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.
Through my current postdoctoral research with the Marine Turtle Ecology and Assessment Program at NOAA’s Southwest Fisheries Science Center, I aim to advance our capacity to conserve sea turtles in a changing world. I am working to find new ways to integrate data from stable isotope analysis, satellite telemetry, and longterm mark recapture. Combining this information will help to to address fundamental questions in sea turtle biology, such as foraging distributions and the drivers of population dynamics. Stay tuned for more specifics!
In my doctoral research program with the Jumby Bay Hawksbill Project in Antigua, I studied a various aspects of environmental change and how they impact hawksbill sea turtle ecology. See below for more! I received my PhD in summer 2021, but much of this work continues today.
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 a formal analysis of Sargassum’s effects on spatial nesting patterns with a journal article in Climate Change 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.
Changes in migratory and foraging habitats (satellite tracking) —
Environmental change is playing out in all sea turtle habitats, not just nesting beaches. The first step toward understanding changes in key marine habitats is to determine where turtles migrate to (i.e., their home foraging area), and we do this using satellite transmitters. In the above picture I am using epoxy to attach a transmitter to a hawksbill with the help of the Jumby Bay Hawksbill Project field team in 2016. See this migration map for an example of the migratory movements of one of our turtles.