Finding a sea turtle to study isn’t as simple as walking onto a beach. Researchers can spend hours scouring foraging areas or strolling nesting beaches into the early morning waiting for turtles to appear.
When preparing to track sea turtles via satellite, finding the animal is just the beginning of the process; it can take another hour or two to load the transmitter onto the turtle. But when UF Associate Professor of Biology Hannah Vander Zanden uses stable isotope tracing, a couple minutes are enough to uncover a turtle’s history.
Vander Zanden, who is also the director of the Archie Carr Center for Sea Turtle Research, specializes in stable isotope tracing. The method reveals an animal’s history by analyzing the elements inside its body.
Stable isotopes are atoms of the same element that share the same number of protons but differ in their number of neutrons. They do not decay or change over time. The only difference between the atoms is their mass.
As an animal eats and drinks, stable isotopes integrate with its body revealing clues about diet and movement over time. In Vander Zanden’s research, discovering details about an animal’s diet and migratory route helps tell its story. All she needs is a sample, like a piece of its shell or a drop of its blood.
Animals reflect the local rainwater signal at the place their tissues were grown. Those found with heavy isotopes of hydrogen and oxygen are likely to have come from closer to the equator, where heavy isotopes rain down. Animals found with lighter isotopes come from closer to the poles. To determine more specific locations, the new sample data can be compared to existing datasets that chart the patterns of these isotopes.
“To me, it’s a really cool way to try to find out mysteries about animals that occurred before you encountered them,” Vander Zanden said.
Once a sample is collected, it makes its way to the lab and eventually, a mass spectrometer.
At UF, the Department of Geological Sciences Light Stable Isotope Mass Spectrometry Laboratory has four running mass spectrometers that Senior Associate in Geochemistry Jason Curtis uses to analyze samples. Curtis said the lab provides chemical and isotopic information about carbon, nitrogen, hydrogen and oxygen and the isotopes in a wide range of materials.
Mass spectrometers evaluate samples like pieces of shell, fur, hair, tissue, leaves, pieces of rock and even insects. To analyze the material, it is measured using a microbalance, placed in a tin capsule, compacted and loaded into an elemental analyzer.
While in the machine, the capsule is burned at 1,000 degrees Celsius, turning the sample into gas. The gas travels through a second oven at 650 degrees Celsius that eliminates extra oxygen, then into a tube with a chemical that gets rid of water and into another oven at a lower temperature with a gas chromatographic column and a detector that help reveal nitrogen and carbon levels.
The gas then goes through an interface that reduces the pressure of the gas before it is fed into the mass spectrometer that measures the isotopes.
Curtis, who manages the lab, receives samples from throughout the university, across the state, and even outside of the country.
“This department of geology is well known for our facilities,” Curtis said. “Not just stable isotopes but heavy isotopes, like lead isotopes, strontium isotopes, argon. For the size of this department, we’re really well known.”
While this technique isn’t perfect, it has key benefits over other tracking methods.
Satellite tracking can provide very accurate locations of an animal’s migratory route and other types of data such as dive patterns, but a satellite transmitter can cost up to $5,000. A stable isotope sample? About $10.
Satellite transmitters also may be too big to place on some organisms. So other researchers may opt to use light-level geolocators, a more affordable way to determine an animal’s latitude and longitude. But when using those sensors, the animal needs to be re-encountered because the data is stored on the device.
Stable isotope analysis needs just one interaction with an animal. The method also makes it easier to research large groups of animals at once, painting a fuller understanding of population trends.
Vander Zanden’s research extends past just sea turtles. This approach has helped her learn about birds, bats, dolphins and more. The method doesn’t even require that the animal is still alive to learn about its past.
“There’s no way to put a tracker on a dead organism,” Vander Zanden said. “We can re-create history from an animal that otherwise couldn’t tell us something.”
How Scientists Collect Leatherback Sea Turtle Samples During Nesting Season
Hannah Vander Zanden and Archie Carr Center for Sea Turtle Research doctoral student Ariadna Arnau took samples from leatherback turtles during their nesting season this summer.
