Research Projects & Collaborations

Conserving sea turtles in a changing world

Sea turtle populations were drastically depleted from historical (pre-Columbian) levels due to human pressures including harvest, fisheries by-catch, and habitat destruction. While modern conservation efforts have made headway against many of these human threats, global environmental change is posing a new suite of rising challenges. Through my current postdoctoral research with the Marine Turtle Ecology and Assessment Program at NOAA’s Southwest Fisheries Science Center (La Jolla, California), as well as in my past work as an NSF Graduate Research Fellow and Fulbright Fellow as I pursued my PhD in the Burford Reiskind Lab at NC State University, I have sought to support sea turtle conservation and population recovery in the context of global change

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 biotelemetry, GIS, and spatial modeling to generate this key information.

Satellite telemetry —

Attachment of a satellite transmitter onto a hawksbill sea turtle in Antigua, West Indies

Sea turtles are highly mobile and migratory species that are relatively difficult to observe in marine environments. Yet, to support the recovery of imperiled populations, we need to know where they occur and how they move through managed waters. I use satellite telemetry to get at this 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 to its foraging area—see this map, this paper, or this paper for examples and further information on migrations from Antigua (Eastern Caribbean).

Animal-borne biologgers —

Suction cupping the CATS camera

Beyond satellite transmitters, I use other types of animal-borne sensors to generate information on three dimensional movement and energy use. Here, you can see my mentee and collaborator Cameron Mullaney and me using suction cups to attach a multi-sensor, animal-borne pop-off camera to a foraging green turtle in Southern California (in this case attached alongside a GPS transmitter). This camera, manufactured by Customized Animal Tracking Solutions (CATS), allows us to observe what turtles eat, shows us how they behave within their immediate local environment, and provides a huge amount of complementary sensor data (e.g., depth, temperature, accelerometry).

Cameron Mullaney alongside a green turtle equipped with the CATS camera

We are gaining a unique, fine-scale look at the daily lives of California green turtles. One initial finding: green turtles in San Diego Bay are quite social! You can see some evidence of this via the photo below. (All of this research was permitted under NOAA permit #18238).

Two green turtles interacting in San Diego Bay, as captured via the CATS pop-off camera

Global change

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. A major goal of my research is to improve our understanding of how these thermal effects on offspring will translate to effects on population dynamics. For example, I led a review on these subjects in the journal BioScience.

Incubation temperatures within two hawksbill sea turtle egg clutches

I have also led projects examining 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 temperatures during the thermosensitive period—when the sex of embryos 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, for example, change to 100% female immediately). Beyond affecting sex ratios, extreme temperatures can lead to egg mortality, so we documented nest hatching success as well. My ongoing research asks: 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?

Macroalgae blooms

Mass Sargassum arrival in Antigua, West Indies

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 conditions at our study site on Long Island, Antigua for much of the 2015 nesting season. Sargassum accumulation has ramifications for both nesting adults and emerging hatchlings. I led projects aimed at describing the effects of Sargassum in Antigua, starting with a short natural history paper 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 more refined analyses of Sargassum’s effects on nesting: a 2021 article in Climate Change Ecology and a 2022 article in Journal of Experimental Marine Biology and Ecology.

Other research areas in marine ecology

Stable isotope ecology —

Carbon-nitrogen biplot exemplifying isotopic differentiation of species groups. Figure taken from Burgett et al. 2018.

You are what you eat! Ecologists leverage this relationship by using stable isotopes as ecological tracers (more on this below). In my postdoctoral position I am working with global leaders in sea turtle stable isotope ecology to employ isotopes as spatial tracers (i.e., to infer where animals move to/from).

Isotopes of a given element are very 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, distinct sources will differentially, and consistently, incorporate more or less of the heavy and light isotope (many times creating a unique signature, or ratio, for the source). For instance, a seagrass species at a given location will have a fairly consistent ratio of 13C:12C (aka δ13C), and this ratio should be distinct from an algae species in the same area. Animals that eat these food sources will incorporate the carbon ratios into their tissues, informing our estimates of 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.