Sublethal Effects and Acute Toxicity of Imidacloprid on the American Lobster, Homarus americanus

This dissertation presents a comprehensive investigation into the effects of imidacloprid (IMI), a neonicotinoid insecticide, on postlarval and subadult female American lobsters Homarus americanus. With IMI emerging as a potential sea lice treatment in salmon aquaculture, this research evaluated the risks it could pose to a key nontarget species inhabiting shared coastal ecosystems. Integrating acute toxicity testing, behavioral assessments, physiological assays, and transcriptomic profiling, this study offers a multidimensional perspective on IMI's sublethal and molecular impacts. Acute toxicity exposure trials determined the 96-hour LC50 for postlarval lobsters, contextualizing subsequent low-dose exposures reflective of environmentally plausible concentrations. Subadult lobsters exposed to 0.3 and 30 μg/L IMI showed no significant changes in hemolymph biochemistry, despite notable behavioral impairments. This dissociation underscores the value of behavior as a sensitive and ecologically meaningful endpoint for contaminant impact. Postlarval lobsters exhibited significant reductions in foraging and exploratory behaviors at 30 μg/L IMI, which are key functions critical for survival and population recruitment in early life stages. RNA sequencing revealed dose-dependent transcriptional responses, including upregulation of stress response genes at higher exposures (600 μg/L), implicating cellular processes involved in detoxification, oxidative stress, and cuticle formation. Such molecular disruptions, particularly during development, may have lasting fitness consequences. Findings suggest that even sublethal concentrations of IMI can disrupt critical behaviors and molecular pathways in lobsters, particularly during sensitive developmental windows, with potential consequences for survival, recruitment, and long-term population health. Given the ecological and economic importance of H. americanus, these results raise serious concerns about the unintended risks of IMI use in coastal aquaculture settings. This research underscores the need for proactive environmental risk assessments that extend beyond mortality endpoints and demonstrates the value of integrating behavioral and transcriptomic tools to detect early-warning signs of ecological stress. Together, these findings provide a science-based foundation for regulatory decision-making and reinforce the importance of identifying safer, ecosystem-compatible alternatives for sea lice management in marine aquaculture.