COOKE SCHREIBER, S.M.*; JURY, S.; WATSON, W.H.: Seasonal differences in behavioral thermoregulation in the lobster, Homarus americanus.

Lobsters in the Great Bay estuary (NH) undergo a seasonal migration, possibly cued by changes in water temperature. Previous work on their thermal preference indicated that lobsters gravitate toward a final thermal preferendum slightly above normal summer conditions (Crossin et al., 1998). We conducted avoidance studies, during which lobsters were exposed to increasing temperatures (rate of change < 0.2�C/min) until they left their shelters. "Summer-acclimated" lobsters (~15�C) exhibited avoidance responses when the temperature reached ~22�C, well above their preferred range of 15-18�C. However, winter lobsters (ambient = ~4�C) exhibited avoidance behaviors at ~13.5�C, before the temperature reached their preferred levels. This suggests that avoidance behaviors are initiated by a relative increase in temperature (+7-9�C) rather than by exposure to an absolute temperature. Heart and ventilation rates also showed a linear increase in rate over most of the range of observed estuarine temperatures (Q10 = 1.8, 5-20�C). Thus, an increase of 7-9�C would approximately double their metabolism. Our working hypothesis is that, during these fairly rapid thermal increases, lobster movements are triggered by changes in metabolic rate, rather than sensory inputs indicating a rise in temperature or an absolute temperature. This study was supported by NOAA (SeaGrant) and the USDA (Hatch).