In the eastern Pacific Ocean, climate-related events may also directly affect sea turtle populations by impacting food web dynamics Chavez et al. Because sea turtles are sensitive to oceanic and terrestrial temperature shifts Davenport ; Fuentes et al. An example of this process is the decline of sea grass Zostera marina in modern eastern Pacific coastal lagoons Riosmena-Rodriguez et al. Sea surface temperatures were cooler during the s than today Kennedy et al.
This suggests that sea turtle diets may have shifted during the mid th century due to broad changes in sea surface temperature that directly affected predator-prey relationships and dietary resources Etnoyer et al. These background changes in sea surface temperatures and thus sea turtle habitats leave an unanswered question: were sea turtle diets significantly different in the 19 th and 20 th centuries?
We analyze Gold Rush-era sea turtle bone stable isotopes, as a proxy for dietary and habitat ecology, and compare these values with modern specimens to determine if there is evidence for change in turtle diet between the s and today. Because sea turtles forage on a diverse range of resources, even within the same species Jones and Seminoff , identification of changing ecology is only possible if the data under consideration derive from the same species and geographic area. We therefore use ancient DNA analysis to assign a species affiliation to the archaeological specimens, and then bone collagen and apatite stable isotope analyses to identify diet i.
These stable isotopes provide a quantifiable technique to systematically examine dietary and habitat information for both 19 th century and modern sea turtles. This mixed method approach, using ancient DNA analysis alongside the analysis of multiple isotope systems, allows for the identification of Gold Rush-era sea turtle samples and a comparison of past and present dietary ecology. Precautions aimed to minimize and monitor the introduction of contamination are practiced in the laboratory. Approximately The samples were then twice submerged in DNA-free water, with the water poured off following submersion.
Samples were transferred to 1. Neither extract contained sufficient inhibitors to prevent amplification of turkey DNA control. Sequences of this amplicon spanning to can be used as a barcode to discriminate between all extant sea turtles e.
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PCRs were conducted with full concentration extracts and dilutions of those extracts. PCR reaction conditions were as described above. Sequencher version 5. After cutting a small portion of bulk bone, we demineralized the sea turtle samples in 0. Lipid extraction involved immersing the samples in a solution of chloroform:methanol C 2 H 5 Cl 3 for 24 hours repeated three times. We sonicated samples for 15 minutes to ensure complete chemical saturation after each immersion.
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At the end of 72 hours we rinsed all samples to neutrality and lyophilized the samples for 24 hours. Approximately 0. We weighed hydrogen standards and samples into silver capsules and allowed the samples to sit in the laboratory for at least two weeks before analysis to ensure equilibrium between the exchangeable hydrogen in tissue and local atmosphere Sauer et al. The H 3 factor is 5.
Weight percent carbon and nitrogen concentrations provide a measure of collagen contamination Ambrose Sea turtle samples ranged between 2. After the removal of organics the samples were rinsed to neutrality using a combination of deionized water and centrifugation. For removal of labile carbonates we treated the samples with 0. All samples were vortexed after 15 minutes to ensure chemical saturation. Samples were rinsed to neutrality and then left to air-dry for 24 hours in a fume hood.
Finally, approximately 8. Vienna Pee Dee Belemnite V-PDB is the internationally accepted standard used in this study for bone apatite carbon and oxygen isotopes. Studies of living sea turtle stable isotopes are typically conducted on skin, blood and plasma tissues non-invasively to understand Cheloniidae isotopic discrimination, foraging ecology, and migration Arthur et al.
The addition of bone collagen and apatite analyses also provides insights into the latter processes, specifically foraging ecology, and for the purposes of this study, helps provide a dataset to compare modern and archaeological samples. Pioneering work on sea turtle bone stable isotopes has demonstrated their value in understanding sea turtle and ocean water physiological processes, species-specific identifications Biasatti , , isotopic assimilation and paleoclimatic relationships Coulson et al.
In addition, bone collagen comparisons occur in two forms. Map of the location of eastern Pacific Ocean sea turtle specimens discussed in text. As the archaeological samples were from bones that were over years old, there are two corrections required to make our dataset comparable with modern eastern Pacific sea turtles. We apply a —0. These corrections allow our archaeological bone samples to more directly compare with bone and non-bone tissues from modern sea turtles.
All analyses and visualizations were conducted in R 3. Summary of stable isotope results for the Gold Rush-era sea turtle specimens from San Francisco, California. Comparison of corrected bone collagen-to-skin values in both Gold Rush sea turtles see methods; following Turner Tomaszewicz et al. Mean and standard deviation bars reported, if available. However, zooarchaeological analysis was unable to distinguish these specimens as green sea turtles due to morphological similarity between the recovered elements and modern sea turtle skeletal comparatives.
Only the application of aDNA techniques provided final confirmation. Difficulty in identifying archaeological sea turtle remains is a common problem for zooarchaeologists. Bone apatite studies have suggested that it is possible to identify sea turtles based on differences in carbon isotopes Biasatti , , but results from our study can neither support nor refute this argument, due to our small sample size. Modern eastern Pacific green sea turtles are omnivorous and consume sea grasses, algae and invertebrates, but this varies with foraging location i.
These location-specific variables make comparisons between Gold Rush and modern sea turtle specimens difficult, especially given that both s samples lack exact data on their ontogenetic age, date of capture and location of capture. Given that bone collagen primarily reflects dietary protein sources Ambrose and Norr ; Lee-Thorp et al. These Gold Rush-era sea turtles were removed from ocean water and were kept alive aboard ships for weeks, if not months, without food Conrad and Pastron , during their transport to San Francisco. In plants and birds, stress can cause oxygen, hydrogen Farris and Strain ; Yakir et al.
Finally, stable hydrogen isotopes from bone collagen may also provide an alternative source for understanding foraging ecology for both Gold Rush-era specimens. Hydrogen isotopes assimilate into tissues from diet and water Hobson et al. Eastern Pacific sea turtle populations are currently recovering from steep declines during the 20 th century. The results of this study show little difference in eastern Pacific Ocean environmental and foraging dynamics since the s, but sample size limits more definitive conclusions.
On one hand, isotope results may support evidence suggesting that major declines in sea turtle populations derive from anthropogenic over-exploitation, egg collection, by-catch and not habitat change, but on the other hand, these results may simply indicate that our 19 th century samples fall within the range of modern sea turtle isotopic variation due to other unknown reasons.
We emphasize the need for additional historic ecological studies combining modern and ancient samples, and future controlled feeding and dietary studies to understand how carbon, nitrogen, oxygen and hydrogen stable isotopes assimilate, discriminate, and turn over between tissues in sea turtles. With these additional data it will be possible to employ long-term testing of sea turtle remains from archaeological sites worldwide e. These data may help identify habitat and genetic changes that can support current and future conservation and protection programs for these important, endangered species.
Finally, thank you to two reviewers for their detailed comments and advice. Ambrose, SH. Journal of Archaeological Science , — Ambrose, SH and Norr, L. Berlin: Springer-Verlag. Endangered Species Research , 3: 43— Armitage, PL.
Odyssey Marine Exploration , 2— Ontogenetic changes in diet and habitat use in green sea turtle Chelonia mydas life history. Marine Ecology Progress Series , — Ecology , 95 5 : — Bancroft, HH. History of California Vol. VI — Biasatti, DM. Stable carbon isotopic profiles of sea turtle humeri: implications for ecology and physiology.
Palaeogeography, Palaeoclimatology, Palaeoecology , — Hydrogen isotope ratios in animal body protein reflect trophic level. Journal of Animal Ecology , — Bjorndal, KA. Foraging ecology and nutrition of sea turtles. Cabana, G and Rasmussen, JB. View Citation. Christ, A. Hayden, V.
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Stegall, S. Farley, C. Stricker, J. Mellish, J. Maniscalco, J. Waite, V. Burkanov, and K. Age-specific vibrissae growth rates: a tool for determining the timing of ecologically important events in Steller sea lions. Marine Mammal Science 31 3 : DOI: Rossman, Sam; Ostrom, Peggy H. Rossman, S. Stolen, N. Barros, H. Gandhi, P. Ostrom, C. Stricker, and R. Individual specialization in the foraging habits of female bottlenose dolphins living in a trophically diverse and habitat rich estuary. Oecologia Year Published: Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States.
Scherer, Rick D. Scherer, R. Doll, L. Rea, A. Christ, C. Stricker, B. Witteveen, T. Kline, C.
Kurle, and M. Isotope values in pup whiskers reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus. Marine Ecology Progress Series Year Published: Improved arrival-date estimates of Arctic-breeding Dunlin Calidris alpina arcticola The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. Doll, Andrew C. Doll, A. Lanctot, C. Stricker, and M. Comparing efficacies of experimental, theoretical and in-situ stable carbon isotope turnover rates to determine timing of Dunlin Calidris alpina arcticola migration.
The Auk Year Published: Unexpected hydrogen isotope variation in oceanic pelagic seabirds Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. Ostrom, Peggy H.
Stable Isotope Ecology and Ecosystems Functioning
Ostrom, P. Saturday 6 April Short letter of presentation. Letter of Support from tutor or supervisor.
The course will be a combinations of Lectures. Practical experience. Apart from the lectures, there will be group projects to complete and hands-on practical experience with analysing data etc. Course ID. Course Fee.