Tissue-specific Isotopic Incorporation Turnover Rates and Trophic Discrimination Factors in the Freshwater Shrimp Macrobrachium borellii (Crustacea: Decapoda: Palaemonidae)

• Published in: Zoological Studies 2021-07, Vol.60, p.1-11
• Main Authors: Viozzi, María Florencia, Del Rio, Carlos Martínez, Williner, Verónica
• Format: Article
• Language: English
• ISSN: 1021-5506; 1810-522X
• DOI: 10.6620/ZS.2021.60-32

The interpretation of isotopic data in ecology requires knowledge about two factors: turnover rate and the trophic discrimination factor, which have not been well described in freshwater shrimps. We performed a 142-day diet shift experiment on 174 individuals of the omnivorous shrimp Macrobrachium borellii, measured their growth, and temporally serially sampled muscle and hepatopancreas tissue to quantify carbon and nitrogen incorporation rates and isotope discrimination factors. Shrimps were fed with artificial diets (δ^(13)C = (-26.1 per mille), δ^(15)N= (2.1 per mille)) for 45 days in attempt to standardize the shrimps' initial δ^(13)C and δ^(15)N values for subsequent experiments. Shrimps were then fed with another artificial diet (δ^(13)C = (-16.1 per mille), δ^(15)N = (15.8 per mille)) and the change in δ^(13)C and δ^(15)N was observed for a period of 97 days. The trophic discrimination factor (Δ) for δ^(13)C was significantly higher in hepatopancreas ((0.7 ± 0.36 per mille)) than in muscle ((-0.1 ± 0.83 per mille)); however, the opposite was the case for δ^(15)N ((1.7 ± 0.43 per mille) and (3.6 ± 0.42 per mille), respectively). In the hepatopancreas the mean residence time (τ) of ^(13)C was 26.3 ± 4.3 days compared to a residence time of 16.6 ± 5.51 days for δ^(15)N, whereas the τ in muscle was 75.8 ± 25 days for δ^(13)C and 40 ± 25 days for δ^(15)N. The rate of incorporation of carbon into muscle was higher than that predicted by allometric equations relating isotopic incorporation rate to body mass that was developed previously for invertebrates. Our results support ranges of traditional trophic discrimination factor values observed in muscles samples of different taxa (Δ^(15)N around (3-3.5 per mille) and Δ^(13)C around (0-1 per mille)), but our work provides evidence that these traditionally used values may vary in other tissues, as we found that in the hepatopancreas Δ^(15)N is around (1.7 per mille).