Effects of temperature and body-mass on the standard metabolic rates of the round stingray, Urobatis halleri (Cooper, 1863)

Abstract Using an intermittent respirometer, we measured the thermal sensitivity (metabolic Q10) and scaling relationship (b) of the round stingray, Urobatis halleri, based on their standard metabolic rates (SMR). A total of 33 individuals (mass range = 0.03–0.86 kg) were acclimated for over 14 days at three temperature treatments (15°, 23°, 27 °C) spanning the seasonal water temperature variation in southern California. An average thermal sensitivity (Q10) of 3.1 was estimated for the round stingray across the range of experimental temperatures. Estimations of size dependent Q10 was 3.8 in juveniles while 2.6 in adults. Our model showed a negative relationship between this species mass-specific scaling exponent (b) and temperature (b = 0.99 at 15 °C, b = 0.86 at 23 °C, and b = 0.79 at 27 °C). Results indicate that the round stingray is relatively sensitive to the thermal fluctuations they experience in southern California. While adults with a relatively high metabolic Q10 may optimize their daily net energy gain by exploiting the local thermal heterogeneity, a higher thermal sensitivity in juveniles could have adverse effects on the population fitness under a pervasive increase of ocean's temperature. Given that the scaling exponent can be affected by temperature, modeling studies should consider correcting for this effect when using scaling relationships as an input for more precise bioenergetic models under various thermal scenarios.