Low-dose imidacloprid exposure reduces defensive behaviors in adolescent American lobsters, Homarus americanus

Behavior integrates sensory, neural, and physiological processes and links environmental conditions to organismal fitness. Neuroactive anthropogenic contaminants, such as the neonicotinoid imidacloprid (IMI), represent an emerging threat to aquatic ecosystems because they can disrupt these processes at concentrations far below those intended to kill target pests. Here, we tested whether low, sublethal concentrations of IMI impairs fitness-relevant behavior and physiology in adolescent American lobsters (Homarus americanus), an important benthic predator and species of high ecological, economic, and cultural importance. Female lobsters (mean carapace length = 81.5 mm) were exposed for 120 min to 0, 0.3, or 30 µg/L IMI, chosen to represent concentrations substantially below lethal insecticidal doses. Defensive and locomotor behaviors were assessed immediately following exposure and after a five-day recovery period, alongside measurements of hemolymph L-lactate, crustacean hyperglycemic hormone (CHH), and total protein. Lobsters exposed to IMI exhibited significant reductions in defensive behaviors in a dose-dependent manner, including tail flipping, meral spreading, pleopod fanning, and righting performance, with some impairments persisting after the recovery period. In contrast, hemolymph biochemical endpoints did not differ significantly among treatments for either time point. This dissociation indicates that behavior provides a more sensitive measure of functional impairment than commonly used physiological stress markers. Given the central role of these behaviors in survival, competition, and reproduction, even sublethal exposure may have important ecological and fitness consequences. Incorporating behavioral endpoints into environmental monitoring and risk assessment frameworks will strengthen One Ocean Health approaches to managing emerging chemical stressors.