Costa, L. L., Bulhões, E. M. R., Caetano, J. P. A., Arueira, V. F., de Almeida, D. T., Vieira, T. B., Cardoso, L. J. T., & Zalmon, I. R. (2023). Do coastal erosion and urban development threaten loggerhead sea turtle nesting? Implications for sandy beach management. Frontiers in Marine Science, 10. https://doi.org/10.3389/fmars.2023.1242903
Sea turtle hatchlings. Image source: Florida Fish and Wildlife via Flickr Creative Commons
A Day in the Life
A sea turtle’s life consists of three main tasks: migrating (moving from one home to another), foraging (looking for food), and nesting (laying eggs). But how does it know where to go and when to complete each of these tasks? And how might human actions affect the success of these life stages?
Choosing Their Home
When nesting season comes around, sea turtles rely on the earth’s magnetic field to navigate long distances, and on local signals, such as beach conditions, to find a suitable nesting area on the beach. Typically, females return to their natal beaches (where they were born) to lay the next generation of turtles. The selection of these nesting sites is crucial to the new turtles, whose mothers return to the ocean after laying eggs and can therefore provide no care or protection. In order to increase the chances of their offspring’s survival, female sea turtles tend to lay eggs in areas with sparse vegetation to protect them from plant roots and predators, and mid-beach spots with higher elevation to prevent flooding.
However, other factors that contribute to site selection are not well studied, and this study aimed to determine whether human changes to the coastline, including erosion and urban development, negatively impact sea turtle nesting.
Rio de Janeiro Beach. Image source: Dmitry B. via Flickr Creative Commons
The study area included the turtle nesting sites in north Rio de Janeiro, Brazil, where the construction of a port in 2007 brought many urban changes to the site. The unique morphology of the beach in that area naturally makes it vulnerable to erosion, and the construction of the port, dams, and other man-made structures increases that vulnerability.
In the study, researchers identified and marked turtle crawl sites throughout the 2022-2023 nesting season, then measured erosion rates and urbanization to determine whether sites selected by loggerhead sea turtles for nesting had eroded.
The results of this study showed a correlation between beach erosion rate and turtle nesting site selection. The higher the erosion rate in an area, the less likely it was to be a location of a nest, and the less likely for a false turtle crawl to occur, an event in which the turtle returns to the water without laying a nest.
Where Do Humans Come In? The Positives and the Negatives
These results suggest that loggerheads tend to choose beaches that aren’t eroded, and since females tend to return to their own natal sites to nest, this might represent a trend in diminishing use of eroded sites in the past as well. Additionally, because false crawl frequency was higher in areas with less erosion, it is likely that turtles do not emerge at all in the eroded sites, as they can determine early on that they are not suitable areas for nesting. Even more concerning, fewer loggerhead nests were found and false crawls were more frequent in areas of higher urbanization.
On a positive note, there are many avenues through which beach management can mitigate these problems. For one, pumping sand from the river to compensate for the erosion at the beach is a great nature-based solution. Renourishing beaches to make them more suitable for nesting is another potential solution but can be more complicated because it could introduce exotic species and change the natural landscape. Another more simple solution would be to move already laid eggs to more stable beaches.
Further investigation into other conditions that contribute to hatching success, both natural and anthropogenic, would benefit the implementation of the aforementioned solutions and help save the turtles.
Cover photo by Dawn Childs on Picryl
I am an MPS student at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Sciences pursuing a degree in Marine Biology and Ecology on the Tropical Marine Ecosystem Management Track. After graduating, I plan to use my education and experience to pursue a career in science writing or film production to help communicate the importance of the ocean to the general public.