Monitoring and managing the spread of marine introduced species: Development of approaches and application to the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus)

Managing introduced species, a current environmental problem, is hindered by real-world limitations of personnel, data, and funding. Monitoring is an important precursor to effective management because detecting an introduced species when its population is localized and at low density (i.e., early detection) maximizes the probability of successful eradication. Often introduced species are only detected years after the initial introduction, when eradication is no longer a viable option. Therefore, in this thesis we developed and analyzed techniques to better monitor and model the spread of the European green crab (Carcinus maenas) and the Asian shore crab ( Hemigrapsus sanguineus). To overcome issues of insufficient amounts of data and personnel, we recruited nearly a thousand volunteers and validated their ability to identify introduced and native species of crabs with high levels of accuracy (Chapter 1). To increase the probability of early detection, we need to not only increase sampling intensity, but also to identify more effective and efficient sampling techniques. Therefore, we developed a quantitative, standardized experimental field approach for comparing the sensitivity of different sampling techniques for detecting organisms at low densities (Chapter 2). Even with an efficient sampling technique and increased resources of a validated volunteer monitoring network, we are still not adequately equipped for early detection monitoring on the large-scale. Since it is infeasible to monitor everywhere a species could be introduced, we should monitor where they are more likely to arrive and manage them where their impact will be greatest. To address this problem we modified an oceanographic model, incorporated biological behaviors, used extensive field data to parameterize and validate the model's ability to forecast areas that are most likely to be colonized, so we can optimally allocate our limited resources (Chapter 3). Finally, to determine what areas will be most impacted, we quantified the population densities of these two invasive species and their incidences of injury, which is mainly due to inter- and intraspecific aggression. We propose that injury is an important, but understudied, moderating factor of the impacts of invasive species (Chapter 4). This research increases our ability to monitor and manage the spread of introduced species.