Increasing ocean temperatures reduce activity patterns of a large commercially important coral reef fish

Large-bodied fish are critical for sustaining coral reef fisheries, but little is known about the vulnerability of these fish to global warming. This study examined the effects of elevated temperatures on the movement and activity patterns of the common coral trout Plectropomus leopardus (Serranidae), which is an important fishery species in tropical Australia and throughout the Indo West-Pacific. Adult fish were collected from two locations on Australia's Great Barrier Reef (23 degrees S and 14 degrees S) and maintained at one of four temperatures (24, 27, 30, 33 degrees C). Following >4weeks acclimation, the spontaneous swimming speeds and activity patterns of individuals were recorded over a period of 12days. At 24-27 degrees C, spontaneous swimming speeds of common coral trout were 0.43-0.45 body lengths per second (bls(-1)), but dropped sharply to 0.29bls(-1) at 30 degrees C and 0.25bls(-1) at 33 degrees C. Concurrently, individuals spent 9.3-10.6% of their time resting motionless on the bottom at 24-27 degrees C, but this behaviour increased to 14.0% at 30 degrees C and 20.0% of the time at 33 degrees C (mean +/- SE). The impact of temperature was greatest for smaller individuals (<45cm TL), showing significant changes to swimming speeds across every temperature tested, while medium (45-55cm TL) and large individuals (>55cm TL) were first affected by 30 degrees C and 33 degrees C, respectively. Importantly, there was some indication that populations can adapt to elevated temperature if presented with adequate time, as the high-latitude population decreased significantly in swimming speeds at both 30 degrees C and 33 degrees C, while the low-latitude population only showed significant reductions at 33 degrees C. Given that movement and activity patterns of large mobile species are directly related to prey encounter rates, ability to capture prey and avoid predators, any reductions in activity patterns are likely to reduce overall foraging and energy intake, limit the energy available for growth and reproduction, and affect the fitness and survival of individuals and populations.