Stable isotope analysis indicates resource partitioning and trophic niche overlap in larvae of four tuna species in the Gulf of Mexico

Abstract

In this study we assessed the trophic ecology of bluefin tuna Thunnus thynnus larvae from the Gulf of Mexico, together with the co-occurring larvae of blackfin tuna T. atlanticus, bullet tuna Auxis rochei, and skipjack Katsuwonus pelamis, using both bulk-tissue stable isotope analysis (SIA bulk) and compound-specific analysis of amino acids (CSIA AA). Bulk nitrogen (δ 15 N bulk) and carbon (δ 13 C bulk) values differed significantly among species, suggesting partitioning of resources due to an adaptive process allowing these tunas to share the ecosystem's trophic resources during this early life period. K. pelamis had the largest isotopic niche width, likely due to piscivorous feeding at an earlier age compared to the other species, with an isotopic niche overlap of 17.5% with T. thynnus, 15.8% with T. atlanticus, and 31.2% with A. rochei. This trophic overlap suggests a mix of competition and trophic differentiation among these 4 species of tuna larvae. Higher nitrogen isotopic signatures in preflexion versus postflexion larvae of T. thynnus measured using both SIA bulk and CSIA AA indicate maternal isotopic transmission, as well as 'capital breeder'-like characteristics. In contrast, the nitrogen isotopic ratios of the other 3 species were similar between ontogenetic stages. These observations suggest different breeding strategies within the study area for T. atlanticus, K. pelamis, and A. rochei compared to T. thynnus. No significant differences were observed among the 4 species' trophic positions (TPs) estimated by CSIA AA , whereas a higher TP was observed for T. thynnus by SIA bulk. These differences in TP estimation may be attributed to discrepancies in baseline estimates.

Amino acid nitrogen and carbon isotope data: Potential and implications for ecological studies

“…SIR in compound level is more tightly associated with the exact biomolecules (e.g., AAs), whereas bulk SIR of whole tissue or total protein depends on inter‐molecular isotope differences and the molecular quantities. AA‐SIR values reflect more sensitive physiological responses of consumers to environmental change within local habitats as well as broader geographic scales (Cherel et al, 2019 ; Choi & Shin, 2021 ; Laiz‐Carrión et al, 2019 ; Le‐Alvarado et al, 2021 ; McMahon et al, 2016 ; Richards et al, 2020 ; Smith et al, 2020 ; Zupcic‐Moore et al, 2017 ). In fact, AA‐SIR values are controlled by environmental characteristics such as the availability of inorganic substrates, differences in the baseline levels of isotopes, and the physicochemical parameters of local habitats (Decima et al, 2017 ; Gutierrez‐Rodriguez et al, 2014 ), or some combination of the three in natural environments (Magozzi et al, 2017 , 2021 ; McMahon et al, 2013 ).…”

Trade-offs between risks of predation and starvation in larvae make the shelf break an optimal spawning location for Atlantic Bluefin tuna

“…The onset of piscivory in larval tuna is closely timed with the transition from flexion to postflexion stage (~2 weeks post hatch)(Llopiz and Hobday, 2015; Blanco et al , 2019; Uriarte et al , 2019; Laiz-Carrión et al , 2019). Individuals are tracked for three weeks, fully encompassing the period when larval ABT are obligate planktivores.…”

Errors associated with compound‐specific δ15N analysis of amino acids in preserved fish samples purified by high‐pressure liquid chromatography

“…The superior 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 9 precision and accuracy of this method are particularly suitable for studies attempting to resolve fine-scale variability in N sources and TPs. Among primary or secondary consumers in marine pelagic systems, for instance, temporal and spatial variability in TP is usually on the order of AE 0.4 TP (Hannides et al 2009;Choy et al 2012Choy et al , 2015Décima et al 2013;Miyachi et al 2015;Bradley et al 2016;Laiz-Carrión et al 2019). Even small shifts in TP can be associated with significant food web disruptions and represent considerable changes in energy transfer to higher level consumers (Vander Zanden et al 1999).…”