ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 16, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(5):795-804; doi:10.1093/icesjms/fsn083
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Organism impact assessment: risk analysis for post-incursion management
National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, Locked Bag 1370, Newnham, Tasmania 7250, Australia
tel: +61 3 6324 3813; fax: +61 3 6324 3840; e-mail: m.campbell{at}amc.edu.au
Campbell, M. L. 2008. Organism impact assessment: risk analysis for post-incursion management. – ICES Journal of Marine Science, 65: 795–804.Risk analysis is a management tool that is becoming increasingly common in biosecurity because it aids decision-making in the face of uncertainty. A risk analysis model [referred to as an organism impact assessment (OIA)] is described, one that was developed in New Zealand to facilitate the management of incursions of introduced aquatic species in a post-border (after quarantine is breached) scenario. The New Zealand biosecurity risk-management framework assesses ecological, cultural, social, and economic values congruently, ensuring that a transparent and objective framework is established with clearly stated ecological and socio-political imperatives. Using expert heuristics and published and observed data, the present study assesses the likelihood that a target introduced species will have ecological, cultural, social, and economic impacts. The consequences (impact and/or change) of such events are then determined, to establish a relative risk ranking, using consequence matrices to aid assessment of the ecological, cultural, social, and economic value impacts of species unintentionally introduced to New Zealand. To illustrate the risk model, the OIA for the incursion of the fresh-water diatom Didymosphenia geminata is presented. The likelihood and consequences resulting in risk pertaining to the introduction of D. geminata varied across regions, but based on public perception at the initial incursion location, Southland, D. geminata was considered to be an extreme risk across all core values.
Keywords: biosecurity, Didymosphenia geminata, introduced species, New Zealand, risk assessment
Received 21 June 2007; accepted 7 April 2008; advance access publication 16 May 2008.
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Introduction |
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 Top Introduction New Zealand core valuesThe New Zealand D....The OIA (risk analysis)...DiscussionConclusionsReferences |
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Introduced species pose a significant threat to native biodiversity, economic well-being, the sense of connectedness to the marine ecosystem, and the spirituality of many individual countries. As such, the management of these threats has high priority at international, national, and regional levels. Management of intentionally imported introduced species is typically controlled with the aid of Import Health Standards in a pre-border and border management context. Import Health Standards operate as codified rule structures that identify how, when, and where a specific "risk trade-good" can be imported and adhere to the related standards of the World Trade Organization (WTO). Yet, many species are imported unintentionally (Carlton, 2001; Hewitt et al., 2004a, b), so evading pre-border and border management attempts. In such cases, post-border management is implemented, with the application of surveillance and incursion management. When a new species is first identified, its status (introduced, cryptogenic, or native) is assessed rapidly (through methods such as the ten-point criteria of Chapman and Carlton, 1991, 1994). Consequently, if the new species is considered to have been introduced, then eradication may be attempted or control measures implemented. A decision to eradicate or control is often based on limited data, requiring the use of risk analysis to aid decision-making in the face of such uncertainty.
Risk analysis is used to determine the frequency of an event (incursion or spread) and the level of consequence (impact) for that event. Within Australia and New Zealand, risk management (analysis and assessment) follows standards for best practice (Standards Australia, 2000, 2004). The risk management standard is summarized in four steps: (i) establishing the context (hazard identification); (ii) identifying the risk (hazard analysis); (iii) assessing the risks (risk analysis and risk evaluation); (iv) treating the risks (management action, including eradication and control). In the context of New Zealand biosecurity, the third step of this process is concerned with determining likelihood and consequences and calculating risk, which is assessed using an organism impact assessment (OIA).
An OIA determines the likelihood of an introduced species spreading and the level of impact that such an event would have on predetermined core values (environmental, economic, social, and cultural issues). OIAs are useful when evaluating new species that have limited distributions and for high-impact and/or high-profile species.
Here, I use the example of the fresh-water diatom Didymosphenia geminata incursion within New Zealand to illustrate how an OIA can be used within a post-border incursion response situation. The objective of an OIA is to provide salient, credible, and legitimate information to decision-makers, when data are limited and uncertain. A full account of this analysis is available at www.biosecurity.govt.nz/files/pests-diseases/plants/didymo/didymo-org-impact-assessment.pdf.
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New Zealand core values |
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Within New Zealand, environment, economic, cultural, and social values are considered important, with biosecurity assessed against each. The values can be summarized as:
- Environment—from the biological to the physical characteristics of an ecosystem being assessed, excluding extractive use and aesthetic value.
- Economic—components within an ecosystem that provide a current or potential economic gain or loss.
- Social—the values placed on a location in relation to human use for pleasure, aesthetic, and generational values.
- Cultural—aspects of the aquatic environment that represent an iconic or spiritual value, including those that create a sense of local, regional, or national identity.
Each core value consists of a number of subcomponents that are broad-ranging and elicit different perceptions between stakeholders. Subcomponents also vary spatially (from region to region) and temporally (over time). Because of this variation, it is important to update risk analyses regularly.
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The New Zealand D. geminata incursion |
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Didymosphenia geminata is a fresh-water diatom that was detected in southern waterways of the New Zealand’s South Island in 2004. It is native to the Ponto–Caspian bioregion (Kawecka and Sanecki, 2003) and has been introduced to parts of Eurasia and the UK (Foged, 1978; Antoine and Benson-Evans, 1986; Krammer and Lange-Bertalot, 1997; Wen and Zhi-hui, 1999; Jonsson et al., 2000; Kara and Sahin, 2001; Kawecka and Sanecki, 2003; Subakov-Simic and Cvijan, 2004; Acs et al., 2005), North America (Patrick and Reimer, 1975; Sheath et al., 1986; Cardinale et al., 2006; Shea et al., 2007; Porter et al., in press), and New Zealand (one prior record, which is thought to be erroneous; C. Viegleis, pers. comm.).
The organism has a broad range of ecological tolerances: detected in water temperatures ranging from 0.1°C (cool alpine; Patrick and Reimer, 1975; Krammer and Lange-Bertalot, 1997) to 22°C (warm lowland; Kawecka and Sanecki, 2003; Kilroy, 2004), with a preference for high concentrations of nutrients, shade, hard substrata, and depth (Wilcox et al., 1994; Subakov-Simic and Cvijan, 2004), but it is also found in soft, sandy sediments (Sutherland et al., 2005) and in shallow water (Sherbot and Bothwell, 1993). The species reproduces sexually and asexually (Round et al., 1990) and forms large, dense mats of mucilaginous (siliceous) material (Kilroy, 2004).
Reported impacts of D. geminata are mostly based on subjective observations, rather than empirical studies, of impact, with a resulting varied opinion of the extent of impact (Jonsson et al., 2000; Kawecka and Sanecki, 2003; Sutherland et al., 2005). Some examples of subjective assessments of impact include the reduction of dissolved oxygen in the water column, abrasion of fish gills and skin, elimination of competing macrophytes, and irritation of human skin (Jonsson et al., 2000; Spaulding et al., 2005).
Following the detection of D. geminata in New Zealand, several research projects were funded by Biosecurity New Zealand to elucidate the species’ autoecology further and to support the risk analysis embedded within the OIA. These supporting projects had three aims: (i) to examine the realized vs. the fundamental niche of D. geminata in New Zealand waterways, and hence to provide information on the likelihood of spread (Kilroy et al., 2005); (ii) to determine the perceived value of New Zealand rivers (Atkinson and Rapley, 2005); and (iii) to assess the perceived impact on New Zealand rivers after a D. geminata incursion (Atkinson and Rapley, 2005).
Using information from the commissioned projects and the literature (published and grey), an OIA risk analysis was undertaken. The OIA follows six steps:
- identifying core-value subcomponents;
- quantifying the value of the subcomponents identified;
- determining the likelihood of a D. geminata incursion in different regions;
- determining the consequences of a D. geminata incursion (i.e. the extent of the impact D. geminata could have on each subcomponent);
- determining risk;
- assessing uncertainty.
As little empirical evidence of impact by D. geminata exists in the published literature, a Delphic approach (measured perceptions) was adopted. It used focus groups from three regions: the bottom of the South Island (Southland, where the incursion was first identified), the top of the South Island, and Hawkes Bay (North Island). Focus group participants consisted of Maori (indigenous people), scientific experts, government officials, environmental and conservation groups, industry (tourism, aquaculture, and fishing), local constituents, stakeholders, and other interested parties, ensuring representation from a broad range of societal perceptions.
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The OIA (risk analysis) process |
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TopIntroductionNew Zealand core valuesThe New Zealand D....The OIA (risk analysis)...DiscussionConclusionsReferences |
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Step 1: identifying core-value subcomponents
Stakeholders and experts involved in the perceived impacts study (Atkinson and Rapley, 2005) identified a set of subcomponents to each core value, which was added to those collected from the literature to produce a generic table of subcomponents for New Zealand waterways (see Campbell, 2005). In all, 73 core-value subcomponents were identified, 16 environmental, 17 economic, 31 social, and 9 cultural values (Table 1).
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Step 2: quantifying the value of the subcomponents identified
The first objective of the focus group participants was to assess the perceived value of New Zealand river systems (Table 2). Using contingent valuation, a NZ dollar value associated with each core value was then assigned (Atkinson and Rapley, 2005). Cultural values were assessed against a value continuum that had a scale of 0–100 (0 being the lowest and 100 the highest values). This valuation method addressed both use (direct use, indirect use, and option value) and non-use values (existence value). Here, we use an economics-based definition for option value (i.e. preserving the option to use in the future ecosystem goods and services that may not be used at present; Pagiola et al., 2004) and existence value (i.e. enjoyment people may experience simply from knowing that a resource exists, even if they never expect to use that resource themselves; Pagiola et al., 2004).
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Values were assessed using contingent and, where possible, market valuation (see Atkinson and Rapley, 2005). Contingent valuation works by asking focus group participants to state their beliefs about the value of a specified service, or their willingness to pay to preserve this specified service. It is applicable to all ecosystem services and benefits, but typically is used for non-use values (Gilpin, 2000; Chee, 2004; Pagiola et al., 2004).
Step 3: determining the likelihood of a D. geminata incursion in different regions
Predicted incursions into various New Zealand regions were determined by delineating habitats that D. geminata could inhabit, based on environmental characteristics of the known current distribution of D. geminata in its newly invaded region (a New Zealand realized niche) and the known environmental requirements of the species, based on global knowledge (globally realized niche). Thus, the predicted New Zealand range of D. geminata is based on environmental and physiological matching. After the potential incursion range had been determined, the ranges were assessed against a standardized likelihood matrix (Table 3).
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The outcome of the predictive analyses using the New Zealand realized niche data indicated that of 29 river systems, D. geminata was likely to establish in three (10%). When considering the globally realized niche data, the result was more precautionary, with D. geminata possibly establishing in 26 (90%) of 29 river systems. In this analysis, no ranges are provided because the uncertainty is constrained to the most conservative value within each region.
Step 4: determining the consequences (the extent of the impact that D. geminata could have on each identified subcomponent)
The consequences (or likely impact) D. geminata will have on New Zealand core values were explored by examining the belief systems of (i.e. extracting heuristic knowledge) focus group participants. Consequence was derived by determining the perceived change in value of a river after D. geminata arrived. Perceived change in value was measured by subtracting the perceived value of the region after D. geminata arrived from the perceived value of a region before it arrived (Table 2). The perceived change is then measured against the consequence matrices to derive a measure of consequence (Campbell, 2005; Table 4). It is imperative that consequence matrices capture the intensity or extent of the impact, and the geographical extent and permanence or duration of the impact.
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The environment is a dynamic and robust system, with many alterations in species, habitats, and geomorphology being indistinguishable from natural background variation. The consequence matrices attempt to reflect this robustness by using threshold levels, represented by percentage values. Minor shifts in economic growth can cause the collapse of business and trade, so threshold values for the economic consequence matrix are low, to represent this sensitivity (E. Gonzalez, pers. comm.). Social and cultural change is difficult to quantify and will vary greatly from region to region and person to person. Typically, humans are unwilling to accept large social change because it is often deemed to affect individuals directly (E. Gonzalez, pers. comm.). Also, significant uncertainty exists around cultural perceptions, but this uncertainty can be reduced if the correct focus group participants are targeted (e.g. including indigenous peoples). Threshold values were developed through national and international workshops, international literature, and with aid from ecologists, invasion biologists, and economists. The values are readily adaptable and can be altered to meet spatial or temporal needs across a range of circumstances.
The OIA consequence analysis assumes that if D. geminata is established in a river system, the likelihood of impact can be deemed certain (a probability of 1). The outcomes of the analysis indicate that the environment was perceived as the most impacted core value (average 62% change ± 29% s.d.), with the consequence of this ranging from major (at the top of the South Island and in Hawkes Bay) to significant (in Southland; Table 5). The perceived economic impact revealed a 53 ± 23% s.d. change, with a perceived significant consequence (Table 5). Perceived social impact revealed a 37 ± 30% s.d. change, with perceived consequence ranging from moderate (at the top of the South Island) to significant (in Hawkes Bay; Table 5). Perceived cultural impacts revealed a 36 ± 31% s.d. change, with a perceived consequence range of major (in Southland and Hawkes Bay) to significant (at the top of the South Island).
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Step 5: determining risk
Estimated risk was assessed for each core value against a standard risk matrix (Table 6), with the outcomes summarized for each of the focus group regions in Table 5. Ranges of estimated risk for a core value represent the uncertainty between regions. The following trends were apparent. Perceived risk to environmental core values varied from high at the top of the South Island and in Hawkes Bay to extreme in Southland, where the incursion of the species was first seen (Table 5). However, based on a limited risk analysis (only assessed on one environmental subcomponent) undertaken by Kilroy et al. (2005), risk was considered negligible. Therefore, perceived environmental risk varied from negligible to extreme. Perceived economic risk was extreme, with limited to no uncertainty in perceptions between regions (Table 5). Perceived social risk contained uncertainty between regions, with a variation of estimated risk from high (at the top of the South Island) to extreme (in Southland and Hawkes Bay; Table 5). Similarly, cultural risk also contained uncertainty between regions, with Hawkes Bay estimated to have a high risk and both Southland and the top of the South Island estimated to have extreme risk.
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Step 6: assessing uncertainty
Regardless of the method used, evaluations will have uncertainty surrounding their outcomes. This can be the result of either measurement error or real variability in the assessment. Delphic evaluations attempt to differentiate these sources of uncertainty by increasing the sample size from which opinions are derived (the number of experts), identifying to the best of the assessor’s ability the appropriate experts, and by using multiple questions to examine consistency in opinions. The Delphic evaluations assessed here evaluated opinions across 160 participants (Atkinson and Rapley, 2005). Different participants will have different levels of understanding, knowledge, and perceptions, so how they value a core value and how they assess impact will vary. To capture this, the range consequences perceived by focus group participants were averaged, and the variability across regions was used to represent uncertainty. A narrow range of views illustrates less uncertainty, whereas a greater range represents more uncertainty.
When attempting to predict impact, as risk analysis in a marine biosecurity context does, the analyses are often considered objective, being based on quantitative data. However, in some instances, quantitative data are not available or conflicting, so the information itself has uncertainty (variability) associated with it. Evaluating impacts attempt to determine the importance of these impacts, primarily a subjective issue. This is particularly the case in a management context, where other imperatives (political, social, cultural, economic, and environmental) may influence the decision-making process. The subjective nature of risk (particularly when based on limited datasets) results in uncertainty that can be clarified by using scenario-testing, undertaking sensitivity analyses, using worst-case scenarios based on precautionary principles, demonstrating points of view, and monitoring uncertainty. In this risk assessment, the uncertainty is presented as the range of perceptions identified by the expert community. By representing the full range of perceptions, the uncertainty is clearly presented for consideration in the political process that determines how management will attempt to manage the incursion of D. geminata in different regions.
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Discussion |
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TopIntroductionNew Zealand core valuesThe New Zealand D....The OIA (risk analysis)...DiscussionConclusionsReferences |
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An OIA is an essential risk-assessment tool that aids decision-makers faced with biosecurity breaches across a country’s border. In a post-border situation, the detection and early response to an unintentional incursion is paramount to ensuring successful eradication or control (Figure 1; Williamson, 1996; Hewitt and Campbell, 2007). When the data pertaining to a species impact are readily available (e.g. for Sargassum muticum), the risk-assessment process is straightforward, with likelihood, consequence, and subsequent risk being readily determined by following standard risk procedures. However, in situations where impact data are limited or conflicting, the risk assessment becomes more complex (NRC, 1996; but see the discussion in Hayes and Hewitt, 2001). In such situations, the use of a Delphic process may provide a means of completing data gaps, making the risk assessment tractable.
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In the current instance, the incursion of D. geminata into the Southland region of New Zealand was assessed to determine the overall risk to both local (Southland) and wider New Zealand values. Risk consists of the likelihood or probability that an event will occur, multiplied by the consequence or severity of that event. In many risk evaluations of introduced species, likelihood is determined through a variety of processes, including calculating the probability of association between the species of concern and transport vectors (Hayes and Hewitt, 2001; Andow, 2003; Hayes and Sliwa, 2003; Hewitt et al., 2004a), the probability of survival of the species during transport (Hayes and Hewitt, 2001), the frequency of the transport vector as a surrogate for propagule pressure (Drake and Lodge, 2004), and the likelihood of survival in the new region (Hayes and Hewitt, 2001; Kilroy et al., 2005; Barry et al., 2008). In this evaluation, the likelihood was based on a comparison of the global and New Zealand realized niches to determine the percentage of river sections in which D. geminata could survive. Based on this outcome, the likelihood of a successful incursion into these regions was deemed highly likely, given that all regions had a high percentage of river sections that met the niche requirements of D. geminata, and spread within New Zealand was deemed impossible to prevent, because of a lack of internal borders (Hewitt et al., 2004b; Branson, 2006).
Consequence, on the other hand, is the probability of the extent of impact and is generally assessed for a single value (economic impact, Pimentel et al., 2000, 2001; biodiversity impact, Orr et al., 1993). Here, assessment across all four core values is required under New Zealand Biosecurity legislation, with the ability to provide equal weighting for advice to government. The consequence matrices (Table 4) have been adapted to incorporate consistency in the level of impact, using similar wording and metrics across the four values.
The outcomes of this risk assessment provided transparent and rapid advice that could be used by managers to respond successfully to the urgent need of decision-makers. Within the Southland region, perception of the risk posed by the incursion of D. geminata was extreme across all values. This is not surprising, given that Southland is where the D. geminata incursion was first recorded and, at the time of the original risk assessment, D. geminata had not been detected in any other waterway.
Both the top of the South Island and Hawkes Bay also perceived D. geminata as a threat, with tested incursion scenarios resulting in high-to-extreme risk perceptions across the core values. Again, this perception of risk from an introduced species context is not surprising, given that New Zealanders perceive their environment as unique and a source of national identity. They largely perceive themselves as being "green" or ecologically sensitive, and introduced species in any ecosystem are widely considered to undermine natural biodiversity. New Zealanders are also made aware of introduced species across all ecosystems, through aggressive education programmes. They have been exposed to a number of well-advertised pests (e.g. painted apple moth); multiple government agencies work closely in conjunction to manage biosecurity; and there exists a comprehensive and proactive National Biosecurity Strategy (Biosecurity Strategy, 2003).
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Conclusions |
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Based on the outcomes of this OIA and further economic analyses undertaken by Biosecurity New Zealand (Branson, 2006), an eradication attempt was rejected by management. Instead, an aggressive public awareness programme was established, and restrictions on movement into and out of infected areas were implemented. However, since 2005, D. geminata has been found throughout all major river systems in the South Island of New Zealand, and it is expected to be found soon in the North Island. Therefore, its subsequent detection in many river systems supports the conservative outcomes of this OIA, which should be advocated in future management decisions.
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Acknowledgements |
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I acknowledge and thank the funding agency Biosecurity New Zealand, in particular Christine Reed and Christina Viegleis for arranging and providing support, and Exequiel Gonzalez, Garth Atkinson, and Bruce Rapley for their insights on economic analyses. Finally, I thank the reviewers for their insightful comments, which strengthened the paper.
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References |
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