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Sanchez CL, Casale P, Bunbury N, A'Bear L, Banane V, Benstrong F, Bielsa M, Jones CW, Koester A, Murasko S, van Rooyen MC, Fleischer-Dogley F, Ceriani SA. Fine-scale foraging ecology and habitat use of sympatric green and hawksbill turtles in the Western Indian ocean. MARINE ENVIRONMENTAL RESEARCH 2024; 198:106529. [PMID: 38688109 DOI: 10.1016/j.marenvres.2024.106529] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2023] [Revised: 04/01/2024] [Accepted: 04/26/2024] [Indexed: 05/02/2024]
Abstract
Using stable isotope analysis of carbon and nitrogen of turtle tissues and putative prey items, we investigated the diet of immature green turtles and hawksbill turtles foraging in the lagoon of Aldabra Atoll, a relatively undisturbed atoll in the southern Seychelles. Aldabra offers a unique environment for understanding sea turtle ecology. Green turtles mostly consumed seagrass and brown algae while hawksbill turtles mainly consumed mangroves and invertebrates. Green turtles showed a dietary shift with size (a proxy for age). There was minimal niche overlap between species and evidence of small-scale foraging site fidelity with turtle tissue reflecting site-specific prey. This highlights the ecological importance of seagrass and mangrove habitats and suggests that turtles play a role in controlling algal biomass at Aldabra. This study is the first to closely examine the foraging ecology of these sympatric turtle species in the Western Indian Ocean, a globally important region for both species.
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Affiliation(s)
- Cheryl L Sanchez
- Department of Biology, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy; Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Saint Petersburg, FL, USA; Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | - Paolo Casale
- Department of Biology, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy.
| | - Nancy Bunbury
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles; Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn TR10 9FE, UK
| | - Luke A'Bear
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | - Veronique Banane
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | - Frances Benstrong
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | - Maria Bielsa
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | | | - Anna Koester
- Seychelles Islands Foundation, Mahé, P.O. Box 853, Victoria, Seychelles
| | - Susan Murasko
- Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Saint Petersburg, FL, USA
| | | | | | - Simona A Ceriani
- Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Saint Petersburg, FL, USA
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Ramirez MD, Avens L, Meylan AB, Shaver DJ, Stahl AR, Meylan PA, Clark JM, Howell LN, Stacy BA, Teas WG, McMahon KW. Dietary plasticity linked to divergent growth trajectories in a critically endangered sea turtle. Front Ecol Evol 2023. [DOI: 10.3389/fevo.2023.1050582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023] Open
Abstract
Foraging habitat selection and diet quality are key factors that influence individual fitness and meta-population dynamics through effects on demographic rates. There is growing evidence that sea turtles exhibit regional differences in somatic growth linked to alternative dispersal patterns during the oceanic life stage. Yet, the role of habitat quality and diet in shaping somatic growth rates is poorly understood. Here, we evaluate whether diet variation is linked to regional growth variation in hawksbill sea turtles (Eretmochelys imbricata), which grow significantly slower in Texas, United States versus Florida, United States, through novel integrations of skeletal growth, gastrointestinal content (GI), and bulk tissue and amino acid (AA)-specific stable nitrogen (δ15N) and carbon (δ13C) isotope analyses. We also used AA δ15N ΣV values (heterotrophic bacterial re-synthesis index) and δ13C essential AA (δ13CEAA) fingerprinting to test assumptions about the energy sources fueling hawksbill food webs regionally. GI content analyses, framed within a global synthesis of hawksbill dietary plasticity, revealed that relatively fast-growing hawksbills stranded in Florida conformed with assumptions of extensive spongivory for this species. In contrast, relatively slow-growing hawksbills stranded in Texas consumed considerable amounts of non-sponge invertebrate prey and appear to forage higher in the food web as indicated by isotopic niche metrics and higher AA δ15N-based trophic position estimates internally indexed to baseline nitrogen isotope variation. However, regional differences in estimated trophic position may also be driven by unique isotope dynamics of sponge food webs. AA δ15N ΣV values and δ13CEAA fingerprinting indicated minimal bacterial re-synthesis of organic matter (ΣV < 2) and that eukaryotic microalgae were the primary energy source supporting hawksbill food webs. These findings run contrary to assumptions that hawksbill diets predominantly comprise high microbial abundance sponges expected to primarily derive energy from bacterial symbionts. Our findings suggest alternative foraging patterns could underlie regional variation in hawksbill growth rates, as divergence from typical sponge prey might correspond with increased energy expenditure and reduced foraging success or diet quality. As a result, differential dispersal patterns may infer substantial individual and population fitness costs and represent a previously unrecognized challenge to the persistence and recovery of this critically endangered species.
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Chandelier G, Kiszka JJ, Dulau-Drouot V, Jean C, Poirout T, Estrade V, Barret M, Fayan J, Jaquemet S. Isotopic niche partitioning of co-occurring large marine vertebrates around an Indian ocean tropical oceanic island. MARINE ENVIRONMENTAL RESEARCH 2023; 183:105835. [PMID: 36527765 DOI: 10.1016/j.marenvres.2022.105835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 11/23/2022] [Accepted: 11/25/2022] [Indexed: 06/17/2023]
Abstract
Tropical oceans host a high diversity of species, including large marine consumers. In these oligotrophic ecosystems, oceanic islands often favour the aggregation of species and biomass as they provide feeding opportunities related to the mechanisms of island mass effect. As such, the waters surrounding La Reunion (Southwest Indian Ocean) host seabirds, large pelagic teleosts, elasmobranchs, delphinids and sea turtles. Isotopic niche partitioning and comparison of trophic levels among these species (n = 21) were investigated using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Overall, δ13C values were highly variable among taxa, indicating that the species exploit multiple foraging habitats along a coast-open ocean gradient. Overlap in δ15N values was limited, except for teleost species, the two species of sea turtles and two species of delphinids, the Indo-pacific bottlenose dolphin (Tursiops aduncus) and the Spinner dolphin (Stellena longirostris). Stable isotope analyses of samples collected over a 9-years period on different tissues with different integration times provide a consistent picture of the structure of the community of large marine vertebrates species around La Reunion and highlight the underlying mechanisms to limit the competition between species. The wide range of isotopic values confirms that large marine vertebrates have different trophic roles in coastal marine food webs around this oceanic island, which limits their potential of competitive interactions for resources.
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Affiliation(s)
- Guillaume Chandelier
- UMR Entropie, Université de la Réunion, 15 avenue René Cassin, 97744, Saint Denis Cédex 9, Ile de La Réunion, France
| | - Jeremy J Kiszka
- Department of Biological Sciences, Florida International University, 3000 NE 151th Street, North Miami, FL, 33181, USA
| | - Violaine Dulau-Drouot
- Groupe Local d'Observation et d'Identification des Cétacés (GLOBICE), 97432, Ravine des Cabris, Ile de La Réunion, France
| | - Claire Jean
- Kelonia, l'observatoire des tortues marines, 46 rue du Général de Gaulle, 97436, Saint Leu, Ile de La Réunion, France
| | - Thomas Poirout
- UMR Entropie, Université de la Réunion, 15 avenue René Cassin, 97744, Saint Denis Cédex 9, Ile de La Réunion, France
| | - Vanessa Estrade
- Groupe Local d'Observation et d'Identification des Cétacés (GLOBICE), 97432, Ravine des Cabris, Ile de La Réunion, France
| | - Mathieu Barret
- Kelonia, l'observatoire des tortues marines, 46 rue du Général de Gaulle, 97436, Saint Leu, Ile de La Réunion, France
| | - Jacques Fayan
- Brigade Nature Océan Indien (BNOI), 12 All de la forêt parc de la providence, 97400, Saint-Denis, Ile de La Réunion, France
| | - Sébastien Jaquemet
- UMR Entropie, Université de la Réunion, 15 avenue René Cassin, 97744, Saint Denis Cédex 9, Ile de La Réunion, France.
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Turner Tomaszewicz CN, Liles MJ, Avens L, Seminoff JA. Tracking movements and growth of post-hatchling to adult hawksbill sea turtles using skeleto+iso. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.983260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In the eastern Pacific Ocean, hawksbill sea turtles (Eretmochelys imbricata) are adapted to use coastal habitats and ecosystems uncharacteristic of most other sea turtles. Once considered extirpated from this region, hawksbills had sought refuge in estuaries, nesting on muddy banks among the tangles of mangrove roots. This population is at high risk of bycatch during fishing efforts in the estuaries (blast fishing) and adjacent coastal rocky reefs (gillnets), and is further impacted by habitat degradation from coastal development and climate change. The conservation and population recovery of hawksbills in this region is highly dependent on management actions (e.g., nest relocation, habitat protection, bycatch mitigation), and a better understanding of how hawksbills use and move between distinct habitats will help prioritize conservation efforts. To identify multi-year habitat use and movement patterns, we used stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of skin and bone growth layers to recreate movements between two isotopically distinct habitats, a nearshore rocky reef and a mangrove estuary, the latter distinguishable by low δ13C and δ15N values characteristic of a mangrove-based foodweb. We applied skeletochronology with sequential δ13C and δ15N analysis of annual growth layers, “skeleto+iso,” to a dataset of 70 hawksbill humeri collected from coastal El Salvador. The results revealed at least two unique habitat-use patterns. All turtles, regardless of stranding location, spent time outside of the mangrove estuaries during their early juvenile years (< 35 cm curved carapace length, CCL, age 0–5), showing that an oceanic juvenile stage is likely for this population. Juveniles ca. > 35 cm then began to recruit to nearshore areas, but showed divergent habitat-use as some of turtles occupied the coastal rocky reefs, while others settled into the mangrove estuaries. For turtles recruiting to the estuaries, settlement age and size ranged from 3 to 13 years and 35–65 cm CCL. For the adult turtles, age-at-sexual-maturity ranged from 16 to 26 years, and the maximum reproductive longevity observed was 33 years. The skeleto+iso also showed that adult hawksbills have long-term habitat fidelity, and the results demonstrate the importance of both mangrove estuary and nearshore rocky reefs to the conservation of hawksbills in the eastern Pacific.
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Seminoff JA, Komoroske LM, Amorocho D, Arauz R, Chacón‐Chaverrí D, Paz N, Dutton PH, Donoso M, Heidemeyer M, Hoeffer G, Todd Jones T, Kelez S, Lemons GE, Rguez‐Baron JM, Sampson L, Santos Baca L, Steiner T, Vejar Rubio M, Zárate P, Zavala‐Norzagaray A, Popp BN. Large‐scale patterns of green turtle trophic ecology in the eastern Pacific Ocean. Ecosphere 2021. [DOI: 10.1002/ecs2.3479] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- Jeffrey A. Seminoff
- NOAA‐National Marine Fisheries Service Southwest Fisheries Science Center La Jolla California USA
| | - Lisa M. Komoroske
- NOAA‐National Marine Fisheries Service Southwest Fisheries Science Center La Jolla California USA
- Department of Environmental Conservation University of Massachusetts Amherst Amherst Massachusetts USA
| | - Diego Amorocho
- Centro De Investigacion Para El Manejo Ambiental y El Desarrollo Cali Colombia
| | - Randall Arauz
- Fins Attached Marine Research and Conservation Colorado Springs Colorado USA
| | | | - Nelly Paz
- Areas Costeras y Recursos Marinos Pisco Perú
| | - Peter H. Dutton
- NOAA‐National Marine Fisheries Service Southwest Fisheries Science Center La Jolla California USA
| | | | - Maike Heidemeyer
- Escuela de Biología Centro de Investigación en Biología Celular y Molecular Centro de Investigación en Ciencas del Mar y Limnología (CIMAR) Universidad de Costa Rica San Pedro Costa Rica
| | | | - T. Todd Jones
- Pacific Islands Fisheries Science Center NOAA‐National Marine Fisheries Service Honolulu Hawaii USA
| | | | - Garrett E. Lemons
- NOAA‐National Marine Fisheries Service Southwest Fisheries Science Center La Jolla California USA
| | - Juan M. Rguez‐Baron
- Universidad Autónoma de Baja California Sur La Paz Baja California Sur México
| | - Laura Sampson
- Department of Biology Universidad del Valle Cali Colombia
| | - Lucía Santos Baca
- Department of Natural Resources Centro de Investigaciones Biológicas del Noroeste La Paz México
| | - Todd Steiner
- Turtle Island Restoration Network Forest Knolls California USA
- MigraMar Forest Knolls California USA
| | - Maria Vejar Rubio
- Instituto Politécnico Nacional CIIDIR Unidad Sinaloa Guasave Sinaloa México
| | - Patricia Zárate
- MigraMar Forest Knolls California USA
- Department of Biology University of Florida Gainesville Florida USA
| | | | - Brian N. Popp
- Department of Earth Sciences University of Hawai'i at Manoa Honolulu Hawaii USA
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Pagès Barceló L, Seminoff JA, Vander Zanden HB, Jones TT, Bjorndal KA, Bolten AB, Mustin W, Busquets-Vass G, Newsome SD. Hydrogen isotope assimilation and discrimination in green turtles. J Exp Biol 2021; 224:238723. [PMID: 33653718 DOI: 10.1242/jeb.231431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 02/22/2021] [Indexed: 11/20/2022]
Abstract
Although hydrogen isotopes (δ2H) are commonly used as tracers of animal movement, minimal research has investigated the use of δ2H as a proxy to quantify resource and habitat use. While carbon and nitrogen are ultimately derived from a single source (food), the proportion of hydrogen in consumer tissues originates from two distinct sources: body water and food. Before hydrogen isotopes can be effectively used as a resource and habitat tracer, we need estimates of (net) discrimination factors (Δ2HNet) that account for the physiologically mediated differences in the δ2H values of animal tissues relative to that of the food and water sources they use to synthesize tissues. Here, we estimated Δ2HNet in captive green turtles (Chelonia mydas) by measuring the δ2H values of tissues (epidermis and blood components) and dietary macromolecules collected in two controlled feeding experiments. Tissue δ2H and Δ2HNet values varied systematically among tissues, with epidermis having higher δ2H and Δ2HNet values than blood components, which mirrors patterns between keratinaceous tissues (feathers, hair) and blood in birds and mammals. Serum/plasma of adult female green turtles had significantly lower δ2H values compared with juveniles, likely due to increased lipid mobilization associated with reproduction. This is the first study to quantify Δ2HNet values in a marine ectotherm, and we anticipate that our results will further refine the use of δ2H analysis to better understand animal resource and habitat use in marine ecosystems, especially coastal areas fueled by a combination of marine (e.g. micro/macroalgae and seagrass) and terrestrial (e.g. mangroves) primary production.
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Affiliation(s)
| | - Jeffrey A Seminoff
- National Oceanic and Atmospheric Administration-National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA 92037, USA
| | | | - T Todd Jones
- NOAA Fisheries, Pacific Islands Fisheries Science Center, Honolulu, HI 96818, USA
| | - Karen A Bjorndal
- Department of Biology, University of Florida, Gainesville, FL 32611, USA
| | - Alan B Bolten
- Department of Biology, University of Florida, Gainesville, FL 32611, USA
| | - Walter Mustin
- Cayman Turtle Conservation and Education Center, Grand Cayman KY1-1301, Cayman Islands
| | - Geraldine Busquets-Vass
- Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA.,Centro de Investigación Científica y Educación Superior de Ensenada, Unidad La Paz, Laboratorio de Macroecología Marina, Baja California Sur 23050, Mexico
| | - Seth D Newsome
- Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA
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Guiry EJ, Hunt BPV. Integrating fish scale and bone isotopic compositions for 'deep time' retrospective studies. MARINE ENVIRONMENTAL RESEARCH 2020; 160:104982. [PMID: 32907720 DOI: 10.1016/j.marenvres.2020.104982] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 03/27/2020] [Accepted: 04/01/2020] [Indexed: 06/11/2023]
Abstract
Isotopic studies of archived fish scales have tremendous potential to develop long-term retrospectives that provide important insights into how humans have altered aquatic ecosystems. However, fish specimens in museum archives and other repositories typically date to time periods when the impacts of industrial societies may have already caused profound environmental changes. Archaeological fish bones offer an opportunity to bridge this key temporal gap by providing samples spanning from the recent past to as far back as the Pleistocene. Collagen is the primary protein component of both fish scale and bone, but the comparability of isotopic compositions from these tissues has not been established experimentally. To lay the framework for integrating isotopic datasets from these tissues, we compare δ13C and δ15N of bone and scale collagen, as well as other tissues, from fish with life-time controlled diets. Results show that while there is no difference in δ13C between scale and bone collagen, there may be a very slight but meaningful inter-tissue offset in δ15N (<0.3‰). We discuss potential sources of δ15N variation in scale and bone collagen measurements. Because there is no difference in scale and bone δ13C, and the observed offset in δ15N is very small (less than analytical uncertainty in many studies), our findings demonstrate that collagen isotopic compositions from these tissues should be directly comparable when integrating datasets from modern and ancient samples to build more powerful, millennium-scale isotopic times series. In linking isotopic compositions of collagen from modern, historical (scales), and archaeological (bones) fish, our findings open the way for more nuanced contextualization of how ecosystems functioned prior to large-scale exploitation and how they have responded to mounting anthropogenic pressures in the intervening centuries.
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Affiliation(s)
- Eric J Guiry
- Department of Anthropology, Trent University, 1600 West Bank Drive, Peterborough, ON, K9L 0G2, Canada; School of Archaeology and Ancient History, University of Leicester, University Road, Leicester, LE17RH, UK; Department of Anthropology, University of British Columbia, 6306 NW Marine Drive, Vancouver, BC, V6T 1Z1, Canada.
| | - Brian P V Hunt
- Institute for the Oceans and Fisheries, University of British Columbia, Aquatic Ecosystems Research Laboratory, 2202 Main Mall, Vancouver, BC, V6T 1Z4, Canada; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020 - 2207 Main Mall, Vancouver, BC, V6T 1Z4, Canada; Hakai Institute, PO Box 309, Heriot Bay, BC, V0P 1H0, Canada
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Vanderklift MA, Pillans RD, Robson NA, Skrzypek G, Stubbs JL, Tucker AD. Comparisons of stable isotope composition among tissues of green turtles. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8839. [PMID: 32436593 DOI: 10.1002/rcm.8839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 05/08/2020] [Accepted: 05/18/2020] [Indexed: 06/11/2023]
Abstract
UNLABELLED Ecologists often need to make choices about what body parts (tissues or organs) of an animal to sample. The decision is typically guided by the need to treat animals as humanely as possible, as well as the information that different body parts can provide. When using stable isotopes, decisions are also influenced by whether specimens would require preservation, and whether they have properties (such as high lipid concentrations) that would influence measurements. Sometimes we cannot use a preferred tissue (for example, because of ethical or logistical constraints), and in such cases an ability to reliably predict stable isotope composition for one tissue from data yielded by another would be useful. METHODS In this study we analysed multiple tissues (skin, whole blood, red blood cells, plasma and nail) from green turtles (Chelonia mydas) to evaluate variation in C:N ratios, and test hypotheses about the intercept and slope of regressions of stable carbon and nitrogen isotope compositions among tissues. RESULTS Regression models revealed that linear relationships were present for most comparisons, except those involving the δ13 C of skin, and the slopes (β1 ) of most regressions were different from unity. The C:N ratios of skin were significantly higher and more variable than those of other tissues. The δ13 C and δ15 N of nail were highly correlated with those of the whole blood, red blood cells and plasma. Nail and red blood cells showed low variation in C:N. CONCLUSIONS The patterns in slopes of regressions indicate that comparisons of measurements yielded by different tissues of wild animals are complicated by the fact that the tissues are unlikely to be in isotopic equilibrium with their diet. Of the tissues used in this study, nail is simple to collect, requires minimal disturbance to the animal and no special preservation; these traits should make it attractive to turtle ecologists, but more information is needed on aspects such as growth rates.
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Affiliation(s)
- Mathew A Vanderklift
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
| | - Richard D Pillans
- CSIRO Oceans & Atmosphere, Biosciences Precinct, St Lucia, Queensland, 4067, Australia
| | - Natalie A Robson
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
| | - Grzegorz Skrzypek
- School of Biological Sciences, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Jessica L Stubbs
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
- School of Biological Sciences, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Anton D Tucker
- Marine Science Program, Department of Biodiversity, Conservation and Attractions, Kensington, WA, 6151, Australia
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9
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Guiry EJ, Szpak P. Quality control for modern bone collagen stable carbon and nitrogen isotope measurements. Methods Ecol Evol 2020. [DOI: 10.1111/2041-210x.13433] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eric J. Guiry
- Department of Anthropology Trent University Peterborough ON Canada
- School of Archaeology and Ancient History University of Leicester Leicester UK
| | - Paul Szpak
- Department of Anthropology Trent University Peterborough ON Canada
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Figgener C, Bernardo J, Plotkin PT. Beyond trophic morphology: stable isotopes reveal ubiquitous versatility in marine turtle trophic ecology. Biol Rev Camb Philos Soc 2019; 94:1947-1973. [PMID: 31338959 PMCID: PMC6899600 DOI: 10.1111/brv.12543] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 06/07/2019] [Accepted: 06/13/2019] [Indexed: 11/30/2022]
Abstract
The idea that interspecific variation in trophic morphology among closely related species effectively permits resource partitioning has driven research on ecological radiation since Darwin first described variation in beak morphology among Geospiza. Marine turtles comprise an ecological radiation in which interspecific differences in trophic morphology have similarly been implicated as a pathway to ecopartition the marine realm, in both extant and extinct species. Because marine turtles are charismatic flagship species of conservation concern, their trophic ecology has been studied intensively using stable isotope analyses to gain insights into habitat use and diet, principally to inform conservation management. This legion of studies provides an unparalleled opportunity to examine ecological partitioning across numerous hierarchical levels that heretofore has not been applied to any other ecological radiation. Our contribution aims to provide a quantitative analysis of interspecific variation and a comprehensive review of intraspecific variation in trophic ecology across different hierarchical levels marshalling insights about realised trophic ecology derived from stable isotopes. We reviewed 113 stable isotope studies, mostly involving single species, and conducted a meta-analysis of data from adults to elucidate differences in trophic ecology among species. Our study reveals a more intricate hierarchy of ecopartitioning by marine turtles than previously recognised based on trophic morphology and dietary analyses. We found strong statistical support for interspecific partitioning, as well as a continuum of intraspecific trophic sub-specialisation in most species across several hierarchical levels. This ubiquity of trophic specialisation across many hierarchical levels exposes a far more complex view of trophic ecology and resource-axis exploitation than suggested by species diversity alone. Not only do species segregate along many widely understood axes such as body size, macrohabitat, and trophic morphology but the general pattern revealed by isotopic studies is one of microhabitat segregation and variation in foraging behaviour within species, within populations, and among individuals. These findings are highly relevant to conservation management because they imply ecological non-exchangeability, which introduces a new dimension beyond that of genetic stocks which drives current conservation planning. Perhaps the most remarkable finding from our data synthesis is that four of six marine turtle species forage across several trophic levels. This pattern is unlike that seen in other large marine predators, which forage at a single trophic level according to stable isotopes. This finding affirms suggestions that marine turtles are robust sentinels of ocean health and likely stabilise marine food webs. This insight has broader significance for studies of marine food webs and trophic ecology of large marine predators. Beyond insights concerning marine turtle ecology and conservation, our findings also have broader implications for the study of ecological radiations. Particularly, the unrecognised complexity of ecopartitioning beyond that predicted by trophic morphology suggests that this dominant approach in adaptive radiation research likely underestimates the degree of resource overlap and that interspecific disparities in trophic morphology may often over-predict the degree of realised ecopartitioning. Hence, our findings suggest that stable isotopes can profitably be applied to study other ecological radiations and may reveal trophic variation beyond that reflected by trophic morphology.
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Affiliation(s)
- Christine Figgener
- Marine Biology Interdisciplinary ProgramTexas A&M University3258 TAMU, College StationTX77843U.S.A.
- Department of BiologyTexas A&M University3258 TAMU, College StationTX77843U.S.A.
- Department of OceanographyTexas A&M University3146 TAMU, College StationTX77843U.S.A.
| | - Joseph Bernardo
- Marine Biology Interdisciplinary ProgramTexas A&M University3258 TAMU, College StationTX77843U.S.A.
- Department of BiologyTexas A&M University3258 TAMU, College StationTX77843U.S.A.
- Program in Ecology and Evolutionary BiologyTexas A&M University2475 TAMU, College StationTX77843U.S.A.
| | - Pamela T. Plotkin
- Marine Biology Interdisciplinary ProgramTexas A&M University3258 TAMU, College StationTX77843U.S.A.
- Department of OceanographyTexas A&M University3146 TAMU, College StationTX77843U.S.A.
- Texas Sea Grant, Texas A&M University4115 TAMU, College StationTX77843U.S.A.
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Chabot RM, Ceriani SA, Seminoff JA, Mills KA, Mansfield KL. Characterizing stable isotope relationships between green turtle (Chelonia mydas) skin and unhatched eggs. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:1277-1285. [PMID: 31034695 DOI: 10.1002/rcm.8467] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 02/28/2019] [Accepted: 04/15/2019] [Indexed: 06/09/2023]
Abstract
RATIONALE Stable isotope analysis is used to understand the foraging habits and movements of a diverse set of organisms. Variability in stable isotope ratios among tissues derived from the same animal makes it difficult to compare data among study results in which different tissue types are evaluated. Isotopic relationships between two green turtle (Chelonia mydas) tissue types, skin and unhatched egg contents are unknown. Similarly, few data exist to evaluate the influence of time elapsed after oviposition (as a proxy for decomposition) on isotopic variability among unhatched eggs within the same nest. METHODS Skin and unhatched egg contents were collected from 69 adult female green turtles and associated nests at the Archie Carr National Wildlife Refuge in Florida, USA. Values of δ13 C, δ15 N, and δ34 S were measured for both tissue types using a continuous flow isotope ratio mass spectrometer. Standardized major-axis (SMA) regression was used to generate conversion equations of carbon, nitrogen, and sulfur isotope ratios between the two tissue types. Model selection frameworks consisting of single-factor linear models were employed per isotope ratio to assess how egg time-in-nest affected intraclutch isotopic variability. RESULTS Conversion equations for all three isotope ratios indicated significant relationships between skin and unhatched egg values, although model fits were lower than found in some studies examining similar patterns in other marine turtle species. The probability of increased intraclutch variability was significantly higher among eggs collected at longer intervals after deposition. CONCLUSIONS This study reports the first-ever δ13 C and δ15 N conversion equations between skin and unhatched eggs for green turtles, and the first δ34 S conversion equation for any marine turtle species. SMA regression was used to directly convert tissue values bidirectionally, unlike equations generated using ordinary least-squares regression. Issues with increased intraclutch variability at later excavation dates highlight the importance of collecting unhatched eggs as soon as possible after hatchling emergence.
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Affiliation(s)
- Ryan M Chabot
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
- Inwater Research Group, Inc., Jensen Beach, FL, USA
| | - Simona A Ceriani
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
- Florida Fish and Wildlife Conservation Commission - Fish and Wildlife Research Institute, St. Petersburg, FL, USA
| | - Jeffrey A Seminoff
- National Oceanic and Atmospheric Administration - National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, USA
| | - Kali A Mills
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
| | - Katherine L Mansfield
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
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