Human-mediated dispersal of aquatic nonindigenous species: impacts and interventions

The introduction and establishment of species beyond the boundaries of their native ranges is an environmental issue of increasing scope and seriousness. This dissertation examines the consequences of the establishment of aquatic nonindigenous species (NIS) in the Laurentian Great Lakes (GL) region and also investigates alternatives for reducing anthropogenic spread of nuisance aquatic NIS.

I first investigate the pathways by which aquatic NIS are introduced to the GL to learn if introduction pathway is related to where species originate and how likely they are to have spread beyond the GL basin. My analysis shows that ballast water release is highly likely to introduce new aquatic NIS to North America, whereas unauthorized release of organisms in trade tends to introduce to the GL aquatic NIS already established in North America. Moreover, it appears that it is primarily a matter of time before novel NIS that become established in the GL appear in other North American waterways. I also consider the relationship between introduction pathway and species impacts, finding that there is an apparent relationship, but that further study of species-specific impacts is needed to verify this finding.

Given the importance of ballast water release in bringing novel species to the GL, I use a novel technique to estimate the economic impacts in the region of ecological changes caused by populations of aquatic NIS introduced by this pathway. This study concludes that the economic impacts of ballast water species are large, but are also uncertain. Nevertheless, policies that aim to reduce the likelihood of additional invasions via this pathway appear to be economically justifiable.

As nuisance aquatic NIS in the GL region spread to other waterways, they bring with them ecological and economic impacts. The detrimental nature of these impacts motivates efforts to reduce the rate of spread. To inform such efforts, I test the efficacy of multiple methods for removing aquatic NIS from recreational boats and trailers. I found that visual inspection and hand removal is highly effective in removing the nuisance macrophyte Myriophyllum spicatum, but that high-pressure washing is needed to effectively remove small-bodied organisms, including the exotic predatory zooplankter Bythotrephes longimanus.

Beyond the tactics of how to clean boats, I evaluate efforts to strategically place boat cleaning stations on the landscape. My results show that a common predictive model is limited in its ability to predict which uninvaded lakes cleaning stations should protect. Instead, it appears that placing cleaning stations at invaded lakes to block the transport of invasive propagules is generally more likely to reduce landscape-level spread than protecting uninvaded lakes.

Aquatic NIS are only one of many environmental and cultural factors that affect ecosystems and societal interactions with the natural environment. To put the importance of aquatic NIS in context with other potential drivers of change in GL fisheries over the next two decades, I interviewed experts on GL fisheries, asking them to predict changes and to identify the most likely drivers of the changes they predicted. This study revealed that changing cultural interests are the main reason for expected declines in GL fisheries, but that NIS are the predominant environmental driver of change.

The ecological and social issues surrounding NIS are complex and multi-faceted. As human populations grow, causing global environmental changes and taxing the supply of natural resources, the line separating ecological concerns from social ones is increasingly blurred. In this dissertation, I have included humans as a key component of the ecosystems of the GL region and considered the ecological effects of human actions with respect to their introduction of and intervention against aquatic NIS. In so doing, this dissertation presents several case studies of aquatic NIS in the GL with the aim of providing insights regarding opportunities and pitfalls for efforts to improve NIS policy and management.