Abstract

BackgroundQuantifying metabolic rate in free-living animals is invaluable in understanding the costs of behaviour and movement for individuals and communities. Dynamic body acceleration (DBA) metrics, such as vectoral DBA (VeDBA), are commonly used as proxies for the energy expenditure of movement but are of limited applicability for slow-moving species. It has recently been suggested that metrics based on angular velocity might be better suited to characterise their energetics. We investigated whether a novel metric—the ‘Rate of change of Rotational Movement (RocRM)’, calculated from the vectoral sum of change in the pitch, roll and yaw/heading axes over a given length of time, is a suitable proxy for energy expenditure.ResultsWe found that RocRM can be used as an alternative energy expenditure proxy in a slow-moving benthic invertebrate. Eleven Giant spider conchs Lambis truncata (collected in the Red Sea) were instrumented with multiple channel (Daily Diary) tags and kept in sealed chambers for 5 h while their oxygen consumption, V̇O2, was measured. We found RocRM to be positively correlated with V̇O2, this relationship being affected by the time-step (i.e. the range of the calculated differential) of the RocRM. Time steps of 1, 5, 10 and 60 s yielded an explained variability of between 15 and 31%. The relationship between V̇O2 and VeDBA was not statistically significant, suggesting RocRM to provide more accurate estimations of metabolic rates in L. truncata.ConclusionsRocRM proved to be a statistically significant predictor of V̇O2 where VeDBA did not, validating the approach of using angular-based metrics over dynamic movement-based ones for slower moving animals. Further work is required to validate the use of RocRM for other species, particularly in animals with minimally dynamic movement, to better understand energetic costs of whole ecosystems. Unexplained variability in the models might be a consequence of the methodology used, but also likely a result of conch activity that does not manifest in movement of the shell. Additionally, density plots of mean RocRM at each time-step suggest differences in movement scales, which may collectively be useful as a species fingerprint of movement going forward.

Highlights

  • Quantifying metabolic rate in free-living animals is invaluable in understanding the costs of behaviour and movement for individuals and communities

  • We investigate the validity of a new metric, derived from the rates of change in rotational movement, as an alternative to Dynamic body acceleration (DBA) for estimating energy expenditure in a slow-moving benthic invertebrate, the Giant spider conch, L. truncata

  • Differences in movement traces between vectoral DBA (VeDBA) and Rate of change of Rotational Movement (RocRM) Movement data traces of rotational movement axes, VeDBA and RocRM reveal appreciable differences in the RocRM signal with different movement types (Fig. 2). ­RocRM10 movement peaks differed between movements predominantly in the pitch and roll axes, exhibiting split peaks, and those predominantly in the heading/yaw axis, exhibiting peaks that are more singular

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Summary

Introduction

Quantifying metabolic rate in free-living animals is invaluable in understanding the costs of behaviour and movement for individuals and communities. Labelled water (DLW)—measuring the rate of ­CO2 production, VCO2 [10,11,12]—is the only direct measure, while other methods, such as recording heart rate, use proxies for energy expended [10, 13, 14]. A fairly recent approach has used tri-axial accelerometers in externally attached tags to provide a less invasive and high-resolution alternative deriving ‘dynamic body acceleration’ (DBA) as a proxy for movement-based energy expenditure [17, 18]. DBA is calculated from the dynamic acceleration (i.e. the acceleration signal that remains following the subtraction of static acceleration, or the gravitational component [19]) summed over all three dimension axes (x, y, z; surge, heave, sway) [20, 21]

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