by Anna Alquitela
Much research has been conducted on phenological reproductive responses to climate change. These responses occur commonly in plants, butterflies, birds, amphibians, fish, and insect larvae. Because sea turtles use thermal cues to begin migration to nesting sites, the authors hypothesized that leatherback turtles (Dermochelys coriacea) are delaying nesting in response to increased temperatures at their foraging grounds (Neeman et al. 2015). Biological responses due to increased temperatures have been observed in many other species of sea turtles. Some of these effects include offset sex ratios in embryos, nesting scarcity, reduced clutch size, and increased mortality rates of eggs and hatchlings.
Data were collected at the foraging and nesting sites of two beaches (Playa Grande and Tortuguero) in Costa Rica and one beach (Sandy Point) in St. Croix, US Virgin Islands over the course of nine seasons between 1983 and 2010. The data included observations of turtle tracks at nesting sites and average temperatures at foraging sites. Statistical analyses were performed for each nesting site, correlating the 5th and 10th percentile dates to the respective foraging site temperatures. Of 72 comparisons between nesting dates and temperatures, only 10 correlations were significant, and of the 20 correlations between nesting dates and seasonal timing of temperatures, only one was significant. The authors admit that “migratory cues are complex,” but found that sea turtles are not responding to “changes in seasonality at the foraging grounds.” It is feasible that global climate change is not affecting the reproductive success of leatherback turtles. Nevertheless, the IUCN Red List of Endangered Species lists leatherback turtles as vulnerable because they often mistake plastic bags that end up in the ocean for jellyfish, their favorite prey, and eating plastic bags is damaging or fatal to them.
Neeman, N., Robinson, N. J., Paladino, F. V., Spotila, J. R., O’Connor, M. P. 2015. Phenology shifts in leatherback turtles (Dermochelys coriacea) due to changes in sea surface temperature. Journal of Experimental Marine Biology and Ecology 462, 113-120.