Effects of temperature and salinity on resting metabolism in two South African rock pool fish: the resident gobiid Caffrogobius caffer and the transient sparid Diplodus sargus capensis
Intertidal rock pools are inherently dynamic environments that experience marked changes in physico-chemical parameters over diel, tidal and seasonal time scales. Fish that inhabit the intertidal zone can generally be characterized as either permanent residents or transients/visitors. This study investigates the resting metabolic rate (RMR; mg O2 g/h) of the resident rock pool fish Caffrogobius caffer and the transient sparid Diplodus sargus capensis at a range of salinities (5, 15, 25, 35 and 45 PSU) and temperatures (14, 20 and 28°C) using closed-vessel respirometry. Both species were temperature sensitive, with Q10 (14–28) of 1.82 and 2.07, respectively. A significant positive relationship (P =0.03) between salinity and oxygen consumption was determined for D. sargus capensis, but not for C. caffer. The RMR values were significantly higher (P < 0.01) for D. sargus capensis compared to C. caffer at all temperatures and at all salinities, except 5 PSU. This was attributed to the different biologies of the two species, C. caffer being a bottom-dwelling species and D. sargus capensis a mid-water species. It is suggested that the decreased temperature sensitivity and euryhaline characteristics of C. caffer compared to D. sargus capensis, would allow the former to more effectively penetrate the upper intertidal zone.
Key words: resting metabolic rate, temperature, salinity, rock pool fish.