SENSITIVITY OF CRABS CALLINECTES-SAPIDUS AND C-SIMILIS AND THE GASTROPOD STRAMONITA-HAEMASTOMA TO HYPOXIA AND ANOXIA

Tolerances of the juvenile blue crab Callinectes sapidus Rathbun, lesser blue crab Callinectes similis Williams and the adult southern oyster drill Stramonita haemastoma Linnaeus to long-term (28 d) hypoxia and short-term (10 d) changes from normoxia to hypoxia and back to normoxia were monitored at 24-degrees-C and 30 parts per thousand S. C. sapidus was very sensitive to hypoxia with a 28 d LC50 of 106 Torr 02. All C. sapidus in 25 and 0 Torr 02 died within 6 d of exposure. C similis exhibited lesser sensitivity to hypoxia with a 28 d LC50 of 43 Torr 02. All Crabs exposed to anoxic water died within 3 d of exposure. S. haemastoma exhibited a 28 d LC50 Of 11.5 Torr 02. Under anoxia, initial death occurred in S. haemastoma after Day 11 and complete mortality occurred by Day 22. No significant difference occurred in the feeding rates of blue crabs exposed to normoxia, 119 and 73 Torr 02, but these rates were significantly higher than that in blue crabs exposed to 50 Torr 02. Feeding rates in the lesser blue crab exposed to 50 and 25 Torr 02 were significantly lower than in crabs exposed to 119 Torr 02 and normoxia. Growth and molting rates in both species of crabs were significantly higher in the normoxic exposure than in those exposed to hypoxia and anoxia. Significant differences were noticed in the feeding rate of S. haemastoma exposed to hypoxia from those exposed to normoxia. Feeding rate in S. haemastoma declined linearly with declining 02 Concentration. Mean oxygen consumption rates of C sapidus exposed to 25 and 50 Torr 02 were lower than the normoxic consumption but this rate was higher in the crabs exposed to 115 Torr 02. Mean oxygen consumption rate of C similis exposed at all hypoxic levels was higher than of those exposed to normoxia, indicating overcompensation. The transfer experiment was performed only on C. sapidus. The feeding rate of crabs exposed to different hypoxic levels was not significantly different from those exposed to normoxia but the feeding rate increased sharply upon transfer of the juvenile blue crabs to normoxic water after 10 d hypoxic exposure and may have been due to partial starvation during hypoxic exposure. Number of molts after transfer to normoxia was higher in all the crabs exposed to hypoxia compared to those exposed to normoxia. Sensitivity to hypoxia can be ranked as C. sapidus > C. similis > S. haemastoma.