P3.112 Friday, Jan. 6 Living It Up Before Going Down- Vertical Positioning Behaviors of Homarus americanus Larvae in Response to a Thermocline MEYERS, M.L.*; JACOBS, M.W.; GALLAGER, S.M.; CHRISTMAS, A.F.; McDaniel College; McDaniel College; Woods Hole Oceanographic Institution; Western Washington University email@example.com
Vertical positioning of the larvae of the American lobster (Homarus americanus) is a critical factor that may influence transport, depth at settlement, and abundance. We hypothesized that vertical positioning behavior of lobster larvae would vary with larval age, and that vertical movements of larvae would be limited by the natural oceanographic barriers, such as thermoclines. Larvae of different stages were released into ten meter columns in one of three environments: (1) a column with an established thermocline, (2) a column with an evenly distributed water temperature undergoing the development of a thermocline, or (3) a column exhibiting a uniform temperature. We used an underwater video camera to profile vertical position as a function of temperature and time of day (day vs. night). Larvae of all three stages positioned themselves at significantly higher depths in the presence of a thermocline. Stage I larvae positioned themselves at higher depths at night than during the day, while stage III larvae and stage IV postlarvae were found at similar depths at night and during the day. Additionally, when larvae were released into an environment as a thermocline was forming, they responded to the formation by positioning themselves at higher depths over time. Postlarvae offered settlement habitats at a range of depths chose to settle above the thermocline if present and at lower depths in the absence of a thermocline. Although they were physically able to cross the thermocline, lobster larvae and postlarvae responded to the gradient by adjusting their vertical positioning. These results suggest that vertical positioning may be strongly influenced by natural barriers present in the open ocean.