Indicator #07
Invasive species (human-induced)
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Dennis Lassuy, North Slope Science Initiative, U.S. Dept. of the Interior Anchorage, Alaska, USA.
Patrick N. Lewis, WWF International Arctic Programme, Oslo, Norway.

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As humans and their goods and services have become increasingly mobile, so too have the intended and unintended movements of species. In many cases, the intended benefits of species movement (food, fiber, recreation) have been realized. In other cases, both unintentional and intentional introductions have had harmful results [1]. The term “invasive species” is used here to reflect this latter situation and refers to species that are not native to a given ecosystem (i.e., when a species is present due to an intentional or unintentional escape, release, dissemination, or placement into that ecosystem as a result of human activity) and which may cause economic or environmental harm (including harm to subsistence species and activities) or which may cause harm to human health. It should be noted that some nonnative species considered to pose no invasive threat may exhibit explosive population growth long after their initial establishment in a new environment [2], leading to invasive impacts, despite initially being considered benign.

Biological invasion is now widely recognized as second only to habitat alteration as a factor in the endangerment and extinction of native species [3, 4], and is arguably the less reversible of the two. Indeed, many consider invasive species, together with climate change, to be among the most important ecological challenges facing global ecosystems today. The impacts of invasive species are not limited to ecological harm. The annual economic impact of invasive species has been estimated at between $13 and $34 billion CAD for a subset of invasive species

in Canada [5] and considerably more in the United States where estimates of economic impacts are in excess of $138 billion USD per year [6].

Impacts on cultural systems are harder to define, but two things are clear: 1) as native biodiversity is lost, so too are the potential human uses of that biodiversity, and 2) climate change will increase the likelihood of biological invasions in the Arctic. The combination of these two factors, plus the existence of many vibrant subsistence cultures in the Arctic which rely on native flora and fauna, suggest this is a timely opportunity for additional study.

Population/ecosystem status and trends

Biological invasions are known from around the globe but are relatively less known or studied in the Arctic. In their analysis of coastal marine invasions, de Rivera et al. [7] noted a pattern of decreasing diversity and abundance of non-native species with increasing latitude. This does not mean the Arctic is not susceptible. In fact, a subsequent study estimated that a suite of marine invasive species, including the European green crab, Carcinus maenas, had the potential to expand to sub-Arctic and Arctic waters even under moderate climate change scenarios [8]. Similarly, Ruiz and Hewitt [9] concluded that “environmental changes may greatly increase invasion opportunity at high northern latitudes due to shipping, mineral exploration, shoreline development, and other human responses.”

This secondary migration of invasives complicates ecological interactions as naturally occurring species from areas adjacent to the Arctic are also expanding their ranges northward [10]. Another study found that the rate of marine invasion is increasing; that most reported invasions are by crustaceans and molluscs; and, importantly, that most invasions have resulted from shipping [11]. Given the findings of the recent analysis of current Arctic shipping (Figure 7.1) and the potential for climate change to expand such shipping [12], this has potentially very high relevance for future marine invasive risks to Arctic waters. In fact, in August 2009, two German vessels moving Korean goods from Vladivostok to the Netherlands along the Northern Sea Route became the first legal commercial ship crossings of the Arctic without icebreaker assistance [13]. Studies of polar shipping operations have demonstrated that the external hull and ballast tanks of vessels operating in ice-covered waters can support a wide variety of nonnative marine organisms [14, 15].

To date, there are many fewer invasive terrestrial plants known from the Arctic than in the more highly altered and invaded ecosystems of lower latitudes. However, even Arctic ecosystems are susceptible to invasion. Over a dozen invasive plant species are already known from the ecozones of the Canadian Arctic and many more have reached ecozones to their immediate south [16]. In the Alaskan Arctic, 39 taxa of introduced plants (or roughly 7% of the total Arctic flora) have been reported, including a suite of highly invasive grasses and clovers [17]. Another highly invasive plant, white sweet clover, Melilotus alba, has now spread up the Dalton Highway to above the Arctic Circle in Alaska. This nitrogen fixing invader has the potential to alter soil chemistry, with unknown consequences for native plant species that have evolved in low nitrogen systems. Invasive plants are even known in the high Arctic, with 15% of the flora from a survey in Svalbard reported to be non-native species [18].

Concerns for the future

2As climate change alters Arctic ecosystems and enables greater human activity, biological invasions are likely to increase in the Arctic. To some extent, Arctic terrestrial ecosystems may be predisposed to invasion because many invasive plants are adapted to open disturbed areas. If fire frequency and intensity increase with climate change, this may further enhance invasion susceptibility. Sites of human disturbance and those located along pathways of human activity (e.g., shipping, including port facilities, and road corridors) are the most likely focal points of invasion into Arctic habitats. One study, for example, noted the susceptibility of gravel-rich river corridors to invasion by Melilotus, a type of clover, from bridge crossings [19].

The ability for climate change to directly enhance invasion has been demonstrated for marine tunicates [20] and the spread of invasive marine tunicates to the Arctic could present a significant risk to benthic-feeding marine mammals that are already at risk (e.g., several whale and pinniped species). Benthic communities in northern Norway and the Kola Peninsula in Russia are already facing significant disturbance from the introduced red king crab, Paralithodes camtschaticus [21], and further introductions may contribute to accelerated and synergistic impacts (e.g. [22]). Range map scenarios developed for 16 highly invasive plants either occurring in or at risk of invading Alaska [23] also paint a sobering

outlook for the future. Figure 7.2 depicts the potential expansion of one invasive aquatic plant, Hydrilla veticillata, well up into Arctic Alaska ecosystems and even into far eastern Russian aquatic systems. Another recent study examining global distribution trends associated with climate change predicted that marine communities in the Arctic and Antarctic will be the most at risk from climate induced invasions [10].

Because future change will be best understood when measured against a credible baseline, much more work similar to that of Ruiz et al. [24] will be needed. Due to the distribution of resources in the Arctic, the development of cost-effective early detection monitoring networks will be a challenge. Special attention should be given to monitoring around key points of introduction via the unloading of goods, such as ports and airports, or in areas likely to see increased ship deballasting or at higher risk of shipwrecks. Engaging a network of citizen scientists might present a viable alternative to traditional monitoring approaches. Such networks could represent an excellent opportunity to employ the traditional ecological knowledge of northern residents. After all, who knows better when something “different” appears in an ecosystem than those who have used the native species of that ecosystem for millennia?

In addition to valid baselines, there will need to be increased and targeted prevention efforts to limit the influx on non-native species (e.g., ballast water treatment, inspection and treatment of containers and packaging material, and the effective cleaning and treatment of ship hulls and drilling rigs brought in from other marine ecosystems). Such measures should be complemented with targeted management plans for activities known to present a high risk of introduction. For example, petroleum drilling rigs have been identified as a significant risk for modern marine introductions, and the increase of petroleum extraction in the Arctic should be accompanied by stringent cleaning and monitoring requirements [25].

3Finally, two additional future Arctic risks that may accompany climate change: 1) much like climate change, invasive species can decrease stability and increase uncertainty in ecosystem function and the evolutionary trajectories of its component species; and 2) as more southern ecosystems feel the effects of these climateinduced uncertainties, there may be a push to resort to using Arctic ecosystems as refugia at the receiving end of well-intended but risky efforts to “assist” species in the colonization of new habitats [26]. Since ability of species to successfully invade will vary with their mobility and physiological capacities, much work is also needed on basic biology and life history traits of potential Arctic invaders in order to effectively assess Arctic vulnerabilities and risks.