Temperature and acid-base balance in the American lobster Homarus americanus

Lobsters (Homarus americanus) in the wild inhabit ocean waters where temperature can vary over a broad range (0-25°C). To examine how environmental thermal variability might affect lobster physiology, we examine the effects of temperature and thermal change on the acid-base status of the lobster hemolymph. Total CO₂, pH, P_CO2 and HCO ₃^- were measured in hemolymph sampled from lobsters acclimated to temperature in the laboratory as well as from lobsters acclimated to seasonal temperatures in the wild. Our results demonstrate that the change in hemolymph pH as a function of temperature follows the rule of constant relative alkalinity in lobsters acclimated to temperature over a period of weeks. However, thermal change can alter lobster acid-base status over a time course of minutes. Acute increases in temperature trigger a respiratory compensated metabolic acidosis of the hemolymph. Both the strength and frequency of the lobster heartbeat in vitro are modulated by changes in pH within the physiological range measured in vivo. These observations suggest that changes in acid-base status triggered by thermal variations in the environment might modulate lobster cardiac performance in vivo.