The Ramirez Lab
Sea Movement Ecology & Resource Shifts
When isotopic or elemental differences exist among resources (habitat and/or diet) utilized by animals, this natural variation can be used to study animal migrations. Through complementary skeletal and geochemical analyses, I have harnessed this variation to provide novel insights to the oceanic stage duration and timing of oceanic-to-neritic ontogenetic habitat shifts in loggerhead, Kemp's ridley, and hawksbill sea turtles. When paired with complementary somatic growth rate information contained within their bones, such information has also allowed me to characterize growth dynamics surrounding these habitat shifts and, in some cases, to test ontogenetic niche theory. More recently, I have worked in collaboration with Drs. Alyssa Shiel (OSU) and Jessica Miller (OSU) to develop lead (Pb) isotope and trace element tools to study the connectivity of population subgroups within nearshore habitats. I am actively developing these and other geochemical techniques to enhance the tools available to study the movement of marine megafauna.
Sea Turtle Growth Dynamics
Sea turtle growth rates are highly variable within and among species, populations, and life stages. Yet, little is known about the specific factors underpinning this variability given the difficulty of studying growth rates in such highly mobile species. This limitation can be overcome through the study of their humerus bones (pictured right), which have been collected from dead, stranded turtles for decades and contain annual growth layers that record information on body size, age, growth, diet, and habitat use. Using skeletochronology I have characterized the ontogenetic and spatiotemporal growth patterns of loggerhead and Kemp's ridley sea turtles. I have also examined the influence of both natural (climate change, changing population density, diet composition) and anthropogenic stressors (Deepwater Horizon oil spill) on sea turtle growth rates, in some cases through complementary isotopic analyses. As sea turtle population dynamics are highly sensitive to small changes in demographic rates, characterizing the proximate drivers of somatic growth variation and subsequent influences on population dynamics is of high importance to sea turtle conservation and management.