Elemental turnover rates and trophic discrimination in juvenile Lebranche mullet Mugil liza under experimental conditions

Abstract

The aim of this study was to determine the isotopic-turnover rate (R ) and trophic-discrimination factor (F ) in muscle tissues of Lebranche mullet Mugil liza fed an experimental diet (δ C = -27·1‰; δ N = 1·0‰). Juvenile M. liza exhibited a relatively fast R , with a half-life (t ) of only 16 and 14 days for δ C and δ N respectively and a nearly complete isotopic turnover (t ) of 68 and 60 days for δ C and δ N.

Contrasting energy pathways suggest differing susceptibility of pelagic fishes to an invasive ecosystem engineer in a large lake system

“…The invertebrate samples were divided into Early Season (May-July) and Late Season (August-October) because zooplankton isotopic turnover is a few weeks (Emery et al, 2015) -zooplankton tissues reflect consumption from 1 to 2 weeks before collection. Isotopic turnover for juvenile fish, however, is from 1 to 3 months (Oliveira et al, 2017;Hernández-Urcera et al, 2022), and this time lag between consumption and consumer isotopic assimilation must be considered in the models for more reliable results (Vander Zanden and Rasmussen, 2001;Hussey et al, 2014;Lanari et al, 2021;Possamai et al, 2021).…”

Trophic niches and diet shifts of juvenile mullet species coexisting in marine and estuarine habitats

“…This anaesthetic was used because it does not significantly alter stable isotopic composition (Nahon et al, 2017). Only the individuals collected in March were used in the SIA because their isotopic turnover reflects food assimilation in the prior two months of sampling (Oliveira et al, 2017) and thus the time that both species co-occur in the study system.…”

“…Models were run with uninformative priors. The trophic enrichment factor (TEF) values used were 2.1 ± 0.7 for carbon and 3.8 ± 0.4 for nitrogen, estimated specifically for juvenile mullet M. liza through controlled diet experiments (Oliveira et al, 2017). In the absence of similar experimental data for its congeneric species, the same TEF values for M. curema were applied in the Bayesian mixing models.…”

“…Therefore, it is reasonable to suggest that the juvenile mullets found in the surf-zone with isotopic composition distinct from local autotrophic sources are oceanic-derived individuals who recently recruited into the surfzone. As newly arrived individuals, they would not have enough time (∼2 months according to Oliveira et al, 2017) to achieve isotopic equilibrium with local food sources, and still reflect isotopically their original oceanic habitat.…”

“…The SCA is a higher resolution snapshot of what was recently (hours to days) consumed, while the SIA provides time-integrated (weeks to months; Oliveira et al, 2017) data reflecting dietary items assimilated in consumer tissues according to the isotopic turnover time of each particular tissue type and metabolic pathway (Hesslein et al, 1993;Mont'Alverne et al, 2016). The isotopic approach has an advantage over stomach content analysis in estimating the trophic niche overlap because it reflects assimilated food sources over a wider time window of feeding activity, which is particularly relevant considering the marked spatiotemporal variability in the availability of microalgae in the estuary (Haraguchi et al, 2015;Mendes et al, 2016).…”