Individual variability in stable isotope turnover rates of epidermal mucus according to body size in an omnivorous fish
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PRIMARY RESEARCH PAPER
Individual variability in stable isotope turnover rates of epidermal mucus according to body size in an omnivorous fish Emily R. Winter
. J. Robert Britton
Received: 3 December 2019 / Revised: 25 May 2020 / Accepted: 15 October 2020 Ó The Author(s) 2020
Abstract Epidermal mucus (‘mucus’) is increasingly applied to fish ecological studies based on stable isotope analysis (SIA) due to its non-invasive collection. However, knowledge on mucus SI turnover rates of individual fish remains limited, including uncertainty over how they are influenced by fish body sizes. Here, a diet switch experiment predicted mucus SI turnover rates (d13C and d15N) as a function of time using samples taken over 200 days from 10 individually tagged common carp Cyprinus carpio covering two size groups. Non-linear mixed effects models revealed rapid turnover of both d13C and d15N (T50: 2–5 days; T95: 9–22 days); d15N turnover rates were slower for the larger cohort, while d13C turnover rates were independent of body size. Within size groups, turnover rates were not expected to vary between individuals. These experimental results suggest that due to these fast turnover rates, epidermal mucus can provide insights into the diets of fish over very short
Handling editor: Michael Power
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-020-04444-2) contains supplementary material, which is available to authorised users. E. R. Winter (&) J. R. Britton Institute of Aquatic Sciences, Department of Life and Environmental Sciences, Bournemouth University, Poole, Dorset BH12 5BB, UK e-mail: [email protected]
timeframes, although for d15N the body size of the fish needs consideration. Keywords Half-life Isotopic incorporation Diet switch Non-invasive sampling Trophic discrimination factor
Introduction The ecological application of stable isotope analyses (SIA) of consumer tissues has become a fundamental component of studies assessing the dietary sources and trophic levels of aquatic organisms (Peterson & Fry, 1987; Hobson, 1999). Integral to the ecological interpretation of SIA data is the understanding of stable isotope turnover rates, especially their variation across tissue-types within organisms (Tieszen et al., 1983; Winter et al., 2019a). For example, SI turnover rates in fish are considerably slower in scales than the more metabolically active dorsal muscle (e.g. Busst & Britton, 2018). Consequently, in SI studies aiming to quantify temporal prey resource use, understanding the dietary timescales represented by the analysed tissue(s) is crucial in the evaluation process (Vander Zanden et al., 2015). Stable isotope turnover rates can also vary according to the body size of individuals (Thomas & Crowther, 2015; Vander Zanden et al., 2015). Multi-
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Hydrobiologia
taxa reviews suggest that the SI half-life, defined as the time to reach 50% equilibrium with the diet, increases with body mass (Weidel et
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