The behavior of stage IV American lobster (Homarus americanus) larvae in relation to various water temperatures was observed in laboratory. Time budgets were documented in 2009 in trials using a single larva per experimental enclosure in relation to three temperature exposures (10°C. 15°C. and 20°C). Larvae acclimated at a given temperature (15°C and 20°C) were used. The same treatments were used in 2010, where one larva was observed within a group of five individuals per experimental enclosure. Larvae took less time to hide when they were acclimated to 15°C and then exposed to 20°C. Video observations showed that larvae were stressed (repeated tail flicks) when treatments simulated important heat shocks (e.g., larvae acclimated at 20°C and exposed to 10°C). Results for single larva were similar to those from groups of larvae. The tail-flicks display was also observed in 2010 with larvae acclimated at 15°C and then exposed to 10°C. Observations from both years showed that the time budget was similar regardless of the larval cohort used in trials (different brood stocks and times of the season). Overall, results confirm that water temperature affects the behavior of lobster larvae. Acclimation to a given temperature, however, tends to show that larvae may acclimate to cold water. This study provides interesting results to better understand the ecology of American lobster, particularly at the time of settlement. These results should also be of interest for the lobster industry, which looks to improve stock enhancement procedures through, for instance, lobster-stocking programs.