Kimberly J. Reich

The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages

Ignorance of the location or inaccessible locations of lifestages can impede the study and management of species. We used stable isotopes of carbon and nitrogen to identify the habitats and diets and to estimate the duration of a ‘missing’ lifestage: the early juvenile stage of the green turtle, Chelonia mydas. Stable isotopes in scute from young herbivorous green turtles in shallow-water habitats revealed that they spend 3–5 years as carnivores in oceanic habitats before making a rapid ontogenetic shift in diet and habitat. Stable isotopes in persistent and continuously growing tissues, such as some fish scales, bird bills and claws and mammal hair and claws, can be used to evaluate the ecology of inaccessible lifestages.

Individual specialists in a generalist population: results from a long-term stable isotope series.

Individual variation in resource use has often been ignored in ecological studies, but closer examination of individual patterns through time may reveal significant intrapopulation differences. Adult loggerhead sea turtles (Caretta caretta) are generalist carnivores with a wide geographical range, resulting in a broad isotopic niche. We microsampled scute, a persistent and continuously growing tissue, to examine long-term variation in resource use (up to 12 years) in 15 nesting loggerhead turtles. Using stable isotopes of nitrogen and carbon, we examined the resource use patterns (integration of diet, habitat and geographical location) and demonstrate that individual loggerheads are long-term specialists within a generalist population. We present our results in the context of a conceptual model comparing isotopic niches in specialist and generalist populations. Individual consistency may have important ecological, evolutionary and conservation consequences, such as the reduction of intraspecific competition.

Effects of Preservation Method on Stable Carbon and Nitrogen Isotope Values

Some methods of tissue preservation have significant effects on values of stable isotopes of carbon (δ13C) and nitrogen (δ15N), but studies on this topic are scattered in the literature. The goals of this study were to (1) summarize the results from studies of preservation effects in the literature and (2) test the effects of four common preservatives on δ13C and δ15N in epidermis tissue of three turtle species. Turtle tissue samples were subjected to up to five time intervals in five methods of preservation: drying at 60°C for 24 h (the control), immersion in a 70% ethanol solution, immersion in a saturated NaCl aqueous solution, freezing at −10°C in a frost‐free freezer, and immersion in a dimethyl sulfoxide (DMSO)–ethylenediaminetetraacetic acid buffer. The δ13C and δ15N values for tissues preserved in 70% ethanol and NaCl aqueous solution were not significantly different from those of tissues dried at 60°C, but samples preserved in DMSO were significantly different from dried samples. Freezing preservation had a significant effect on δ13C and δ15N at 60 d, which may have resulted from the use of a frost‐free freezer. The effects of 20 different preservative methods on δ13C and δ15N in different tissues are summarized.

Assignment of nesting loggerhead turtles to their foraging areas in the Northwest Atlantic using stable isotopes

Differential foraging area use can affect population demographics of highly migratory fauna because of differential environmental changes and anthropogenic threats among those areas. Thus, identification of foraging areas is vital for the development of effective management strategies for endangered migratory species. In this study, we assigned 375 loggerhead turtles (Caretta caretta) nesting at six locations along the east coast of the United States to their foraging areas in the Northwest Atlantic (NWA) using carbon and nitrogen stable isotope values (δ13C and δ15N). We first evaluated the epidermis δ13C and δ15N values from 60 adult loggerheads with known foraging grounds. Twenty-two females from 6 nesting beaches and 23 males from one breeding area were tracked with satellite transmitters to identify their foraging locations following breeding, and 15 adult turtles were sampled at one foraging ground. Significant trends were observed between both δ13C and δ15N values of satellite-tracked loggerheads and the latitude of the foraging grounds to which the turtles migrated, reflecting a geographic pattern in the stable isotope values. Both δ13C and δ15N values characterized three geographic areas—with distinct abiotic and biotic features—used by adult loggerheads in the NWA. Discriminant analysis assigned all 375 female loggerheads to one of the three foraging areas; 91% were assigned with probabilities of ≥80%. The proportion of nesting turtles using each foraging ground varied geographically; most turtles nesting in northern beaches (72–80%) tend to forage at higher latitudes while most turtles nesting in southern beaches (46–81%) tend to forage at lower latitudes. Stable isotopes can reveal the foraging location of loggerhead turtles in the NWA, which will allow robust analyses of foraging ground effects on demography and improve the design of management strategies for the conservation of loggerhead populations. The conclusions and methods developed in this study are also relevant for other populations of sea turtles and for other highly migratory species.

Carapace epibionts of loggerhead turtles (Caretta caretta) nesting at Canaveral National Seashore, Florida

A survey of the epibionts inhabiting the carapace of loggerhead sea turtles Caretta caretta (Linnaeus) nesting on Canaveral National Seashore, Florida was conducted from 2003–2004. Epibionts were sampled and identified to the lowest taxonomic level possible. Eleven newly documented epibiont species were observed from 52 individual loggerheads. We present the first records of sea urchins as loggerhead epibionts. Data are presented on the behavioural, physical, and ecological characteristics of some of these newly documented species to understand better the relationship between loggerhead turtles and their epibiota.

Distribution patterns of epibionts on the carapace of loggerhead turtles, Caretta caretta

The spatial distribution of epibionts on carapaces of marine turtles may be influenced by variation in recruitment dynamics, water flow patterns, and levels of disturbance on different regions of the carapace. We determined the distribution of 18 taxa of epibionts among nine zones on the carapace of 18 nesting loggerhead turtles (Caretta caretta) on Wassaw Island, Georgia, USA. Frequency of occurrence (%F) of all epibionts and each taxonomic class was determined for each zone. Distribution patterns were compared with a uniform distribution, and the distribution of each taxonomic class was compared with that of all epibionts combined. The distribution of all epibionts was significantly different from a uniform distribution, with highest densities on the posterior and vertebral zones. Distributions of each class, except Malacostraca and Cirripedia, were not significantly different from a uniform distribution across the carapace. Malacostraca was most dense on the posterior zones, whereas Cirripedia was most dense in the vertebral zones. Distributions of individual classes were all significantly different from the distribution of all epibionts combined. The distribution of all epibionts was strongly influenced by the distributions of the two dominant organisms, the chelonibiid barnacles and the caprellid amphipods.

Effect of repeated tissue sampling on growth rates of juvenile loggerhead turtles Caretta caretta

We evaluated the effect of repeated tissue sampling on growth rates of juvenile loggerhead sea turtles Caretta caretta. Samples of blood, skin, and scute (keratinized epidermal layer covering the bony shell) were collected at 3 intervals over a 120 d period from 37 loggerheads; 8 control turtles were not sampled. No infections or scarring occurred at the sampling sites, and growth in mass of experimental and control turtles was not significantly different. The sampling regime did not affect the health or physiological status of the turtles.

Stable isotopic comparison between loggerhead sea turtle tissues

RATIONALE Stable isotope analysis has been used extensively to provide ecological information about diet and foraging location of many species. The difference in isotopic composition between animal tissue and its diet, or the diet-tissue discrimination factor, varies with tissue type. Therefore, direct comparisons between isotopic values of tissues are inaccurate without an appropriate conversion factor. We focus on the loggerhead sea turtle (Caretta caretta), for which a variety of tissues have been used to examine diet, habitat use, and migratory origin through stable isotope analysis. We calculated tissue-to-tissue conversions between two commonly sampled tissues. METHODS Epidermis and scute (the keratin covering on the carapace) were sampled from 33 adult loggerheads nesting at two beaches in Florida (Casey Key and Canaveral National Seashore). Carbon and nitrogen stable isotope ratios were measured in the epidermis and the youngest portion of the scute tissue, which reflect the isotopic composition of the diet and habitat over similar time periods of the order of several months. RESULTS Significant linear relationships were observed between the δ(13)C and δ(15)N values of these two tissues, indicating they can be converted reliably. CONCLUSIONS Whereas both epidermis and scute samples are commonly sampled from nesting sea turtles to study trophic ecology and habitat use, the data from these studies have not been comparable without reliable tissue-to-tissue conversions. The equations provided here allow isotopic datasets using the two tissues to be combined in previously published and subsequent studies of sea turtle foraging ecology and migratory movement. In addition, we recommend that future isotopic comparisons between tissues of any organism utilize linear regressions to calculate tissue-to-tissue conversions.

Plasma biochemistry values in wild female hawksbill turtles (Eretmochelys imbricata), during nesting and foraging seasons in Qeshm Island, Persian Gulf

Normal reference ranges of biochemical parameters are considered important for assessing and monitoring the health status of sea turtles. For this study, plasma biochemistry determinations were analyzed in normal adult nesting and foraging hawksbill turtles (Eretmochelys imbricata). Blood samples were collected in March–April during (nesting season) and December–November (foraging season). Differences in plasma biochemistry values, except for creatinine and lipase, were statistically different (P < 0.05) between the two periods. Glucose, cholesterol, triglycerides, ALP (alkaline phosphates), AST (aspartate aminotransferase), bilirubin, total protein, LDH (lactate dehydrogenize), CK (creatine kinase), and amylase were significantly higher in nesting season than foraging season (P < 0.05). Whereas, urea, ALT (alanine aminotransferase), and albumin in the nesting season were significantly lower than during the foraging season (P < 0.05). It was concluded that the nesting E. imbricata showed significant variation in their biochemical profile due to reproductive output. This study has produced working reference intervals useful for hawksbill turtles for future conservation and rehabilitation projects in the Persian Gulf and may be of assistance in similar programs worldwide.