A management framework for preventing the secondary spread of aquatic invasive species

Biological invasions continue to accelerate, and there is a need for closer integration between invasive species research and on-the-ground management. In many regions, aquatic invasive species have established isolated populations, but have not yet spread to many sites that provide suitable habitat. In the Laurentian Great Lakes region, several Great Lakes invaders such as zebra mussel (Dreissena polymorpha), rainbow smelt (Osmerus mordax), and spiny water flea (Bythotrephes longimanus) are currently undergoing secondary spread to the smaller inland lakes and streams. This paper describes recent advances in forecasting the secondary spread of aquatic invasive species and presents a framework for assessing vulnerability of inland waters based on explicit assessment of three distinct aspects of biological invasions: colonization, site suitability, and adverse impact. In many cases, only a fraction of lakes on the landscape are vulnerable to specific invasive species, highlighting the potential application of this type of research for improving invasive species management. Effective application to on-the-ground resource management will require that research aimed at assessing site vulnerability be translated into management tools. Résumé : Les invasions biologiques continuent à augmenter en nombre, c’est pourquoi il est nécessaire de mieux intégrer la recherche sur les espèces envahissantes et leur gestion sur le terrain. Dans plusieurs régions, les espèces aquatiques envahissantes ont établi des populations isolées, mais ne se sont pas encore propagées dans plusieurs sites qui constituent des habitats appropriés. C’est le cas de la région des Grands Lacs laurentiens où des espèces qui ont envahi les Grands Lacs, telles que les moules zébrées (Dreissena polymorpha), l’éperlan arc-en-ciel (Osmerus mordax) et la puce d’eau épineuse (Bythotrephes longimanus), sont actuellement en train d’étendre secondairement leur répartition aux petits lacs et cours d’eau de l’intérieur des terres. Notre travail fait la synthèse des développements récents dans la prédiction de la dispersion secondaire des espèces aquatiques envahissantes et présente un cadre pour évaluer la vulnérabilité des eaux intérieures d’après une détermination explicite de trois aspects différents des invasions biologiques, soit la colonisation, la convenance des sites et l’impact négatif. Souvent, seule une fraction des lacs dans un paysage sont vulnérables à une espèce envahissante donnée, ce qui démontre l’intérêt potentiel de ce genre de recherche pour l’amélioration de la gestion des espèces envahissantes. Une application efficace à la gestion des ressources sur le terrain requerra cependant que la recherche sur l’évaluation de la vulnérabilité des sites soit incorporée dans des outils de gestion. [Traduit par la Rédaction] Introduction: the challenge of invasive species management In this age of globalization, human activities are rapidly dissolving the natural barriers that have historically isolated animal and plant species, providing vast opportunities for species to become biological invaders (Elton 1958). Invasive species are a leading threat to native species and biodiversity (Wilcove et al. 1998; Sala et al. 2000), are an important driver of global ecological and evolutionary change (Myers and Knoll 2001; Olden et al. 2004; Lodge et al. 2006), and have caused significant economic damage (Pimentel et al. 2005). Freshwater ecosystems are especially vulnerable to biological invasions and species extinctions because of their high degree of isolation and endemism (Richter et al. 1997; Ricciardi and Rasmussen 1999; Dudgeon et al. 2006). In response, many governments are developing management strategies for prohibiting new introductions and reducing the impacts of aquatic invasive species. The task is daunting: landscapes to be managed are vast, there are numerous invasive species, and resources available for invasive species management activities are limited. Because biological invasions are generally irreversible, invasive species prevention is the cornerstone of many manReceived 19 September 2007. Accepted 25 February 2008. Published on the NRC Research Press Web site at cjfas.nrc.ca on 25 June 2008. 20186 M.J. Vander Zanden.1 Center for Limnology, 680 N. Park St., University of Wisconsin, Madison, WI 53706, USA. J.D. Olden. School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195, USA. 1Corresponding author (e-mail: [email protected]). 1512 Can. J. Fish. Aquat. Sci. 65: 1512–1522 (2008) doi:10.1139/F08-099 # 2008 NRC Canada agement strategies (Ruesink et al. 1995; Mack et al. 2000; Simberloff 2003). The term ‘‘prevention’’ generally refers to prohibiting the entry of potentially invasive species into a country or new range, as conventional wisdom dictates that once a new invasive species establishes, it is usually impossible to eradicate or prevent its subsequent spread (Table 1). A number of national regulations and international agreements govern the movement of potentially invasive or harmful species, and protocols have been developed for assessing potential harm or invasiveness of a species being considered for import (Hayes 2003; Orr 2003; Lodge et al. 2006). More recently, quantitative approaches have been used to identify species most likely to become invasive (Ricciardi and Rasmussen 1998; Kolar and Lodge 2002; Marchetti et al. 2004). Although preventing the introduction of new invasive species is a critically important task, this approach represents only one aspect of the broader concept of invasive species prevention. Many potentially harmful invasive species have established populations outside of their native range, yet may be far from achieving their potential geographic distribution. Preventing or slowing the secondary spread of known and established invasive species to uninvaded sites is an additional aspect of invasive species prevention (Table 1) and involves a different set of goals, strategies, and target audiences than efforts to halt the import of new species (Table 1). To explore the issue of secondary spread of aquatic invasive species, we draw upon examples in the Laurentian Great Lakes region of North America. The number of nonnative species that have invaded the Great Lakes now exceeds 180, and new invaders continue to establish, primarily as the result of ballast water discharge from transoceanic vessels (Holeck et al. 2004; Ricciardi 2006). A subset of these Great Lakes invaders is spreading into the small inland lakes and streams in the surrounding region, often as unintentional hitchhikers on recreational and fishing boats. In effect, the Great Lakes are acting as stepping stones for these invasive species to reach the many thousands of ecologically diverse, smaller inland waters of North America. Inland lakes are relatively discrete ecosystems that are physically separated by land, habitat that is inhospitable to aquatic species. As a result, overland dispersal of these invasive species has been slow, and many suitable ecosystems have remained uninvaded for long periods (Johnson et al. 2006). In addition, inland lakes vary widely with regards to suitability to invasive species, a function of their individuality in physical, chemical, and biological attributes. Though the invasion of a single, small, inland lake is a relatively minor event, the potential impact of Great Lakes invasive species on small inland water bodies may be vast for several reasons. First, the Laurentian Great Lakes region contains at least several hundred thousand small lakes, along with hundreds of thousands of kilometres of rivers and streams on both sides of the Canada–US border. These inland waters provide a suite of valuable ecological services and have high recreational and ecological value (Wilson and Carpenter 1999). Many are heavily used by humans and are preferred sites for recreation and residential development (Schnaiberg et al. 2002). Current and potential economic and ecological impacts of Great Lakes invasive species on these inland water bodies are poorly characterized, though the cumulative magnitude of these impacts may be tremendous. The sheer number of inland water bodies in the Laurentian Great Lakes region, as well as many regions of the world, presents an enormous invasive species management challenge. In light of limited management resources, knowledge of which sites are vulnerable to specific invasive species is valuable because it can help direct management efforts to where they are likely to provide the greatest benefit with respect to minimizing undesired impacts of introduced species. Some of the earlier invasive species studies considered invasibility as a general attribute of a site, posing questions such as whether altered disturbance regimes and anthropogenic nutrient enrichment rendered sites more invasible (Orians 1986; Moyle and Marchetti 2006). More recent research recognizes the importance of multiple interacting factors in determining the outcome of invasions: propagule pressure, the match between site attributes and species requirements, and biotic interactions with native taxa (Kolar and Lodge 2002; Vander Zanden et al. 2004a). This paper examines the interface of research and resource management aimed at preventing or slowing the secondary spread of freshwater invasive species. There has been a great deal of progress in recent years in understanding and modeling aquatic invasive species on landscapes, specifically with regards to propagule introduction, site suitability, and impact. Each of these three factors represents a critical component of the biological invasion process, and each can contribute to assessment of site vulnerability. Identifying the specific sites on a landscape that are vulnerable to invasive species has the potential to help guide invasive species prevention programs to the locations where manageTable 1. Comparison of two invasive species prevention strategies: preventing new species from being introduced in the first place and preventing or slowing the secondary spread of invasive species that have already established regionally. Preventing introduction Preventing secondary spread Goal To keep out potentially invasive species To prevent or slow the further spread of invasive species in a region Geographic focus Borders, point-of-entry, ballast water Diffuse on landscape, invasion hubs, vulnerable sites Approach Legislative: prohibit trade and transport of potential invaders, border inspection Education and outreach to the general public Target audience Shippers, industry, importers Recreational boaters, vacationers, general public Taxonomic focus Many potential species, identity of species often unknown Small number of species, identity of species known Note: This comparison is based on the experience in the Laurentian Great Lakes, which currently support a large number of non-native species and also acts as a source habitat for the secondary spread of invasive species to smaller inland waters in the region. Vander Zanden and Olden 1513