What makes marine turtles go: A review of metabolic rates and their consequences

Quantification of metabolic rates (MR) is fundamental to understanding an individual organism's physiology and life history, as well as overall population dynamics. Applications of MR measurements have increased both in quantity and quality across animal ecology over the past 50 years. Included in this trend, research on MRs of marine turtles and its consequences for these unique ectothermic vertebrates has matured significantly. We reviewed existing literature on marine turtle MRs in the context of the physiology, ecology, and life history of these animals. Metabolic rates have been obtained and published for 4 of 7 marine turtle species, but not for all life stages for all of these species. Studies of marine turtle metabolism have ranged from straightforward MR measurements of a few individuals to use of innovative techniques to estimate energy expenditure of natural activities and for applications to marine turtle energetics and diving physiology. Comparisons of allometric relationships between resting MR (RMR) and body mass for leatherbacks (Dermochelys coriacea), green turtles (Chelonia mydas), other reptiles, and mammals revealed no differences between leatherbacks and green turtles, nor between those species and other reptiles, but significant differences with mammals. In addition, we synthesized research on the thermal biology of the leatherback turtle, which ranges from temperate to tropical waters, and concluded that leatherbacks achieve and maintain substantial differentials between body and ambient temperatures in varied thermal environments through an integrated balance of adaptations for heat production (e.g., adjustments of MR) and retention. Finally, we recommend that future research should 1) address remaining data gaps in current knowledge of MRs of some species, 2) apply MR measurements to important physiological, ecological, and conservation topics, 3) investigate cellular metabolism of marine turtles, and 4) focus on quantification of at-sea energy expenditure incurred by marine turtles during natural activities.