TEMPERATURE EFFECTS ON BLOOD-OXYGEN EQUILIBRIA IN RELATION TO MOVEMENTS OF THE BAT RAY, MYLIOBATIS-CALIFORNICA IN TOMALES BAY, CALIFORNIA

In vitro blood-oxygen binding curves for the bat ray, Myliobatis calif ornica, were constructed at four temperatures (8, 14, 20, and 26-degre es-C) to gain insight into the possible adaptations to ambient tempera ture regimes in Tomales Bay, California. The curves were hyperbolic (m ean n50: 1.06) with high affinities (p50: 0.8-3.2 kPa) and large whole blood buffer values (beta: -14.25 to -16.43 slykes) implying a tolera nce to hypoxia and hypercapnia while large O2 capacities (CBO2: 3.1-4. 1 mmol.L-1) and Bohr factors (PHI: -0.45 to -0.52) indicated high acti vity levels. The temperature effect (DELTAH) was greatest between 14 a nd 20-degrees-C as compared to relatively temperature independent bind ing between the 8 to 14-degrees-C, and 20 to 26-degrees-C ranges. The heightened sensitivity between 14 and 20-degrees-C parallels a previou sly-documented large change in respiratory demand for this same temper ature range (Q10 = 6.81). However, the magnitude of the hematological adjustments were small relative to the large increase in metabolic dem and and it is likely that increasing cardiac output plays an important role to safeguard oxygen transport as temperature rises. Thus, the mo vements of rays between warmer and cooler regions of Tomales Bay are n ot related to their blood oxygen binding characteristics, but may be d ue to other factors such as increasing assimilation efficiency, minimi zing energy expenditure, or social factors.