Global warming is expected to reduce body sizes of ectothermic animals. Although the underlying mechanisms of size reductions remain poorly understood, effects appear stronger at latitudinal extremes (poles and tropics) and in aquatic rather than terrestrial systems. To shed light on this phenomenon, we examined the size dependence of critical thermal maxima (CTmax) and aerobic metabolism in a commercially important tropical reef fish, the leopard coral grouper (Plectropomus leopardus) following acclimation to current-day (28.5 °C) vs. projected end-of-century (33 °C) summer temperatures for the northern Great Barrier Reef (GBR). CTmax declined from 38.3 to 37.5 °C with increasing body mass in adult fish (0.45–2.82 kg), indicating that larger individuals are more thermally sensitive than smaller conspecifics. This may be explained by a restricted capacity for large fish to increase mass-specific maximum metabolic rate (MMR) at 33 °C compared with 28.5 °C. Indeed, temperature influenced the relationship between metabolism and body mass (0.02–2.38 kg), whereby the scaling exponent for MMR increased from 0.74 ± 0.02 at 28.5 °C to 0.79 ± 0.01 at 33 °C, and the corresponding exponents for standard metabolic rate (SMR) were 0.75 ± 0.04 and 0.80 ± 0.03. The increase in metabolic scaling exponents at higher temperatures suggests that energy budgets may be disproportionately impacted in larger fish and contribute to reduced maximum adult size. Such climate-induced reductions in body size would have important ramifications for fisheries productivity, but are also likely to have knock-on effects for trophodynamics and functioning of ecosystems.

Item Type:	Refereed Article
Keywords:	climate warming, fish size, fisheries, body size, climate change, critical thermal maximum, Great Barrier Reef, metabolic rate, Plectropomus leopardus, thermal tolerance
Research Division:	Biological Sciences
Research Group:	Zoology
Research Field:	Animal physiological ecology
Objective Division:	Environmental Management
Objective Group:	Coastal and estuarine systems and management
Objective Field:	Coastal or estuarine biodiversity
UTAS Author:	Clark, TD (Dr Timothy Clark)
ID Code:	116098
Year Published:	2017
Web of Science® Times Cited:	58
Deposited By:	Fisheries and Aquaculture
Deposited On:	2017-05-01
Last Modified:	2018-03-21
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