Effet de la temperature sur le comportement des larves de stade IV du homard Americain (Homarus americanus)

The American lobster (Homarus americanus) is a common species found along the East coast of North America, from the Strait of Belle Isle between Labrador and Newfoundland (Canada) to Cape Hatteras in North Carolina (United States). It is, however, more abundant in the southern part of the Gulf of St. Lawrence as well as off the coast of Nova Scotia in Canada and in the Gulf of Maine in the United States. The life cycle of the American lobster has an important pelagic phase where stage IV larvae represent the competent stage (transition phase). The lobster larva, at that time, leaves the pelagic habitat for the benthic habitat. Once on the bottom, the larva rapidly seeks a shelter to limit its vulnerability to predators.;The American lobster may be affected by many environmental parameters. As for most marine invertebrates, the survival, the length of each stage of the life cycle and the behavior may be influenced by the thermal regime. The main objective of this study is to describe in laboratory the time budget of stage IV lobster larvae in relation with temperature. The effect of acclimation to a given temperature on the time budget of larvae is studied as well.;Two acclimation temperatures were used (15 and 20°C). Acclimated larvae were subsequently subjected to three temperature exposures (10, 15 and 20°C) and their behavior observed. A single larva was used in the experimental enclosures in assays conducted in 2009. These observations were compared with those obtained the following summer when a group of larvae was used (5 larvae per assay) under the same temperature conditions to determine whether a larva within a group reacts similarly to an isolated larva.;The time budget established in 2009 (1 larva per aquarium) showed that the percentage of time a larva was hiding was high regardless of the treatment (acclimation and temperature exposure) and the larval batch (larval cohort from the hatchery) compared to other observed behaviors (e.g. swimming, surface swimming and exploration). However, results showed more variability when larvae were acclimated at 15°C. The percentage of time a larva remained hidden was similar for all treatments observed in 2009. Larvae tended to hide quickly in warm water (20°C). In cold water (10°C), larvae tended to hide more rapidly if acclimated at 15°C. They, however, left their shelters more often. Larvae took a longer period of time to hide in cold water (10°C) when they were acclimated at 20°C. They, however, left their shelter less often. Larvae displayed a tail-flick behavior when stressed. This behavior was common in cold water, especially for larvae acclimated at 20°C and exposed to a temperature of 10°C.;The time budgets observed in 2010 (5 larvae per aquarium) remained similar to those observed in 2009 (1 larva per aquarium). A higher variability was, however, observed in 2010. The percentage of time a larva was hiding was low in cold water (10°C). Larvae tended to hide quickly when exposed to a high temperature in comparison to the acclimation temperature. Tail-flicks were observed in larvae acclimated at 20°C and exposed to 10°C, as observed in 2009, but also for larvae acclimated at 15°C and exposed to 10°C. Results showed that the number of larvae did not affect the behavior of the larvae significantly (few interactions between individuals).;Our results show that the behavior of stage IV American lobster larvae was affected by water temperature. Cold water affects the larval physiology as well as the general behavior including the search for a shelter. Behavioral modifications induced by temperature could increase the vulnerability of larvae to predators. Acclimation to cold water appears to decrease this effect and could increase their survival in the wild. This information should be useful to the American lobster industry. The industry has tried for many years to improve its enhancement techniques to increase lobster stocks in the coastal habitat. Larval acclimation before their release in the natural environment could improve the survival of larvae and enhance lobster recruitment.