Sea Turtles in Changing Environments
Sea turtle populations have been depleted from historical levels due to human pressures including harvest and exploitation, fisheries by-catch, and habitat declines. Modern conservation efforts have done much to address these threats, but now a new suite of challenges associated with global environmental change are on the rise. In my research program with the Jumby Bay Hawksbill Project in Antigua, I study a various aspects of environmental change and how they impact hawksbill sea turtle ecology.
Macroalgae at nesting beaches —
Throughout the Caribbean, Sargassum macroalgae has been proliferating in unprecedented quantities and collecting in coastal nesting areas. The above picture illustrates the conditions on sections of our study beach on Long Island, Antigua for much of the 2015 nesting season. Macroalgae “shorings” have ramifications for both nesting adults and emerging hatchlings. We are involved in a project aimed to describe the effects of Sargassum in Antigua, and our efforts kicked off with a short paper published as a natural history note in Frontiers in Ecology and the Environment. We continue this work with original research to explore this issue more rigorously, and published some preliminary results in a conference paper.
Invasive species —
One feature of the environmental change occurring globally is an increase in species invasions. At our study beach on Long Island, Antigua, an invasive beach shrub (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.
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. The above graphic shows incubation temperatures for two nests that we 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 this pivotal temperature and does not become 100% female immediately. Beyond affecting sex ratios, extreme temperatures can lead to egg and hatchling mortality, so we document nest hatching success for these nests as well. Part of my PhD research asks: What environmental factors combine with atmospheric and sand temperatures to ultimately dictate hawksbill egg incubation temperatures, and how does this inform our understanding of climate change’s impacts on sea turtles?
Changes in regional foraging habitats (satellite tracking) —
In the above picture I am attaching a satellite transmitter to a hawksbill sea turtle with the help of the Jumby Bay Hawksbill Project field team in 2016. I am layering marine epoxy to glue it to the carapace. This is important work because while we have a detailed 30-year dataset describing hawksbill nesting ecology, our knowledge of their offshore movements is limited. They spend the vast majority of their lives in foraging habitats that we know almost nothing about! Knowing where they travel will enhance our ability to conserve the critically endangered species. Further, we hope to combine this work with stable isotope methodology and demographic analyses to start to determine if different foraging locations (and/or environmental change at these locations) lead to different dietary strategies (inferred from stable isotopes) and, in turn, influence reproductive output. See this migration map for an example of out what one of our turtles is up to.
In the Florida Keys, various endemic mammals are threatened by a myriad of anthropogenic and environmental factors. Dr. Michael Cove has a developed a research program that primarily uses camera trapping to pursue ecological questions regarding these endangered small mammals, with focus on the Key Largo Woodrat, Key Largo Cotton Mouse, Lower Keys Marsh Rabbit, and Florida Key Deer. To date, we have collaborated with others to publish four papers together from our work in the Keys (see Mike’s Google Scholar page for additional publications). One publication is a field note describing a possible range extension for a familiar reptile, a second paper in Restoration Ecology evaluates a Key Largo Woodrat habitat restoration strategy, the third publication documents a novel and peculiar mammal interaction, and the final paper is an “EcoPic” article in Frontiers in Ecology and the Environment that poses questions about woodrat “stick stacking” behavior. Stay posted for more work that addresses other questions in this fascinating ecosystem.
The Caribbean is host to an impressive example of adaptive radiation. Lizards in the genus Anolis inhabit islands throughout the region and have adapted to their local environments, resulting various cases of phenotypic divergence (i.e., developing different traits in different environments) and speciation.
In Antigua, we have two anole species: Watts’ anole (A. wattsi) and Leach’s anole (A. leachii). During our nocturnal sea turtle nesting surveys we were surprised to observe these typically diurnal (active during the day) lizards out and about, making the most of nocturnal foraging opportunities. We focused in on this behavior for a natural history study. I collaborated with Dr. Chris Thawley, Alex Fireman, Dr. Sean Giery, and Dr. James Stroud to publish a paper from this research project in the journal Herpetological Conservation and Biology— give the paper a read! James and I also published a short note documenting nocturnal behavior in the Watts’ anole for the first time.
The gene is increasingly becoming the fundamental unit of ecology. This is especially true for sea turtle ecology, where DNA preserves demographic patterns that would otherwise be unobservable and unknown because of the highly migratory and cryptic nature of sea turtle life histories. In recognition of this reality, I have focused much of my coursework and collaboration on conservation genetics. The best of example of this came in 2020, when I coauthored a paper in Oecologia titled “Gridlock and beltways: the genetic context of urban invasions.” This work represents an intersection of several of my interests, including movement ecology (i.e., landscape genetics), urban ecology, and invasive species biology. The paper was spearheaded by first author Emily Reed, an urban landscape genomicist in the Burford Reiskind Lab, with two other coauthors: Dr. Megan Serr and Dr. Martha Burford Reiskind. Part of Figure 1 from our review is shown here, but I encourage you to read it for yourself!