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Invasive species are organisms moved from one region to another by humans. Although they are not always harmful to the recipient community, their lack of evolutionary history with their new community can set the stage for destruction. In a world of increasing interconnectivity and warming waters, we expect invasive species will continue to be introduced and that their ranges will expand as more areas become suitable habitats. At this critical point in our planet’s natural history, the need to understand where invasive species can survive and how to detect them are important. Here, I begin with a review of invasive species physiology measurements using species identified as invasive through the Marine Invader Monitoring and Information Collaborative. These data points highlight inconsistencies in measurement technique as well as the importance that acclimation temperature and life stage play on thermal thresholds. Based on the noise in the data, I recommend laboratory experiments to understand the absolute maximum and minimum survivable temperatures for each species, followed by field observations of temperatures needed to grow and reproduce. Then, using a newer invader to Maine Hemigrapsus sanguineus, I measured thermal thresholds for summer and winter-acclimated crabs and found shifts in thermal thresholds as well as evidence that winter temperatures are stressful for these crabs. Lastly, to effectively detect invasive species early, I tested and designed assays for environmental DNA (eDNA) detection of 9 invasive or nuisance species in the Gulf of Maine. Using laboratory experiments and a two-year time series in a local tide pool, I found that not all of the studied invertebrate species can be detected equally. Some organisms with soft, exposed tissues shed eDNA consistently with their abundance, while organisms with exoskeletons or shells do not. This trend does not hold true for all of the studied taxa, but this premise alongside an understanding of natural history and morphology helps clarify the observed trends. Thus, eDNA techniques should not be applied equally across all taxa for management purposes without a clear understanding of the message of the signal. Overall, I made recommendations to better predict suitable habitats for invasive species, characterized thresholds for an understudied invasive species in New England, and continued building upon the challenges of detecting invertebrates with eDNA. 

As global temperatures continue to rise, accurate predicted species distribution models will be important for forecasting the movement of range-shifting species. These predictions rely on measurements of organismal thermal tolerance, which can be measured using classical threshold concepts such as Arrhenius break temperatures and critical thermal temperatures, or through ecologically relevant measurements such as the temperature at which reproduction and growth occur. Many species, including invasive species, exhibit thermal plasticity, so these thresholds may change based on ambient temperature, life stage, and measurement techniques. Here, we review thermal thresholds for 15 invertebrate species invasive to the Gulf of Maine. The high degree of variability within a species and between applied conceptual frameworks suggests that modeling the future distribution of these species in all ecosystems, but especially in the rapidly warming northwest Atlantic and Gulf of Maine, will be challenging. While each of these measurement techniques is valid, we suggest contextualization and integration of threshold measurements for accurate modeling.