Nitrogen isotope fractionation of amino acids from a controlled study on the green turtle (Chelonia mydas): expanding beyond Glx/Phe for trophic position

Lemons, Garrett E.; Lewison, Rebecca L.; Seminoff, Jeffrey A.; Coppenrath, Christina M.; Popp, Brian N.

doi:10.1007/s00227-020-03745-3

Cited by 12 publications

(12 citation statements)

References 33 publications

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“…The TDF value from analysis of the difference between Glu and Phe throughout the food web is lower in this study than the most often applied canonical value (4.9‰ compared to 7.6‰; Chikaraishi, et al 2009) as has been previously observed in multiple studies , Lemons, et al 2020, Hebert, et al 2016, Nuche-Pascual, et al 2021.…”

Section: Discussionmentioning

confidence: 48%

Compound specific stable isotope analysis of amino acid nitrogen reveals detrital support of microphytobenthos in the Dutch Wadden Sea benthic food web

Riekenberg

Heide

Holthhuijsen

et al. 2022

Preprint

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The Wadden Sea is the world's largest intertidal ecosystem and provides vital food resources for a large number of migratory bird and fish species during seasonal stopovers. Previous work using bulk stable isotope analysis of carbon found that microphytobenthos was the dominant resource use fueling the food web with particulate organic matter making up the remainder. However, this work was unable to account for the trophic structure of the food web or the considerable increase in δ15N values of bulk tissue throughout the benthic food web occurring in the Eastern regions of the Dutch Wadden Sea. Here, we combine compound specific and bulk analytical stable isotope techniques to further resolve the trophic structure and resource use throughout the benthic food web in the Wadden Sea. Analysis of δ15N for trophic and source amino acids allowed for better identification of trophic relationships due to the integration of underlying variation in the nitrogen resources supporting the food web. Baseline integrated trophic position estimates using glutamic acid (Glu) and phenylalanine (Phe) allow for disentanglement of baseline variations in underlying δ15N sources supporting the ecosystem and trophic shifts resulting from changes in ecological relationships. Through this application we further confirmed dominant ecosystem support by microphytobenthos derived resources, although to a lesser extent than previously estimated. In addition to phytoplankton derived particulate organic matter and microphytobenthos supported from nutrients from the overlying water column there appears to be an additional resource supporting the benthic community. From the stable isotope mixing models, a subset of species appears to focus on microphytobenthos supported off recycled (porewater) N and/or detrital organic matter mainly driven by increased phenylalanine δ15N values. This additional resource within microphytobenthos may play a role in subsidizing the exceptional benthic productivity observed within the Wadden Sea ecosystem and reflect division in microphytobenthos support along green (herbivory) and brown (recycled/detrital) food web pathways.

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Section: Discussionmentioning

confidence: 48%

Compound specific stable isotope analysis of amino acid nitrogen reveals detrital support of microphytobenthos in the Dutch Wadden Sea benthic food web

Riekenberg

Heide

Holthhuijsen

et al. 2022

Preprint

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“…where the trophic (Trp)/source (Src) AAs were glutamic acid-glutamine (δ 15 N Glx )/phenylalanine (δ 15 N Phe ) in skin of local green turtles, the β value was based on the primary producers (i.e., seagrass and/or marine macroalgae) present at that area, and TDF was calculated specifically for east Pacific green turtles via captive study. Calculations of TP AA used a β algae value of 3.4 AE 0.9 (Chikaraishi et al 2009) or a β seagrass value of -8.4 AE 0.06 (a proxy derived from terrestrial C 3 angiosperms; Chikaraishi et al 2010), and a TDF of 3.97 AE 0.64 (Lemons et al 2020). Marine algae were present at all sites for which AA data were available, and thus, TP AA was calculated for all these sites using β algae .…”

Section: Calculation Of Green Turtle Trophic Positionmentioning

confidence: 99%

“…S5, see also Ohkouchi et al [2017], Eq. 11) based on the equation: Green turtle TP has also been calculated using the trophic/source AA combination of Serine (δ 15 N Ser )/Lysine (δ 15 N Lys ) (Lemons et al 2020); however, this is not possible here because the β algae based on available δ 15 N Ser and δ 15 N Lys data is too imprecise (-0.9 AE 4.0, n = 13) to yield defensible TP estimates (see Montoya 2002, McCarthy et al 2013). Combinations of multiple trophic and source AAs have also been used to determine TP (Décima et al 2013, Bradley et al 2015, Nielsen et al 2015), but we were unable to apply this technique because it requires data on AAs that were not detected on chromatograms for all turtles in our analyses (e.g., Ala, Iso, Val, Met).…”

Section: Calculation Of Green Turtle Trophic Positionmentioning

confidence: 99%

“…The marine proportion of diet (ƒ algae ) was assumed to be 0 for TP seagrass and 1 for TP algae ; ƒ algae values used in TP mixed calculations were based on empirical diet data at each site; for the site that that lacked diet data (San Diego Bay), ƒ algae from the nearest neighboring site (Magdalena Bay) was used, assuming similar habitats and green turtle diets. The TDF used for Glx-Phe for skin was 3.97 AE 0.64 based on a study of green turtles (Lemons et al 2020). ß seagrass for these calculations was -8.4 AE 0.06 (C 3 plants, Chikaraishi et al 2010) and ß macroalgae was 3.4 AE 0.9 (Chikaraishi et al 2009).…”

Section: Spatial Variability In Bulk Skin δ 15 N Valuesmentioning

confidence: 99%

“…2), the TP AA and TP AA-mixed approaches (Eqs. 3, 4) relied on a TDF Glx-Phe derived for captive green turtles raised on a diet that included high-protein pellets (Lemons et al 2020). Future efforts should be made to characterize TDF Glx-Phe for green turtles raised on a natural diet.…”

Section: Green Turtle Trophic Position (Tp)mentioning

confidence: 99%

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Large‐scale patterns of green turtle trophic ecology in the eastern Pacific Ocean

Seminoff

Komoroske

Amorocho³

et al. 2021

Ecosphere

Self Cite

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Trophic position and niche width are fundamental components of a species' ecology, reflecting resource use, and influencing key demographic parameters such as somatic growth, maturation, and survival. Concepts about a species' trophic niche space have important implications for local management and habitat protection, and can shed light about resilience to changing climate for species occurring over broad spatial scales. For elusive marine animals such as sea turtles, trophic niche is challenging to study, and researchers often rely on other metrics, such as isotopic niche, as a proxy. Here, stable isotope analysis (δ 13 C and δ 15 N values) was conducted on bulk skin tissue of 718 green turtles (Chelonia mydas) distributed among 16 foraging areas in the eastern Pacific from the USA to Chile, a range spanning~10,000 km. Compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) was applied to 21 turtles among seven sites. Isotopic niche space was determined via Bayesian ellipse area (BEA) and convex hull area (CHA) analyses of bulk isotope values, which were also used along with amino acid δ 15 N values to determine trophic position (TP). Substantial variability in bulk tissue δ 13 C and δ 15 N values was found within and among sites, and amino acid δ 15 N values confirmed this was largely due to spatial differences in baseline nitrogen isotopic compositions, but also to a lesser extent from TP differences among the green turtle v www.esajournals.org 1 June 2021 v Volume 12(6) v Article e03479 foraging populations. Isotope niche space varied among sites, influenced by the diversity of prey types and relative input of terrestrial-vs. marine-derived nutrients; BEAs were the most suitable measurement of isotopic niche space due to the larger influence of outlying values with the CHA approach. Amino acid isotope-derived TP estimates that accounted for local habitat conditions (e.g., mixed seagrass/macroalgae diet) performed the best among several approaches; TP ranged from 2.3 to 3.6, which indicates an omnivorous diet for most populations. In addition to providing additional spatial resolution for δ 13 C and δ 15 N isoscapes in the eastern Pacific, especially in coastal habitats, this study further establishes CSIA-AA as an effective tool to study the trophic ecology of sea turtles across a variety of food webs and habitats.

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Shortened food chain length in a fished versus unfished coral reef

Young,

McCauley,

Micheli

et al. 2024

Ecological Applications

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Direct exploitation through fishing is driving dramatic declines of wildlife populations in ocean environments, particularly for predatory and large‐bodied taxa. Despite wide recognition of this pattern and well‐established consequences of such trophic downgrading on ecosystem function, there have been few empirical studies examining the effects of fishing on whole system trophic architecture. Understanding these kinds of structural impacts is especially important in coral reef ecosystems—often heavily fished and facing multiple stressors. Given the often high dietary flexibility and numerous functional redundancies in diverse ecosystems such as coral reefs, it is important to establish whether web architecture is strongly impacted by fishing pressure or whether it might be resilient, at least to moderate‐intensity pressure. To examine this question, we used a combination of bulk and compound‐specific stable isotope analyses measured across a range of predatory and low‐trophic‐level consumers between two coral reef ecosystems that differed with respect to fishing pressure but otherwise remained largely similar. We found that even in a high‐diversity system with relatively modest fishing pressure, there were strong reductions in the trophic position (TP) of the three highest TP consumers examined in the fished system but no effects on the TP of lower‐level consumers. We saw no evidence that this shortening of the affected food webs was being driven by changes in basal resource consumption, for example, through changes in the spatial location of foraging by consumers. Instead, this likely reflected internal changes in food web architecture, suggesting that even in diverse systems and with relatively modest pressure, human harvest causes significant compressions in food chain length. This observed shortening of these food webs may have many important emergent ecological consequences for the functioning of ecosystems impacted by fishing or hunting. Such important structural shifts may be widespread but unnoticed by traditional surveys. This insight may also be useful for applied ecosystem managers grappling with choices about the relative importance of protection for remote and pristine areas and the value of strict no‐take areas to protect not just the raw constituents of systems affected by fishing and hunting but also the health and functionality of whole systems.

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Nitrogen isotope fractionation of amino acids from a controlled study on the green turtle (Chelonia mydas): expanding beyond Glx/Phe for trophic position

Cited by 12 publications

References 33 publications

Compound specific stable isotope analysis of amino acid nitrogen reveals detrital support of microphytobenthos in the Dutch Wadden Sea benthic food web

Compound specific stable isotope analysis of amino acid nitrogen reveals detrital support of microphytobenthos in the Dutch Wadden Sea benthic food web

Large‐scale patterns of green turtle trophic ecology in the eastern Pacific Ocean

Shortened food chain length in a fished versus unfished coral reef

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