Normoxic and anoxic energy metabolism of the southern oyster drillThais haemastoma during salinity acclimation

The energetic cost associated with salinity acclimation was determined in the marine gastropodThais haemastoma by direct calorimetry under normoxic and anoxic conditions. Snails were collected from Caminada Pass near Grand Isle, Louisiana (Longitude 90°2W; Latitude 29°2N) in September 1987. Metabolic heat flux of snails acclimated to and measured at 10 or 30 S was similar at 15.06 or 16.39 J g^–1 dry wt h^–1, respectively, (corresponding to 0.76 or 0.83 ml O₂ g^–1 dry flesh wt h^–1) under normoxic conditions, and 2.39 or 2.53 J g^–1 dry wt h^–1 under anoxic conditions. Inter-individual variability was high, obscuring the effect of salinity gradient on heat flux. When standardized to the pre-transfer control level of each individual under anoxic conditions, a significant increase (55%) of energy expenditure was observed for snails transferred to hyperosmotic conditions. In contrast, heat flux varied insignificantly in individuals in the anoxic 30 to 10 S transfer. After transfer of individuals from 10 to 30 S under normoxic conditions, heat flux was depressed initially to 38% of the control rate, but recovered after 14 h to a higher metabolic rate (56%) than the pre-transfer control rate. After transfer of individuals from 30 to 10 S under normoxic conditions, the standardized heat flux decreased to 28% of the control rate, followed by a 20 h period of recovery to the control rate. The energy cost of intracellular hypoosmotic regulation was less than hyperosmotic regulation under anoxic conditions. The retraction of the foot ofT. haemastoma after normoxic salinity transfers did not generally correlate with the time course of metabolic heat flux.