SUMMARYMetabolic rates of aquatic organisms are estimated from measurements of oxygen consumption rates (Ṁ O2 ) through swimming and resting respirometry. These distinct approaches are increasingly used in ecophysiology and conservation physiology studies; however, few studies have tested whether they yield comparable results. We examined whether two fundamental Ṁ O2 measures, standard metabolic rate (SMR) and maximum metabolic rate (MMR), vary based on the method employed. Ten bridled monocle bream (Scolopsis bilineata) were exercised using (1) a critical swimming speed (U crit ) protocol, (2) a 15min exhaustive chase protocol and (3) a 3min exhaustive chase protocol followed by brief (1min) air exposure. Protocol 1 was performed in a swimming respirometer whereas protocols 2 and 3 were followed by resting respirometry. SMR estimates in swimming respirometry were similar to those in resting respirometry when a three-parameter exponential or power function was used to extrapolate the swimming speed-Ṁ O2 relationship to zero swimming speed. In contrast, MMR using the U crit protocol was 36% higher than MMR derived from the 15min chase protocol and 23% higher than MMR using the 3min chase/1min air exposure protocol. For strong steady (endurance) swimmers, such as S. bilineata, swimming respirometry can produce more accurate MMR estimates than exhaustive chase protocols because oxygen consumption is measured during exertion. However, when swimming respirometry is impractical, exhaustive chase protocols should be supplemented with brief air exposure to improve measurement accuracy. Caution is warranted when comparing MMR estimates obtained with different respirometry methods unless they are cross-validated on a species-specific basis.

Tropical coral reef teleosts are exclusively ectotherms and their capacity for physical and physiological performance is therefore directly influenced by ambient temperature. This study examined the effect of increased water temperature to 3 1C above ambient on the swimming and metabolic performance of 10 species of damselfishes (Pomacentridae) representing evolutionary lineages from two subfamilies and four genera. Five distinct performance measures were tested: (a) maximum swimming speed (U crit ), (b) gait-transition speed (the speed at which they change from strictly pectoral to pectoral-and-caudal swimming, U pÀc ), (c) maximum aerobic metabolic rate (MO 2ÀMAX ), (d) resting metabolic rate (MO 2ÀREST ), and (e) aerobic scope (ratio of MO 2ÀMAX to MO 2ÀREST , A SC ). Relative to the control (29 1C), increased temperature (32 1C) had a significant negative effect across all performance measures examined, with the magnitude of the effect varying greatly among closely related species and genera. Specifically, five species spanning three genera (Dascyllus, Neopomacentrus and Pomacentrus) showed severe reductions in swimming performance with U crit reduced in these species by 21.3-27.9% and U pÀc by 32.6-51.3%. Furthermore, five species spanning all four genera showed significant reductions in metabolic performance with aerobic scope reduced by 24.3-64.9%. Comparisons of remaining performance capacities with field conditions indicate that 32 1C water temperatures will leave multiple species with less swimming capacity than required to overcome the water flows commonly found in their respective coral reef habitats. Consequently, unless adaptation is possible, significant loss of species may occur if ocean warming of ! 3 1C arises.

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°S and 14°S) and maintained at one of four temperatures (24, 27, 30, 33 °C). Following >4 weeks acclimation, the spontaneous swimming speeds and activity patterns of individuals were recorded over a period of 12 days. At 24-27 °C, spontaneous swimming speeds of common coral trout were 0.43-0.45 body lengths per second (bls(-1)), but dropped sharply to 0.29 bls(-1) at 30 °C and 0.25 bls(-1) at 33 °C. Concurrently, individuals spent 9.3-10.6% of their time resting motionless on the bottom at 24-27 °C, but this behaviour increased to 14.0% at 30 °C and 20.0% of the time at 33 °C (mean ± SE). The impact of temperature was greatest for smaller individuals (<45 cm TL), showing significant changes to swimming speeds across every temperature tested, while medium (45-55 cm TL) and large individuals (>55 cm TL) were first affected by 30 °C and 33 °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 °C and 33 °C, while the low-latitude population only showed significant reductions at 33 °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.