Combining stereo‐video monitoring and physiological trials to estimate reef fish metabolic demands in the wild

Abstract

Organismal metabolic rates (MRs) are the basis of energy and nutrient fluxes through ecosystems. In the marine realm, fishes are some of the most prominent consumers.However, their metabolic demand in the wild (field MR [FMR]) is poorly documented, because it is challenging to measure directly. Here, we introduce a novel approach to estimating the component of FMR associated with voluntary activity (i.e., the field active MR [AMR field ]). Our approach combines laboratory-based respirometry, swimming speeds, and field-based stereo-video systems to estimate the activity of individuals.We exemplify our approach by focusing on six coral reef fish species, for which we quantified standard MR and maximum MR (SMR and MMR, respectively) in the laboratory, and body sizes and swimming speeds in the field. Based on the relationships between MR, body size, and swimming speeds, we estimate that the activity scope (i.e., the ratio between AMR field and SMR) varies from 1.2 to 3.2 across species and body sizes. Furthermore, we illustrate that the scaling exponent for AMR field varies across species and can substantially exceed the widely assumed value of 0.75 for SMR. Finally, by scaling organismal AMR field estimates to the assemblage level, we show the potential effect of this variability on community metabolic demand. Our approach may improve our ability to estimate elemental fluxes mediated by a critically

3D tracking reveals energy-distance trade-offs in two dominant grazers on a degraded coral reef

“…Therefore, measuring an animal's acceleration in all three dimensions provides a valuable proxy to infer energy expenditure while moving(Wilson et al 2006). Overall, we are con dent that our acceleration values are correct, as the swimming speeds for the two model species are well within the range of swimming speeds of other coral reef shes observed using stereo-video(Schiettekatte et al 2022). Despite the lack of available SMR data for the studied surgeon sh species, literature values for species of comparable size were previously utilized to estimate energy expenditure in Imperial Cormorants (Phalacrocorax atriceps) (GómezLaich et al 2011).…”

Temperature, species identity and morphological traits predict carbonate excretion and mineralogy in tropical reef fishes

“…It is thus unlikely that this estimate is representative of all species, particularly for tropical reef fishes. Current knowledge on the factorial activity scope of reef fishes is limited and this parameter is likely highly variable among taxa and across body size 79 , 81 . The use of a single value as scaling factor may thus potentially introduce large errors in the estimated carbonate excretion rates.…”

“…Improvements in the measurement of field metabolic rates in fishes 81 , 82 may soon allow updates to our models to predict carbonate excretion rates for fishes in their natural habitat. To do so, we must, however, consider the role of fish diet in carbonate production.…”

Can metabolic traits explain animal community assembly and functioning?

“…The difference between MMR and RMR is the aerobic scope (AS), which represents an organism's capacity to increase its MR above RMR to support activity, digestion, growth, and reproduction. Although field metabolic rate (FMR; the average MR of a free‐living animal) represents a highly relevant quantity, difficulties of obtaining FMR in a standardized fashion may preclude its applicability as a trait (although see Chung et al ., 2019; Schiettekatte et al ., 2022). All MR traits can be expressed as a slope and an intercept of their scaling relationship with body mass (both of which can serve as trait values), which is usually linear at the log–log scale, and all are applicable to taxa for which oxygen uptake (respiration) can be determined at rest or during exercise.…”