Conserving sea turtles in a changing world
Sea turtle populations have been depleted from historical levels due to human pressures including harvest, fisheries by-catch, and habitat destruction. While modern conservation efforts have made headway against many historical threats, global environmental change is posing a new suite of rising challenges.
In my current postdoctoral research with the Marine Turtle Ecology and Assessment Program at NOAA’s Southwest Fisheries Science Center (San Diego, CA), I am building capacity to conserve sea turtles in the East Pacific, where my primary focus is the green turtle (Chelonia mydas). I am conducting projects that use animal biotelemetry and stable isotopes to reveal important patterns in movement, habitat selection, and energy use.
During my PhD research program with the Jumby Bay Hawksbill Project in Antigua, West Indies, I studied a nesting population of hawksbill sea turtles (Eretmochelys imbricata). My projects focused on migratory ecology and global change biology. I received my PhD in summer 2021, but much of this work continues today. See below for more!
Animal biotelemetry —
Conservation, at a very fundamental level, depends on information showing where animals occur, what types of habitats they use, and how they move within said habitats. I use animal biotelemetry to produce this key information. In the above picture I am using epoxy to attach a satellite transmitter to a nesting hawksbill turtle with the help of Jumby Bay Hawksbill Project field researchers. We then tracked its post-reproductive migration back to its foraging area—see this map for an example migration. Beyond satellite transmitters, I also use other types of animal-borne sensors to generate information on three dimensional movement and energy use.
Stable isotope ecology —
You are what you eat! Ecologists leverage this relationship by using stable isotopes as ecological tracers (more on this below). In my postdoctoral work I am working with global leaders in sea turtle stable isotope ecology, and I am focusing on using stable isotopes as a spatial tracer (i.e., to infer where animals move to/from). Stay tuned for more specifics as this research unfolds. (Figure taken from Burgett et al. 2018).
Isotopes of a given element are extremely similar, containing the same amount of protons but differing in the number of neutrons. For example, with carbon we typically focus on the stable 13C and 12C isotopes, where 13C is heavier by one neutron. Stable isotopes of any element remain unchanged (i.e., do not decay) as they transition through sources and structures in nature, and what makes them especially useful is that different sources have unique rates of discrimination against heavy isotopes. In other words, different sources will incorporate more or less of the heavy versus light isotope. For instance, a seagrass species at a given location will have a fairly consistent ratio of 13C:12C (aka δ13C), and this ratio will be distinct from an algae species in the same area. Animals that eat these food sources will incorporate the carbon ratios into their tissues, allowing us to estimate/infer what they feed on. In this way, the ratio of heavy to light stable isotopes can be used to trace the flow of energy through food webs.
Macroalgae at nesting beaches —
Global change has featured an increase in algae blooms. Throughout the Caribbean, Sargassum macroalgae has been proliferating in unprecedented quantities and collecting in coastal nesting areas. The above picture illustrates the conditions at our study site on Long Island, Antigua for much of the 2015 nesting season. Macroalgae accumulation has ramifications for both nesting adults and emerging hatchlings. I am involved in projects aimed to describe the effects of Sargassum in Antigua, and my efforts with collaborators kicked off with a short paper published as a natural history note in Frontiers in Ecology and the Environment. We followed up this note with more rigorous original research, presenting preliminary results in a conference paper and later publishing two formal analyses of Sargassum’s effects on nesting: a 2021 journal article in Climate Change Ecology and a 2022 article in Journal of Experimental Marine Biology and Ecology.
Rising temperatures —
Atmospheric temperatures have been rising at a rapid rate. This has major implications for sea turtles that exhibit temperature-dependent sex determination (TSD), where warmer temperatures lead to the production of more female hatchlings. High temperatures can also reduce survival of incubating embryos. Understanding how these thermal effects on offspring will translate to effects on population dynamics is complex, and I led a review with several other collaborators on these subjects that was published in BioScience in 2021 (the first chapter of my dissertation).
I have also led a project studying incubation temperatures in the field to understand the effects of warming temperatures on the Antiguan hawksbill population. The above graphic shows temperatures in two nests (green and blue lines) monitored with data loggers in 2015. We can examine where temperatures were during the thermosensitive period for TSD (when sex is determined) and how this compares to the pivotal temperature that creates a 50/50 sex ratio. (Note that this ratio tapers in either direction from the pivotal temperature and does not become 100% female immediately). Beyond affecting sex ratios, extreme temperatures can lead to egg mortality, so we documented nest hatching success for these nests as well. My PhD research asked: What environmental factors combine with atmospheric and sand temperatures to ultimately dictate hawksbill egg incubation temperatures, and what are the implications for sex ratios, hatching success, and population dynamics?
Invasive species —
Another feature of the environmental change occurring globally is an increase in species invasions. At our study beach on Long Island, Antigua, an invasive beach plant (Scaevola taccada, pictured left) has become the dominant species of vegetation and differs significantly from the previous dominant native plant, seagrape (right). We are in the midst of a project that seeks to describe how hawksbills are interacting with this invasive plant and the resulting impacts on nesting ecology.