Trophic Enrichment Factor Research Articles

Trophic ecology of mesopelagic fishes in the northern and southern Benguela Upwelling Systems revealed through stable isotope patterns

Mesopelagic fishes are important components of marine food webs as trophic links between primary consumers and higher trophic levels, but their trophic ecology is poorly understood. We used stable isotopes (δ13C and δ15N) to compare the trophic position, trophic enrichment factor, and isotopic niche among feeding guilds of mesopelagic fishes (including myctophids, stomiids) during different seasons in the northern and southern Benguela Upwelling Systems. These subsystems are influenced by differing water masses with various physical and biological properties, which can lead to changes in the marine food web. We aimed to determine if and how the trophic ecology of mesopelagic fishes differs between seasons and subsystems. When separating fishes into guilds based on dietary preferences (zooplanktivores vs. piscivores) and migration patterns (migrating vs. non-migrating), the trophic position was highest during winter in the south for non-migrating piscivores (4.5), but the trophic positions of piscivores (3.2-4.4) were not always higher than those of zooplanktivores (3.1-4.5). This may indicate different isotopic enrichment between species or a very generalist diet from zooplanktivores such as myctophids and their prey. Trophic enrichment factors for δ15N among guilds ranged from 3.8 to 7.5‰ between the baseline and zooplanktivores and from -0.8 to 1.6‰ between zooplanktivores and piscivores. Previously, mesopelagic fishes have been incorporated into food web models in the Benguela Upwelling Systems, but only as a single entity. Elucidating the complex seasonal and regional trophodynamics of various mesopelagic feeding guilds may contribute to more accurate assessments of trophic transfer efficiencies and higher-resolution models in these systems.

Species-specific trophic enrichment factor of stable nitrogen and carbon isotopes in fish otolith organic matter

Context Although stable carbon (δ13C) and nitrogen (δ15N) isotopes are widely used to study feeding ecology, the use of these isotopes in otolith organic matter to assess the diet of fishes is rarely investigated. Aim This study evaluated the relationship of δ13C and δ15N values among muscle, otolith organic matter and diet. The samples were analysed using an elemental analyzer connected to isotope-ratio mass spectrometry. Key results The δ15N values were highest in muscle followed by otoliths, diet and plankton, although no significant difference in δ15N values was found between the otolith and diet for most of the samples. The fish collected from water reservoirs showed similar δ13C values between otolith and muscle, both of which were higher than the isotopic values of the fish diet. However, the farmed fishes showed small but significant difference in the δ13C values between muscle and otolith, which reflects diet change or commercial diet containing a mixture of different food items. Conclusion Otolith δ15N value can provide information about fish diet and the otolith δ13C value can act as a good proxy of muscle δ13C composition in fish species. Implications Otolith δ15N and δ13C values can faithfully reflect the trophic position and feeding behaviours of fish.

Comparison Between Trophic Positions in the Barents Sea Estimated From Stable Isotope Data and a Mass Balance Model

The trophic position concept is central in system ecology, and in this study, trophic position (TP) estimates from stable-isotopes and an Ecopath mass-balance food web model for the Barents Sea were compared. Two alternative models for estimating TP from stable isotopes, with fixed or scaled trophic fractionation were applied. The mass-balance model was parametrized and balanced for year 2000, was comprised of 108 functional groups (Gs), and was based on biomass and diet data largely based on predator stomach data. Literature search for the Barents Sea Large Marine Ecosystem revealed 93 sources with stable isotope data (δ15N values) for 83 FGs, and 25 of the publications had trophic position estimated from nitrogen stable isotopes. Trophic positions estimated from the mass-balance model ranged to 5.1 TP and were highly correlated with group mean δ15N values, and also highly correlated with the original literature estimates of trophic positions from stable isotopes. On average, TP from the mass-balance model was 0.1 TP higher than the original literature TP estimates (TPSIR) from stable isotopes. A trophic enrichment factor (TEF) was estimated assuming fixed fractionation and minimizing differences between trophic positions from Ecopath and TP predicted from δ15N values assuming a baseline value for δ15N calculated for pelagic particulate organic matter at a baseline TP of 1.0. The estimated TEF of 3.0‰ was lower than the most commonly used TEF of 3.4 and 3.8‰ in the literature. The pelagic whales and pelagic invertebrates functional groups tended to have higher trophic positions from Ecopath than from stable isotopes while benthic invertebrate functional groups tended to show an opposite pattern. Trophic positions calculated using the scaled trophic fractionation approach resulted in lower TP than from Ecopath for intermediate TPs and also a larger TP range in the BS. It is concluded that TPs estimated from δ15N values using a linear model compared better to the Ecopath model than the TPs from scaled fractionation approach.

Phytoplankton Fuel Fish Food Webs in a Low-Turbidity Temperate Coastal Embayment: A Stable Isotope Approach

Trophic contributions of diverse OM sources to estuarine and coastal food webs differ substantially across systems around the world, particularly for nekton (fish, cephalopods, and crustaceans), which utilize basal resources from multiple sources over space and time because of their mobility and feeding behaviors at multiple trophic levels. We investigated the contributions of putative OM sources to fish food webs and assessed the spatiotemporal patterns, structures, and trophic connectivity in fish food webs across four seasons from three closely spaced (10–15 km) sites: an estuarine channel (EC), a deep bay (DB), and an offshore (OS) region in Gwangyang Bay, a high-productivity, low-turbidity estuarine embayment off the Republic of Korea. While nearly all previous studies have focused on few representative species, we examined δ13C and δ15N values of whole nekton communities along with dominant benthic macro-invertebrates, zooplankton, and their putative primary food sources. The δ13C and δ15N values coupled with MixSIAR, a Bayesian mixing model, revealed that these communities utilized multiple primary producers, but phytoplankton comprised the primary trophic contributor (46.6–69.1%). Microphytobenthos (15.8–20.4%) and the seagrass Zostera marina (8.6–19.8%) made substantial contributions, but the role of river-borne terrestrial organic matter was negligible. Spatially different species composition and stable isotope values, but higher utilization of coastal phytoplankton by estuarine fish, indicated disparate food webs structures between the EC and DB/OS coastal areas, with considerable trophic connectivity. Greater overlaps in fish and cephalopod isotopic niches than among other consumers and a higher estimated carbon trophic enrichment factor for EC nekton confirmed feeding migration-mediated biological transport of coastal OM sources to the estuary. Further, the seasonally consistent structures and resource utilization patterns indicate that fish food webs are resilient to changes at lower trophic levels. Our results contrast with those for other highly turbid coastal systems depending highly on diversified basal sources, including exported terrestrial and wetland detritus alongside autochthonous phytoplankton. Finally, this study provides a novel perspective on the role of OM sources in such low turbidity and highly productive coastal embayments and enhances our understanding of marine ecosystems.

Carbon supplementation promotes assimilation of aquaculture waste by the sea cucumber Holothuria scabra: Evidence from stable isotope analysis

Cultivating high-value deposit feeders such as sea cucumbers on solid waste from intensive aquaculture is an innovative approach to turn potential nutrient pollution into a resource. Carbon supplementation to increase the carbon to nitrogen ratio (C:N) of the nitrogen-rich aquaculture waste has been demonstrated to support higher deposit feeder biomass, but commercially viable carbon sources remain to be tested. This experiment investigated the performance of laboratory grade cellulose and bagasse, an agricultural waste product, to improve growth and nutrient utilization from milkfish aquaculture waste in juveniles of the sea cucumber Holothuria scabra. Supplementation with bagasse supported a significantly higher final biomass density (205.71 ± 11.08 g m−2, mean ± SE) than waste without carbon supplementation (p = 0.027). For the first time, a species-specific trophic enrichment factor (Δ13Corg) was applied in stable isotope analysis of feed sources by H. scabra (Δ13Corg of 2.56 ± 0.96‰ (mean ± SD) for the internal organs and 4.31 ± 0.96‰ for the body wall). Results indicated that sea cucumbers were able to assimilate carbon directly from the cellulose. Bagasse supported higher uptake of carbon from aquaculture waste, thus identifying it as a viable resource to improve bioremediation by deposit feeding sea cucumbers in integrated aquaculture. While illustrating the importance of nutrient balances for bioremediation, questions remain about the roles of direct feeding by deposit feeders vs. the decomposition by microbial communities.

Experimentally derived trophic enrichment and discrimination factors for Chinook salmon, Oncorhynchus tshawytscha.

Stable isotope analysis (SIA) can provide important insights into food web structure and is a widely used tool in ecological conservation and management. It has recently been augmented by compound-specific stable isotope analysis of amino acids (CSIA-AA), an innovation that can provide greater precision when analyzing trophic level and food web connectivity. The utility of SIA rests on confidence in its constituent parameters such as the trophic enrichment factor (TEF). There is increasing emphasis on the need to experimentally derive species and tissue specific TEFs for studies utilizing SIA. Chinook salmon, Oncorhynchus tshawytscha, is a species with high potential for study using SIA due to the difficulty in observing its ecology during its marine phase and the significance of the conservation consequences of recent population declines. Bulk and amino acid-specific TEFs were determined for juvenile and adult Chinook salmon fed specific diets. Three controlled feeding studies were performed: adult salmon were fed a biofeed, juvenile salmon were fed a biofeed, and juvenile salmon were fed krill. Bulk and compound-specific stable isotope data were collected from diet samples and from salmon muscle tissue after a minimum of 8weeks of controlled feeding. Bulk isotope signatures were measured using EA-IRMS and CSIA-AA signatures using GC/C-IRMS, allowing the TEFs to be calculated. The bulk isotope TEFs were higher than those predicted for similar marine organisms and averaged 3.5‰ for ∆15 N and 1.3‰ for ∆13 C. The TEFs derived for nitrogen isotopes of amino acids were in line with expectations for this approach: the mean value for ∆15 NGlu - ∆15 NPhe was 7.06‰ and, using a multi-AA approach, the value for ∆15 NTrophic - ∆15 NSource was 6.67‰. For carbon isotopes of amino acids, the derived TEFs of Iso, Leu and Phe were near 0‰, as was that of Met, supporting their use of as source amino acids in future CSIA studies. This study presents Chinook salmon-specific TEFs for bulk and amino acid SIA. It supports the application of future research applying SIA to the study of Chinook salmon and validates previous research on species-specific TEFs.

Body size and stable isotope composition of zooplankton in the western tropical Atlantic

Abstract Size-based approaches are paramount tools for the study of marine food webs. Here, we investigated the relationship between zooplankton body size, stable isotope composition and trophic level (TL) along a large-scale onshore-offshore gradient in the western tropical Atlantic. Samples were obtained on the Brazilian continental shelf, slope and in oceanic waters (off Fernando de Noronha archipelago and Rocas Atoll) in September and October 2015. Zooplankton was sieved into five size fractions. Zooplankton was dominated by copepods, except for the largest (>2000 μm) size fraction, that showed a high biovolume of chaetognaths, decapods, and fish larvae. Maximum zooplankton abundance and biovolume was found at the continental slope. POM showed consistently lower δ13C than zooplankton, indicating a selective use of 13C-rich primary food sources by zooplankton. Particulate organic matter (POM) was more 13C-enriched in shelf areas (average: −22.8, −23.6 and − 24.3‰ at the shelf, slope and oceanic islands, respectively), probably due to the higher abundance of diatoms nearshore. POM had δ15N values between 2.5 and 6.9‰ (average: 4.0, 4.9 and 4.2‰ at the shelf, slope and oceanic islands, respectively). Zooplankton δ15N and TL increased with body size. The δ15N of the 200–500 μm size fraction was used as baseline for TL estimation. Oceanic areas (average baseline δ15N = 5.8‰ ± 0.52, n = 14) showed a higher baseline δ15N than the shelf (average = 3.9‰ ± 0.69, n = 9) and the slope areas (average = 3.1‰ ± 0.93, n = 9). In spite of differing baselines, the δ15N data produced a consistent pattern of log-linear increase in TL with increasing size, in all areas. The choice of input trophic enrichment factor (TEF) values only slightly changed the log10 (body size) vs TL slopes, but this choice had a considerable effect on the estimates of predator/prey size ratio (PPSR) and predator/prey mass ratio (PPMR). Using a TEF above 2.3 leads to unrealistic PPSR and PPMR estimates. Overall average slope was 0.59 ± 0.08 TL μm−1 with TEF = 2.3 and 0.42 ± 0.07 TL μm−1 with TEF = 3.2.

Food web reconstruction through isotopic compositions of fossil faeces: Insights into the ecology of a late Barremian freshwater ecosystem (Las Hoyas, Cuenca, Spain)

A total of 54 coprolites with different morphologies from the Konservat-Lagerstätte of Las Hoyas (upper Barremian, Cuenca, Spain) were analysed for stable isotopes (δ15N and δ13Corg) to examine the food-web structure of this ancient wetland. The Las Hoyas wetland exhibited wetter and drier periods that indicated water table oscillations. Differences in the δ15N values of coprolites collected from wetter and drier facies were probably due to different baseline δ15N values during the dry periods (higher) compared to those of the wetter periods. The δ13Corg values indicated that aquatic food resources were the most commonly used by the animals from Las Hoyas. Assuming a Trophic Enrichment Factor (TEF) of + 2.5 ‰, three trophic levels were established for the coprolite association. All the specimens of circular, ellipsoidal, elongated, and rosary morphotypes fell into the same trophic level, whereas other morphotypes (cylinder, irregular, and thin lace) exhibited a wide range of δ15N values and the highest % N concentrations. The covariation between δ15N and δ13Corg values describe a wide spectrum of values across the middle and upper part of the ecosystem's food web structure, suggesting that the Las Hoyas ecosystem hosted specialist feeders and omnivorous and/or opportunistic feeders, the latter being the majority. The variation of δ15N values within the specimens of some morphotypes showed that the larger coprolites do not exhibit any correspondence between the faecal size and δ15N values.

Prey-to-fox isotopic enrichment of 34 S in bone collagen: Implications for paleoecological studies.

The trophic enrichment factor (TEF) is a parameter reflecting the difference in isotopic ratio between a consumer's tissues and diet, used in isotopic ecology and paleoecology to track dietary habits. The TEF of sulfur is believed to be low, but was, until now, only documented in a limited number of taxa. In this study we use a subfossil accumulation of bones from a red fox (Vulpes vulpes) den to verify the TEF for sulfur in fox bone collagen. Collagen was extracted from 30 samples of subfossil bones, including foxes and their prey. The δ34 S values of the bone collagen samples were measured with an elemental analyzer connected to an isotope ratio mass spectrometer. The TEF was calculated as [Δ34 S = (mean δ34 S in predator) - (mean δ34 S in prey)], using taphonomic indices to estimate the mean diet, and calculated separately for different age classes of the predator. We modeled 12 variants of TEF for different estimations of the diet composition and for three fox age classes (adult, subadult, and juvenile). The estimated TEF values range from -0.54 to +0.03‰ and are similar to TEFs known for other mammals. Absolute TEF values are nearly equal to or lower than the analytical error, which is ±0.4‰. For the first time, we present direct δ34 S data for the bone collagen of a free-living predator and its naturally selected prey. Our results indicate very low or even slightly negative TEF values for sulfur. Furthermore, according to our results, the δ34 S value should not be considered a reliable indicator of trophic position in terrestrial food webs but rather, it should be used to disentangle different food webs based on different primary producers.

Coastal complexity: Ancient human diets inferred from Bayesian stable isotope mixing models and a primate analogue.

An extensive ecological literature applies stable isotope mixing models to derive quantitative dietary reconstructions from isotope ratios of consumer tissues. While this approach works well for some organisms, it is challenging for consumers with complex, varied diets, including humans; indeed, many archaeologists have avoided the use of mixing models because uncertainties in model outputs are sufficiently large that the findings are not helpful in understanding ancient lifeways. Here, we exploit an unparalleled opportunity to evaluate the feasibility of dietary quantification in a nutritionally and isotopically complex context on the Cape Peninsula, South Africa. Delta values (δ13C and δ15N) of 213 indigenous food samples enable us to characterise four food groups: terrestrial plants, terrestrial vertebrates, marine invertebrates and marine vertebrates. A recent study of baboons that consumed marine and terrestrial foods provides insight into the relationship between such foods and consumer tissue isotopes. We use this information to refine our interpretation of δ15N and especially δ13C in bone collagen from 35 archaeological hunter-gatherers, achieving better estimates of the relative importance of marine and terrestrial foods in the diet than has hitherto been possible. Based on Bayesian stable isotope mixing model (SIMM) outputs, we infer that the trophic enrichment factor (TEF) for δ13Cbone collagen in these coastal humans is closer to +3 than +5‰. In the most 13C- and 15N-rich individuals, 65–98% of bone collagen (95% credible intervals) derived from marine foods. Conversely, in 13C and 15N-poor individuals, 7–44% of bone collagen derived from marine foods. The uncertainties discussed here highlight the need for caution when implementing SIMMs in studies of consumers with complex diets. To our knowledge, this work constitutes the most detailed and most tightly constrained study of this problem to date.

Isotopic signatures in Mytilus galloprovincialis and Ulva latuca as bioindicators for assessing discharged sewage effluent in coastal waters along Otago Peninsula, New Zealand

ABSTRACTSewage, waste organic matter from domestic and municipal wastewater, causes increased secondary productivity, eutrophication and trace metal contamination, reduced oxygen levels, and biodiversity which can lead to ecological disturbances in the natural aquatic ecosystem. The impact of sewage-derived organic matter (SDOM) on the nearshore marine ecosystem of the Otago Coast was assessed before, and 15 years after upgrade of the Dunedin sewage treatment plant. Carbon and nitrogen isotopic ratios in the tissues of sentinel organisms were used as bioindicators to elucidate the primary sources of nutrition the coastal environment. Mytilus galloprovincialis, a marine bivalve, exhibited a strong influence of SDOM from two sites in 2001. In 2015, M. galloprovincialis had a trophic enrichment factor of 3‰ (δ15N) and 1‰ (δ13C) when compared to the marine particulate organic matter (POM), suggestive of a dietary change away from the SDOM. Suspended POM collected from riverine and estuarine sources revealed other possible nitrogen sources from human-driven activities such as pastoral farming, application of organic manure and inorganic fertilisers, nitrification of ammonium from semi-urban septic tanks, and animal organic waste residues.

Phytoplankton as a principal diet for callianassid shrimp larvae in coastal waters, estimated from laboratory rearing and stable isotope analysis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 592:141-158 (2018) - DOI: https://doi.org/10.3354/meps12507 Phytoplankton as a principal diet for callianassid shrimp larvae in coastal waters, estimated from laboratory rearing and stable isotope analysis Yu Umezawa1,2,*, Akio Tamaki1, Toshikazu Suzuki1, Seiji Takeuchi1, Chikage Yoshimizu3, Ichiro Tayasu3 1Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan 2Department of Environmental Science on Biosphere, Tokyo University of Agriculture and Technology, Saiwai-cho, Fuchu, Tokyo 183-8509, Japan 3Research Institute for Humanity and Nature, Motoyama, Kamigamo, Kyoto 603-8047, Japan *Corresponding author: umezawa@me.tuat.ac.jp ABSTRACT: The field diet of meroplanktonic decapod crustacean larvae is poorly known, despite standard use of microzooplankton as food in laboratory culture. Using callianassid shrimp Nihonotrypaea harmandi larvae collected from a 65 m deep inner-shelf location off mid-western Kyushu, Japan, between June and August 2012 and 2013 and mass-reared in the laboratory, a phytoplankton-based diet through larval development (zoeae I–VI to decapodid) was demonstrated. When the pure-cultured diatom Chaetoceros gracilis was fed to zoeae, survival rate to decapodids was 3.4 to 3.9% in 26 to 40 d at 22°C, which was comparable to previous rearing results for zoeae fed microzooplankton. Trophic enrichment factors (TEFs) from stable isotope (SI) analysis of zoeal whole-body tissue in the laboratory were 2.0‰ for δ13C and 1.9‰ for δ15N. In the field water column, diatoms dominated the nano- to micro-sized plankton, accounting for 38 to 81% of the biovolume, followed by heterotrophic protists. The trophic position (TP) estimated from amino acid-specific δ15N values for the field-collected zoeae VI was 2.1 (TPGlu/Phe) or 2.7 (TPAla/Phe), suggesting that those zoeae fed on mixtures of phytoplankton and heterotrophs including protists. Bulk SI analyses were performed for particulate organic matter (POM; proxy for phytoplankton), microzooplankton (mainly calanoid copepods), and shrimp zoeae to elucidate the diet of larvae in the water column. A shift in SI from fresh to degraded POM was determined through the incubation of field-collected POM. Based on this shift during degradation and larval TEFs, phytoplankton and their sinking detritus with heterotrophic protists were estimated to be the principal diet for those larvae residing mostly below the chlorophyll maximum layer. KEY WORDS: Nihonotrypaea harmandi · Zoea · Rearing · Diatom · Isotopic trophic enrichment factor · Amino-acid-δ15N-based trophic position · Phytodetritus · Protists Full text in pdf format Supplementary material PreviousNextCite this article as: Umezawa Y, Tamaki A, Suzuki T, Takeuchi S, Yoshimizu C, Tayasu I (2018) Phytoplankton as a principal diet for callianassid shrimp larvae in coastal waters, estimated from laboratory rearing and stable isotope analysis. Mar Ecol Prog Ser 592:141-158. https://doi.org/10.3354/meps12507 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 592. Online publication date: March 29, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Collagen-to-collagen prey-predator isotopic enrichment (Δ13C, Δ15N) in terrestrial mammals - a case study of a subfossil red fox den

Trophic Enrichment Factor (TEF) is the main parameter used in isotopic trophic ecology. TEF values can be derived from specimens subjected to experimental feeding or from free-ranging specimens whose dietary behavior is well monitored, and it can be measured for different tissues of animal body. Direct collagen-to-collagen TEF is a key parameter for fossil material and needs to be well constrained in order to ascertain the reliability of the palaeodietary models. In this paper, we present isotopic results for a subfossil bone accumulation related to red fox (Vulpes vulpes) activity, discovered in an abandoned mine in Potok-Senderki (Poland). The objective was to report δ13C and δ15N collagen data for red foxes and their prey. These data were used to calculate a prey-predator collagen-to-collagen TEF and provided important information for interpreting stable isotope fractionation in terrestrial food webs. We used different taphonomic indexes to calculate the fox mean diet. The presence of juvenile and adult individuals of fox allowed us to specify the difference in isotopic enrichment according to the age class of the predator. Δ13C and Δ15N values calculated here for fox were similar to TEF values presented previously for wolf and lynx, but characterized by wider standard deviation.

Carbon, nitrogen and sulphur isotopic fractionation in captive juvenile hooded seal (Cystophora cristata): Application for diet analysis.

Intrinsic biogeochemical markers, such as stable isotope ratios of carbon, nitrogen and sulphur, are increasingly used to trace the trophic ecology of marine top predators. However, insufficient knowledge of fractionation processes in tissues continues to hamper the use of these markers. We performed a controlled feeding experiment with eight juvenile hooded seals (Cystophora cristata) that were held on a herring-based diet (Clupea harengus) for two years. Stable isotope ratios were measured via isotope ratio mass spectrometry in three of their tissues and related to values of these markers in their diet. Diet-tissue isotope enrichment (trophic enrichment factor, TEF) values between dietary herring and seal tissues for carbon (Δ13 C) were +0.7 ‰ for red blood cells, +1.9 ‰ for hair and +1.1 ‰ for muscle. The TEFs for nitrogen trophic (Δ15 N) were +3.3 ‰ for red blood cells, +3.6 ‰ for hair and +4.3 ‰ for muscle. For sulphur, the Δ34 S values were +1.1 ‰ for red blood cells, +1.0 ‰ for hair and +0.9 ‰ for muscle. These enrichment values were greater than those previously measured in adult seals. This increase may be related to the higher rate of protein synthesis and catabolism in growing animals. This study is the first report on sulphur isotope enrichment values for a marine mammal species.

Using otolith organic matter to detect diet shifts in Bardiella chrysoura, during a period of environmental changes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 575:137-152 (2017) - DOI: https://doi.org/10.3354/meps12166 Using otolith organic matter to detect diet shifts in Bardiella chrysoura, during a period of environmental changes C. Sirot1,*, P. Grønkjær2, J. Brøgger Pedersen2, J. Panfili1, M. Zetina-Rejon3, A. Tripp-Valdez3, J. Ramos-Miranda4, D. Flores-Hernandez4, A. Sosa-Lopez4, A. M. Darnaude1 1Center for Marine Biodiversity, Exploitation & Conservation, UMR MARBEC, Bat. 24 - CC093, Place Eugène Bataillon, 34095 Montpellier cedex 5, France 2Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark 3Centro Interdisciplinario de Ciencias Marinas (CICIMAR-IPN), Politécnico Nacional, El Conchalito, 23096 La Paz, Baja California Sur, Mexico 4Centro de Ecologia, Pesqueria y Oceanografia de Golfo de Mexico (EPOMEX), Universidad Autonoma de Campeche, 24030 Campeche, Mexico *Corresponding author: charlott.sirot@gmail.com ABSTRACT: Accurate knowledge on fish trophic ecology and its modifications is crucial for understanding the impact of global change on ecosystems. In this context, we investigated the value of the δ13C and δ15N of otolith soluble organic matter (SOM) for identifying temporal diet shifts in American silver perch Bairdiella chrysoura over a 30-yr period characterized by strong changes in its population size and habitats within the Terminos Lagoon (Mexico). We first compared the otolith SOM isotopic signatures from present-day adults to those of muscle and the main local prey. Our results suggest that otolith SOM can be confidently extracted and analyzed for both present and past otoliths of this species. The mean otolith SOM signatures obtained (-15.92 ± 1.35‰ for δ13C and 9.38 ± 0.93‰ for δ15N) were consistent with those of the diet as 85% of the individual signatures were included within the prey isotopic niche area. Moreover, this study supports a trophic enrichment factor between diet and otolith (TEFdiet-otolith) close to 0 for δ15N, while for δ13C, the TEFotolith-muscle of +0.02‰ warrants further investigation. Then, we compared past and contemporary otolith SOM signatures to investigate temporal diet shifts in B. chrysoura. This showed that δ13C and δ15N differed significantly between the past and present period even if the temporal shift remained relatively small (respectively +1.17‰ and –0.55‰). The present study substantiates the use of otolith SOM δ13C and δ15N as a proxy of fish present and past trophic position, opening the possibility for major progress in studies of temporal changes in food web ecology. KEY WORDS: Trophic ecology · Stable isotope analysis · Coastal ecosystem · Bairdiella chrysoura · Terminos Lagoon Full text in pdf format Supplementary material PreviousNextCite this article as: Sirot C, Grønkjær P, Pedersen JB, Panfili J and others (2017) Using otolith organic matter to detect diet shifts in Bardiella chrysoura, during a period of environmental changes. Mar Ecol Prog Ser 575:137-152. https://doi.org/10.3354/meps12166 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 575. Online publication date: July 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Protistan microzooplankton and the trophic position of tuna: quantifying the trophic link between micro- and mesozooplankton in marine foodwebs

Abstract The importance of the trophic link between <200-µm protistan microzooplankton and mesozooplankton is a cornerstone of modern understanding of foodweb structure of marine pelagic ecosystems that is well demonstrated in experimentally measured contributions of protistan consumers to mesozooplankton diets, in constrained global budgets, and in regional studies that show the inadequacies of meeting zooplankton metabolic requirements by herbivory alone. Nonetheless, protistan trophic steps are poorly reflected in stable isotope analyses by standard methods and systematically neglected in fisheries-related trophic research, which focuses instead on interactions that can be measured in stomach contents. Here, we apply recent advances in compound-specific isotope analysis of amino acids (CSIA-AA) based on alanine as a trophic indicator of protistan foodweb steps to evaluate the implications of lower foodweb structure on trophic position (TP) estimates of tunas. CSIA-AA results for mesozooplankton of the subtropical North Pacific suggest that tuna TPs are underestimated by 0.9, which give rise to new TP estimates of 4.7–5.4 for the three main tuna species of that region. These, in turn, are used to compute a trophic enrichment factor (TEF = 4.45) based on alanine that includes 15N enrichments for protistan consumers and can be applied more broadly in the region. Accounting for the magnitude and variability of protistan trophic steps in the foodwebs supporting pelagic fisheries has important implications for understanding regional variability in energy flows and foodweb structure and their temporal responses to climate change.

The effect of trophic level on individual amino acid δ15N values in a terrestrial ruminant food web

ABSTRACTBulk collagen δ15N analysis is widely used to investigate past diet and trophic positions, but these values average the δ15N values of the constituent amino acids. Compound–specific isotope analysis of amino acids (AAs) can help elucidate the complex metabolic effects underpinning bulk δ15N values. Although trophic level effects on individual AA δ15N values have been investigated in aquatic and terrestrial invertebrate food webs, most archaeological applications involve terrestrial herbivores, hence a greater understanding of these effects between diet and consumer in this food chain is required. The North Wyke Farm Platform provided baseline nitrogen isotope information for cattle grazing on a Lolium perenne-dominated pasture. Bulk dentine δ15N values show a shift expected for a one trophic level increase, but obscure insight into the underlying metabolic processes that cause this change in value. However, determination of AA δ15N values of hydrolysable plant protein and cattle tooth dentine clarifies the trophic effect on consumer AA δ15N values. The observed trophic shift in the studied system is different from previously studied food webs, with a trophic enrichment factor, based on the δ15N values of glutamate and phenylalanine, of 4.0‰ compared to 7.6‰ commonly used in ecological and archaeological studies. This emphasises the need to understand the trophic shifts in the particular food web being investigated in order to apply isotopic investigations in archaeological contexts.

Deciphering the structure of the West Greenland marine food web using stable isotopes (δ13C, δ15N)

The Arctic is facing major environmental changes impacting marine biodiversity and ecosystem functioning. One way of assessing the responses of an ecosystem to these changes is to quantitatively study food web dynamics. Here, we used stable isotope (δ15N and δ13C) analyses of 39 Arctic marine species to investigate trophic relationships and isotopic niches of the West Greenland food web in 2000–2004. The lowest δ15N values were found for suspension feeding blue mussel (Mytilus edulis; 6.1 ‰) and the highest for polar bear (Ursus maritimus; 20.2 ‰). For δ13C, copepods (Calanus spp.) had the lowest values (−20.4 ‰) and snow crab (Chionoecetes opilio) the highest values (−15.8 ‰). Our results show that the three trophic enrichment factor (TEF) approaches used to quantify species trophic positions (fixed TEF of 3.8 and 3.4 ‰ or scaled TEF) did not generally affect trophic modelling and provided similar conclusions. Overall, the findings in this study are in good agreement with previous investigations of other Arctic marine ecosystems. Interestingly, we found little overlap of core isotopic niches used by the four investigated functional groups (mammals, seabirds, fish and invertebrates), except for seabirds and fish where an overlap of 24 % was found. These results provide new insights into species and functional group interactions, as well as into the food web structure and ecosystem functioning of an important Arctic region that can be used as a template to guide future modelling of carbon, energy and contaminant flow in the region.

Variation in δ13C and δ15N trophic enrichment factors among Hyalella azteca amphipods from different lakes

Stable isotopes are a powerful tool used to study the diets of animals because they provide information on food assimilated over an extended period. However, trophic enrichment factors used to reconstruct diets sometimes vary substantially, even among animals from the same trophic level. The goal of this study was to verify if trophic enrichment factors vary among animals as similar as Hyalella azteca amphipods from different lakes. We compared the carbon and nitrogen isotopic compositions of amphipods from different lakes fed on leaf detritus and on periphyton. Amphipods showed significant differences in their trophic enrichment factors among treatments (about 3.0‰ for carbon and nitrogen). The trophic enrichment factor of carbon was more affected by the food type, whereas the trophic enrichment factor of nitrogen was more affected by lake of origin. We estimated that amphipods had a tissue turnover of 25 days for carbon and 34 days for nitrogen. Our study showed that animals from different lakes can exhibit substantial variation in their trophic enrichment factors. This strengthens the view that trophic enrichment factors specific to a study system should be used whenever possible to reconstruct the in situ diet of consumers.

Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms.

Estimating trophic structures is a common approach used to retrieve information regarding energy pathways, predation, and competition in complex ecosystems. The application of amino acid (AA) compound-specific nitrogen (N) isotope analysis (CSIA) is a relatively new method used to estimate trophic position (TP) and feeding relationships in diverse organisms. Here, we conducted the first meta-analysis of δ(15)N AA values from measurements of 359 marine species covering four trophic levels, and compared TP estimates from AA-CSIA to literature values derived from food items, gut or stomach content analysis. We tested whether the AA trophic enrichment factor (TEF), or the (15)N enrichment among different individual AAs is constant across trophic levels and whether inclusion of δ(15)N values from multiple AAs improves TP estimation. For the TEF of glutamic acid relative to phenylalanine (Phe) we found an average value of 6.6‰ across all taxa, which is significantly lower than the commonly applied 7.6‰. We found that organism feeding ecology influences TEF values of several trophic AAs relative to Phe, with significantly higher TEF values for herbivores compared to omnivores and carnivores, while TEF values were also significantly lower for animals excreting urea compared to ammonium. Based on the comparison of multiple model structures using the metadata of δ(15)N AA values we show that increasing the number of AAs in principle improves precision in TP estimation. This meta-analysis clarifies the advantages and limitations of using individual δ(15)N AA values as tools in trophic ecology and provides a guideline for the future application of AA-CSIA to food web studies.