Was that my meal? Uncertainty from source sampling period in diet reconstruction based on stable isotopes in a syngnathid fish

Abstract

Stable isotopes can be used to reconstruct diet in fishes, an approach that is particularly useful in threatened or endangered species where lethal sampling needs to be avoided To apply this method stable isotopes need to be measured both in the consumers and dietary sources As turnover rates may largely differ across tissues, the reconstruction should consider the uncertainty associated with sampling timing for both consumers and dietary sources. The present study investigated for the first time the application of a time lag for the estimation of the trophic position and the dietary regime in the greater pipefish Syngnathus acus (Family Syngnathidae). For that, two isotopic (δ13C and δ15N) data sets from dorsal fin-clipped tissues were used, including values in potential sources sampled (a) concomitantly with consumers (Unshifted approach) or (b) in the season sampled preceding consumer sampling (Shifted approach). The results attained indicate that the trophic position of the species was not affected (< 0.6% change) by shifting when analyzed for the annual dataset (global assessment). However, the trophic level estimated in the shifted treatment was ca. 6% higher than in the unshifted approach when the analysis was performed using a seasonal dataset (seasonal assessment including exclusively specimens collected in summer). Regarding the reconstruction of the dietary regime and in comparison to the unshifted approach, the results attained with shifted sampling revealed a higher preference for amphipods (43.7%), isopods (19.5%) and mysidaceans (12.1%), and a reduction in the reconstructed abundance for harpacticoid copepods (5.1%). These findings were similar to those attained for specimens and food web components collected in the same sampling period (seasonal dataset), both in females and males. This study demonstrates (1) the variability of estimates in the reconstruction of diet regimes depending on the data time shifting applied, and (2) the importance of considering adequate time lags in the assessment for syngnathid fishes.

Trophic Niches of Two Congeneric Pipefishes in the Aegean Sea (Bargilya Wetland, Turkey), Based on Stable Isotope Analyses

“…Specimens of S. abaster from the western Mediterranean Stagnone di Marsala mainly fed on Mysidacea and Isopoda [37]. The dietary regime of S. acus from Cíes Archipelago seemed to prey primarily upon amphipods with varying proportions of carideans, isopods, copepods and mysidaceans [34,83]. However, Gurkan and Taskavak [84] reported the importance of cladocerans in the diet of the greater pipefish in the Turkish Aegean Sea, whereas Gurkan et al [40] pointed out the preference for amphipods and copepods.…”

Regional assessment of important biological indices in the population of red cornetfish (Fistularia petimba Lacepède, 1803) along the eastern Mediterranean coasts of Türkiye

“…Stomach morphology also plays a significant role in the trophic relationships of species. Different methods, including the analysis of stomach and intestinal contents, are used to determine feeding patterns and trophic positions in animals (Planas, 2022). The visceral index serves as an indicator of the effects of carbohydrates and proteins in the fish's diet on their internal organs (Gurkan et al, 2021).…”