Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

William B. Stickle, Jr

Abstract

This study measured the physiological and biochemical changes associated with exposure of the juvenile blue crab, Callinectes sapidus Rathbun and the lesser blue crab. C. similis Williams, to long term (28 d) hypoxia, short term (10 d) transfer from hypoxia to normoxia and a diurnally fluctuating oxygen regime for 28 days. The southern oyster drill, Stramonita haemastoma Linnaeus, was also exposed to 28 days of constant hypoxia to compare the responses of a tolerant species with the two species of Callinectes. The 28 day LC$\sb{50}$ estimates for C. sapidus, C. similis and S. haemastoma were respectively 106, 43 and 11.5 Torr under constant hypoxic exposure for 28 d. Feeding rates for the crabs of both species exposed to 50 and 25 Torr oxygen were significantly lower than for crabs exposed to higher levels of oxygen. Growth and molting rates of crabs exposed to constant hypoxia were always lower than for crabs exposed to normoxia. Feeding rate in S. haemastoma declined linearly with declining oxygen under constant exposure to hypoxia. Oxygen consumption rates of the two crab species under various hypoxic levels were significantly different. Mean oxygen consumption in C. similis exposed to hypoxia was higher than for crabs exposed to normoxia. Rate of adaptation for blue crabs transferred from hypoxia to normoxia was faster than when transferred from normoxia to hypoxia. Detection and avoidance of hypoxic water by the two species of crabs was also observed under laboratory conditions. Both species of crabs were able to detect and avoid hypoxic water and stay at an intermediate oxygen tension. Crabs were found to be more active at higher oxygen tensions. The feeding rate of C. sapidus exposed to diurnally varying oxygen tension was significantly higher than for the crabs exposed to normoxia while the feeding rate of C. similis exposed to diurnally varying oxygen tension was significantly lower than the ones exposed to normoxia. RNA and DNA concentration decreased over time in both species of crabs exposed to diurnal variation in oxygen tension. Concentration of the individual nucleic acids were found to be a reliable measure of hypoxia stress than the RNA:DNA ratio.

Pages

118

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