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EFFECT OF TEMPERATURE AND SALINITY ON THE OXYGEN CONSUMPTION OF TWO INTERTIDAL CRABS

1960; Marine Biological Laboratory (MBL); Volume: 118; Issue: 2 Linguagem: Inglês

10.2307/1538998

1939-8697

Paul A. Dehnel,

Environmental Toxicology and Ecotoxicology

1. Oxygen consumption measurements have been made on two species of crabs, Hemigrapsus oregonensis and H. nudus. These crabs were either brought from field conditions and measured directly, or acclimated to different combinations of temperature and salinity for two to three weeks prior to experimentation.2. Acutely measured seasonal rate-temperature curves for summer and winter animals of both species, kept at their seasonal salinity, have shown that summer animals at all temperatures over the physiological range have a higher weight-specific oxygen consumption than winter ones.3. Winter animals of both species are depressed at a lower temperature than summer ones, and depression at the high temperature begins at about the same point for both summer and winter crabs. Comparison of summer and winter animals of both species at 30° C. shows about the same amount of depression.4. Both species fail to show an acclimation shift on the ordinate, summer versus winter, but winter animals show an acclimation of the upper physiological limit.5. Acclimated rate-temperature curves for both species generally have a higher Q10 than either the summer or winter acutely measured curves.6. When summer crabs of both species are acclimated to a series of temperatures (5°, 10°, 15° and 20° C.) at either low salinity (25% sea water) or high salinity (75% sea water), it is seen that as the acclimation temperature increases, oxygen consumption decreases over most of the weight range. Statistical analysis shows. these changes in ordinal position of regression lines to be significant at the one per cent level of probability.7. In H. oregonensis, weight-specific oxygen consumption is higher when acclimated to 25% sea water, at all acclimation temperatures than when acclimated to 75% and at the same series of temperatures. In the case of H. nudus the respiratory rate is higher when crabs are acclimated to the low temperature, low salinity combination, when compared with low temperature, high salinity. At higher acclimation temperatures, crabs acclimated to 75% sea water have the higher rate. Statistical analysis of ordinal position of regression lines for both species shows them to be significant at the one per cent level.8. When H. oregonensis is acclimated to low salinity and any of the four acclimation temperatures, there is a differential size effect; weight-specific oxygen consumption of small crabs shows a proportionately greater change as acclimation temperature increases. And as acclimation temperature increases, size dependence decreases. Changes in slopes (b) for the total of the four acclimation temperature regression lines are significant at the one per cent level. If crabs are acclimated to the high salinity, no size effect is demonstrable. Comparison of the two acclimation salinities at each acclimation temperature also shows no size effect. For H. nudus, animals acclimated to low salinity and the four acclimation temperatures show no size effect, but at 75% sea water there is a demonstrable size effect. Weight-specific oxygen consumption of large animals shows a greater rate change at higher acclimation temperatures, and there is greater size dependence at these higher temperatures. Significance of the regression lines is at the five per cent level. No statistically significant differences in slope exist when the respiratory rate is compared for both salinities at each acclimation temperature.9. Positive linear regression coefficients for these experimental results range from 0.315 to 0.667. Only a few approach the reported 0.67 exponent. These data show that the regression coefficient is not an inherent species character, but is dependent upon intrinsic and extrinsic factors.10. Values of Q10 have been used to compare seasonal rate-temperature data, but show little consistency in relation to acutely measured responses as a function of increasing experimental temperature, size increase or seasonal difference. Similarly, the temperature and salinity acclimation data fail to show a definite trend for size increase or for increase in temperature at a given size. Generally, Q10 values increase at lower acclimation temperatures, at both salinities, and then decrease as the temperatures increase.11. Salinity affects the metabolic response of these two species of crabs to temperature. Weight-specific oxygen consumption is highest at the low temperature, low salinity combination. As temperature increases rate of oxygen consumption remains higher at the low salinity for H. oregonensis, but high salinity results in a higher rate for H. nudus. This greater response to low salinity is thought, in part, to be the result of increased work to maintain an osmotic balance. It does not result from increased muscular activity.12. Differential responses of Hemigrapsus to temperature and salinity, as measured by oxygen consumption and temperature tolerance, are suggested as a means by which H. nudus, in particular, became established in the geographic area of this study.