Abstract
Nonnative species pose a threat to native biodiversity and can have immense impacts on biological communities, altering the function of ecosystems. How much value is at risk from high-impact invasive species, and which parameters determine variation in that value, constitutes critical knowledge for directing both management and research, but it is rarely available. We evaluated the value of the commercial shellfish harvest that is at risk in nearshore ecosystems of Puget Sound, Washington State, USA, from the invasive European green crab, Carcinus maenas. We assessed this value using a simple static ecological model combined with an economic model using data from Puget Sound's shellfish harvest and revenue and the relationship between C. maenas abundance and the consumption rate of shellfish. The model incorporates a range in C. maenas diet preference, calories consumed per year, and crab densities. C. maenas is likely to prey on commercially harvested hardshell clams, oysters, and mussels, which would likely reduce additional revenue from processing and distribution, and the number of jobs associated with these fisheries. The model results suggest possible revenue losses of these shellfish ranging from $1.03-23.8 million USD (2.8-64% losses), with harvesting and processing losses up to $44 million USD (40%) and 303 job positions each year associated with a range of plausible parameter values. The broad range of values reflects the uncertainty in key factors underlying impacts, factors that are highly variable across invaded regions and so not knowable a priori. However, future research evaluating species invasions can reduce the uncertainty of impacts by characterizing several key parameters: density of individuals, number of arrivals, predation and competition interactions, and economic impacts. This study therefore provides direction for research to inform more accurate estimates of value-at-risk, and suggests substantial motivation for strong measures to prevent, monitor, and manage the possible invasion of C. maenas.
Highlights
In coastal ecosystems, preventing and mitigating the spread and impacts of nonnative species has become a global priority[1,2]
Commercial shellfish harvest The baseline for total shellfish harvest in Puget Sound for 2009 for hardshell clams, oysters and mussels recorded by PacFIN55 was 6.05 million kgs of shellfish, with a landed harvest value of $37.26 million USD (Table 1)
Commercial shellfish harvest at risk from green crab invasion Using the consumption model, we estimated harvested shellfish biomass and total shellfish harvest revenue associated with scenarios of low, medium and high calorie diets and densities for green crab: the medium-medium (Cal-Den) scenario yielded a value-at-risk estimate of 0.54 million kgs and $3.72 million USD in harvest revenue, a loss of 9.0%; the low-low scenario suggested a minor loss of only 0.04 million kgs and $0.08 million USD, a loss of 0.3%; and medium-high, high-medium, and high-high scenarios suggesting losses of at least 0.99 million kgs and $6.76 million USD (Table 3 and Figure 3)
Summary
In coastal ecosystems, preventing and mitigating the spread and impacts of nonnative species has become a global priority[1,2]. While many nonnative species have little to no measurable impact on their invaded regions, a few have caused great economic and ecosystem harm[3,4]. The impacts from these few invasive species can affect ecosystem function and thereby reduce the benefits that ecosystems provide for people[5,6,7,8,9]. With limited funds to manage and research coastal ecosystems, calculating the value-at-risk (the losses that might accompany the establishment of a high-impact invasive species prior to introduction) for areas not yet invaded may justify the allocation of resources to prevent, mitigate, or further understand invasive impacts[12,13]
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