DOI: 10.5061/dryad.jdfn2z39f
title: Large-scale patterns of green turtle trophic ecology in the eastern Pacific Ocean

description: Trophic position and niche width are fundamental components of a species’
 ecology, reflecting resource use, and influencing key demographic
 parameters such as somatic growth, maturation, and survival. The present
 data file contains results of stable isotope analysis
 (stable-carbon, δ13C; stable-nitrogen, δ15N values) that was
 conducted on bulk skin tissue of 718 green sea turtles
 (Chelonia mydas) distributed among 16 foraging areas in the eastern
 Pacific from the US to Chile, a range spanning ~10,000 km. These study
 sites were distributed across a latitudinal range from
 33.736 °N to 23.098°S in the Eastern Pacific (Site Code): Long
 Beach, USA (LB); San Diego Bay, USA (SDB); north Gulf of Ulloa, Mexico
 (NGU); Magdalena Bay, Mexico (BMA); Los Angeles Bay, Mexico (BLA);
 Infiernillo Channel, Mexico (CIN); Navachiste Bay, Mexico (NAV); Dulce
 Gulf, Costa Rica (DUL); Cocos Island, Costa Rica (COC); Gorgona Island,
 Colombia (GOR); Punta Espinosa, Galapagos Islands, Ecuador (IGP); Bahia
 Elizabeth, Galapagos Islands, Ecuador (IGE); Caleta Derek, Galapagos
 Islands, Ecuador (IGD); oceanic waters, Peru (PPE); Pisco Paracas Bay,
 Peru (PAR); and Mejillones Bay, Chile (MEJ). Substantial
 variability in bulk tissue δ13C and δ15N values was
 found within and among sites. These data were also used to calculate the
 isotope niche space (used as a proxy for ecological niche space) using the
 Bayesian ellipse approach, and we found that isotope niche space varied
 among sites, likely influenced by the diversity of prey types and relative
 input of terrestrial- vs. marine-derived nutrients. In addition
 to providing additional spatial resolution for δ13C and
 δ15N isoscapes in the eastern Pacific, especially in coastal
 habitats, this study and resultant dataset further
 establish stable isotope analysis as an effective tool to study
 the trophic ecology of sea turtles across a variety of food webs and
 habitats. 
description: <em>Bulk skin tissue collection from green
 turtles</em> Turtle bulk skin tissues collected
 during field capture efforts thoughout the eastern Pacific Ocean.
  Epidermis (hereafter referred to as skin)<i> </i>was
 collected (ca. 0.10–0.25 g wet mass) from the dorsal neck or shoulder
 region of each turtle using a sterilized 6-mm biopsy punch or razor blade;
 the sampling location on the body was consistent at each study
 site. Samples were preserved in 2-ml cryovials filled with saturated salt
 solution, dry salt, or 70% ethanol solution and kept cool until transfer
 to the laboratory where they were stored at –20°C until
 analysis.  <i>Sample preparation for bulk tissue stable isotope analysis </i> Epidermal skin was separated from underlying dermis tissue when necessary using a razor blade. Skin samples were then rinsed with deionized water, finely diced, and freeze-dried at –50°C for 12 h in a lyophilizer (BenchTop K, VirTis, SP Industries, Gardiner, NY, USA). Lipids were removed from skin samples using a Soxhlet apparatus with a 1:1 solvent mixture of petroleum ether and ethyl ether for at least two 10-h cycles, or an accelerated solvent extractor (Model ASE300, Dionex, Bannockburn, IL, USA) with petroleum ether for three consecutive 5-min cycles of heating to 100°C at 1500 PSI pressurization. Following lipid extraction, the samples were freeze dried at –50°C for 3 h to remove any residual solvent. Sub-samples of prepared homogenized tissue were weighed (0.6–1.0 mg) with a microbalance and packed in tin capsules for mass spectrometric analysis. Primary producers were also freeze-dried prior to subsampling; however, lipid extraction was not performed prior to weighing (1.0–3.0 mg) and placement in tin capsules due to the extreme low lipid content of vegetative prey types (Harwood 2012). <i>Bulk tissue stable isotope analysis</i> Bulk tissue stable isotope analyses were conducted at the University of Florida, Gainesville, Florida USA. Elemental concentrations and stable isotope ratios were measured using an on-line C-N analyzer (Carlo Erba NA1500) coupled with an isotope ratio mass spectrometer (Thermo Electron Delta V Advantage), and followed well-established procedures (see Seminoff et al. 2012). All carbon isotopic results are expressed in standard delta notation relative to VPDB. All nitrogen isotopic results are expressed in standard delta notation relative to AIR. Sample stable isotope values relative to the isotope standard are expressed in the following conventional delta (δ) notation in parts per thousand (‰): δ = ([Rsample/Rstandard]-1)*(1000), where R<sub>sample</sub> and R<sub>standard</sub> are the corresponding values of heavy to light isotopes (e.g.<sup>15</sup>N/<sup>14</sup>N) in the sample and standard, respectively. All analytical runs included samples of a reference material with known δ<sup>13</sup>C and δ<sup>15</sup>N values (USGS40 and USGS41 from the USGS) inserted every 6 to 7 samples to calibrate the system and compensate for drift over time. Hundreds of replicate assays of reference materials indicated maximum measurement errors of 0.06‰ and 0.12‰ for carbon and nitrogen, respectively. The elemental concentrations of carbon (acceptable δ<sup>13</sup>C range = 25–60‰) and nitrogen ratio (acceptable δ<sup>15</sup>N range = 6–20 ‰) were used as quality assurance to assess stable isotope values before quantitative analyses; samples were excluded from analyses if they did not meet these criteria. The mean % C and mean % N for the retained samples was 41.1 ± 6.0 % and 13.0 ± 2.2 %, respectively (n = 718). The mean C:N ratio (mol/mol) for turtles at each study site was from 2.8 to 4.0. 
description: This dataset includes the following fields: 
 <em>Site Code: </em>the study was conducted at 16
 different sites in the eastern Pacific Ocean (See abstract for list of
 codes)<br> <em>Location: </em>the unabbreviated name of
 each of the 16 study sites<br> <em>LABID:
 </em> Numerical identifier for the particular turtle / sample that
 was housed in the tissue archive at NOAA - Southwest Fisheries Science
 Center prior to analysis<br> <em>Collection Date:
  </em>Calendar date that the turtle skin tissue sample was
 collected<br> <em>Run Date: </em> Calendar date that the
 skin tissue sample was analyzed via mass spectrometry <br>
 <em>Percent N: </em> Elemental concentration of nitrogen
 content by % weight within the tissue sample<br> <em>Percent
 C:  </em>Elemental concentration of carbon content by % weight
 within the tissue sample<br> <em>d15N:</em>  Stable
 nitrogen isotope value (per mil) for collected bulk skin sample<br>
 <em>d13C: </em> Stable carbon isotope value (per mil) for
 collected bulk skin sample<br> <em>SCL: </em>Straight
 carapace length (cm) of turtle from which sample was collected.  Note that
 not all turtles had SCL collected<br> <em>CCL:
 </em>Curved carapace length (cm) of turtle from which sample was
 collected.  Note that not all turtles had CCL collected <br>
 <em>C:N: </em>Termed the 'C-to-N-ratio', this is the
 ratio of the elemental concentrations recoreded in previous data fields of
 this spreadsheet (see above)<br> <em>Notes: </em> This
 field inlcuded any additional pertinent information for the bulk skin
 tissue sample.  Usage:  The data herein are raw
 empirical measurements of bulk tissue stable isotope values and turtle
 sizes. With these data any user should be able to calculate mean stable
 isotope values and sizes of turtles at each site as well as determine the
 relationship between these measurements for each site.