Figure 1: Photo of sea turtle. (Courtesy of Cindy Spence of University of Florida)
As global temperatures continue to increase du to climate change, populations of sea turtles are on the decline. Sea turtles are considered an ambassador flagship species that helps draw the society’s attention to help conserve them since they are on the brink of extinction. The concern for the future of sea turtles is more important than ever as the global climate continues to rise.
Sea turtles are ectotherms with temperature-dependent sex determination. This means that the outcome of the eggs produced by sea turtles is dependent on the temperature of the sand in which the female turtles lay their eggs in. Studies have found that the temperatures of the sand that green sea turtles lay their eggs on affects the sex of the offspring and if not at an optimal temperature could mess up the sex ratio of offspring (Tomillo and Spotila 2020). Warmer sand temperatures have been found to produce females and cooler sand temperatures produce males. If the temperature of the sand is continuing to rise then we will continually see clutches with only female offspring which is an issue because with no males in the population the sea turtles will not be able to continue to reproduce. There have been studies done using incubation to study the effects of the temperature on the sex of the eggs and the mortality rates of the eggs in incubation to study possible management processes to help stop the declining population of sea turtles and to hopefully learn more about the future thermal tolerance of sea turtles (Booth 2017; Laloë et al. 2017).
Figure 2: Baby sea turtles. (Courtesy of Cindy Spence of University of Florida)
Sea turtles also face the challenge of decreasing food availability. This decrease in food availability traces back to the increasing climate because the increase is affecting the coral that sea turtles depend on for food. With coral populations declining and dying, the sea turtles food supply gets lower and lower. The decreasing food supply for sea turtles has led to more time in between nesting periods since the turtles do not have the energy needed to reproduce and provide for the embryos. A study done by Stubbs et al. used a model to predict a continued increase in time between nesting periods for female sea turtles in situations with decreasing food availability (2020). With more time in between nesting there is less reproduction of sea turtles happening which makes the whole population begin to decline.
There is still more research needed to fully understand the future of sea turtle populations but the increasing climate is not predicted to decrease any time in the near future so the sea turtles are under a lot of pressure. With increased frequency of marine heatwaves reducing reproductive output and decreasing food availability, the reproductive output of eggs produced is on the decline along with the sex ratio of the eggs becoming mostly if not all female. Future research could look into the thermal tolerance of sea turtles and the thermal tolerance of the offspring to see if sea turtles could become more tolerant to these increasing temperatures. Along with this, more research needs to be done to understand the future of the food availability of sea turtles to be able to have the energy and resources needed to reproduce successfully.
References:
Booth DT (2017). Influence of incubation temperature on sea turtle hatchling quality. Integrative Zoology. https://onlinelibrary.wiley.com/doi/abs/10.1111/1749-4877.12255
Laloë JO, Cozens J, Renom B, Taxonera A, and Hays GC (2017). Climate change and temperature-linked hatchling mortality at a globally important sea turtle nesting site. Global Change Biology. https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13765
Spence C (2019). Sea Turtles Without Borders. Explore
Stubes JL, Marn N, Vanderklift MA, Fossette S, and Mitchell NJ (2020). Simulated growth and reproduction of green turtles (Chelonia mydas) under climate change and marine heatwave scenarios. Science Direct. 431. https://doi.org/10.1016/j.ecolmodel.2020.109185
Tomillo PS and Spotila JR (2020). Temperature-Dependent Sex Determination in Sea Turtles in the Context of Climate Change: Uncovering the Adaptive Significance. BioEssays. https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.202000146