. The AHP was quite efficient for summarizing the expert judgements and describing the error associated with the judgements for each criterion and was thus good for organizing qualitative data quantitatively. The risk assessment using the QBRAT framework showed that the Gulf of St. Lawrence is at high risk from Codium and that most of that risk was associated with further spread of the alga within the area. Future runs of QBRAT for Codium should be done for ecological, economic and social criteria separately to provide the most precise information for management purposes. The use of QBRAT v2 allowed novice users to focus their research to research to acquire all the information needed to run the risk assessment and made choices more objective. The use of the AHP combined with QBRAT v2 gave the user the ability to well define values for different criteria as well as their associated error structure. Several specific recommendations about QBRATare made.
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