Experimental evaluation of ontogenetic diet transitions in summer flounder (Paralichthys dentatus), using stable isotopes as diet tracers

Abstract

We examined the rate of isotopic change of nitrogen (N) and carbon (C) and isotopic fractionation at two temperatures during several ontogenetic diet transitions in summer flounder (Paralichthys dentatus). We examined prefeeding larvae as they metabolize the maternal source of nutrition and evaluated three diet transitions in the early life stages of this species: (i) yolk dependency to first feeding on zooplankton, (ii) one zooplankton (rotifers) to another (Artemia), and (iii) zooplanktivory to piscivory. We used experimental results and simulations to contrast time- versus growth-based models for estimating parameters of isotopic change and fractionation. All rates of isotopic change were lowest for the transition between zooplanktivory and piscivory, most rapid for the transition from yolk dependency to first feeding, and generally lower at cooler temperatures. Estimates of fractionation were greater for N (2.8‰–3.8‰) than for C (0.23‰–0.91‰) but appeared to be unaffected by water temperature or fish life stage. Simulation results suggested that parameter estimates of isotopic change and fractionation may be compromised when growth rates are low unless sampling design is modified to address slow growth rates. We conclude that sampling strategy and the model used can influence the accuracy and precision of estimates of isotopic change and fractionation.

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…Heady and Moore (2013) revealed that catabolism contributed more to 15 N turnover in tissues with faster turnover rates, contributing 68% for fin compared to 0.7% for scales. Experimental design, especially the temperature used, can also significantly impact turnover rates, with higher water temperatures reducing the half-lives of the carbon stable isotope of muscle in similar sized fish (Bosley et al, 2002;Witting et al, 2004). Caution must also be applied when the contributions of metabolism to turnover are estimated and represented by a metabolic constant, as this constant covers all non-growth processes that contribute to turnover, including inter-tissue recycling of nutrients, preferential isotopic routing and amino-acid effects, and these processes may operate differently during isotopic uptake and elimination (MacNeil et al, 2006).…”

“…Hence, the half-lives estimated with this growth-based model were expressed as an x-fold mass increase. The fractions of new tissue derived from growth (D g ) and from metabolism (D m ) were calculated at the midpoint between the old and new isotopic values (Witting et al, 2004):…”

“…Moreover, the determination of the turnover rates of wild consumers can be problematic, as they tend to assimilate a range of prey items that vary temporally and spatially in isotopic content (Perga & Gerdeaux, 2005). Consumer species are also unlikely to feed on the same proportions of prey items on a daily basis and consumer isotopic turnover rates are also influenced by a number of other factors, including temperature fluctuations and life-history events (Bearhop et al, 2002;Bosley et al, 2002;Witting et al, 2004). Turnover rates also differ between fish species and between different tissues of individual species (e.g.…”

Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues

“…Therefore, turnover rates can be well predicted by a time-based model. Relative to the time-based model, the growth-based model may be more suitable in experimental conditions of variable temperatures and growth rates because any variability in growth rates is inherently accounted for by the relative growth variable W R (Witting et al 2004). Bosley et al (2002) showed that c did not vary greatly between temperature treatments despite changes in fish growth rates.…”

δ15N and δ13C elucidation of size-structured food webs in a Western Arabian Sea demersal trawl assemblage

“…However, given the comparatively slow turnover observed in the fish muscle of juveniles < 30% L max (Hesslein et al 1993, Sweeting et al 2005) and the fact that turnover decelerates rapidly with age as reduction in growth-based dilution diminishes (Witting et al 2004), such variation is unlikely to strongly influence analysis of fish at 55 to 80% L max .…”