Adaptation of sea turtles to climate warming: Will phenological responses be sufficient to counteract changes in reproductive output?

Abstract

Sea turtles are vulnerable to climate change since their reproductive output is influenced by incubating temperatures, with warmer temperatures causing lower hatching success and increased feminization of embryos. Their ability to cope with projected increases in ambient temperatures will depend on their capacity to adapt to shifts in climatic regimes. Here, we assessed the extent to which phenological shifts could mitigate impacts from increases in ambient temperatures (from 1.5 to 3°C in air temperatures and from 1.4 to 2.3°C in sea surface temperatures by 2100 at our sites) on four species of sea turtles, under a “middle of the road” scenario (SSP2‐4.5). Sand temperatures at sea turtle nesting sites are projected to increase from 0.58 to 4.17°C by 2100 and expected shifts in nesting of 26–43 days earlier will not be sufficient to maintain current incubation temperatures at 7 (29%) of our sites, hatching success rates at 10 (42%) of our sites, with current trends in hatchling sex ratio being able to be maintained at half of the sites. We also calculated the phenological shifts that would be required (both backward for an earlier shift in nesting and forward for a later shift) to keep up with present‐day incubation temperatures, hatching success rates, and sex ratios. The required shifts backward in nesting for incubation temperatures ranged from −20 to −191 days, whereas the required shifts forward ranged from +54 to +180 days. However, for half of the sites, no matter the shift the median incubation temperature will always be warmer than the 75th percentile of current ranges. Given that phenological shifts will not be able to ameliorate predicted changes in temperature, hatching success and sex ratio at most sites, turtles may need to use other adaptive responses and/or there is the need to enhance sea turtle resilience to climate warming.

Spatial and life history variation in a trait-based species vulnerability and impact model

“…Carry-over effects may occur from as early as the egg stage in turtles [28]. For example, warming incubation temperatures of sea turtle eggs can impact individual behaviour, physiology, morphology, and performance, and may have long-term impacts on sex ratios resulting in reduced species or population fitness [68][69][70]. Although our model does not quantitatively consider carry-over effects across life stages, it does provide valuable insight into which life stages are vulnerable to specific stressors.…”

Influence of incubation temperature, maternal effects, and paternity on quality of olive ridley hatchlings (Lepidochelys olivacea) from a mass‐nesting beach in the Mexican Pacific

“…Sand temperatures at sea turtle nesting sites are projected to increase from 0.58°C to 4.17°C by 2100 (Fuentes et al, 2024), and this is expected to affect the primary sex ratio, hatchling success, morphology, and locomotor performance of hatchlings from various sea turtle species. Sea turtles have existed for millions of years and have witnessed several climate change events; however, we do not know how these species might be affected by these projected rapid changes.…”

“…First, successful incubation is only possible within certain thermal limits; in this sense, an incubation temperature ranging between 25°C and 35°C ensures the success of sea turtle egg incubation (Fuentes et al, 2024), beyond this threshold, there is likely to be lower hatching success and higher rates of morphological abnormalities (Fuentes et al, 2024;Howard et al, 2014). Second, the differential effect of temperature during the incubation period can impact the primary sex ratio, survival rate, duration of the incubation period, yolk conversion to tissue, hatchling's body condition, post-hatch growth, and locomotor performance (Booth, 2017;Fleming et al, 2020;Mueller et al, 2019).…”

“…However, under most future climate scenarios, it is likely that natural incubation conditions will change dramatically due to increased air and sea temperatures, sea-level rise, changes in rain patterns, and the frequency and intensity of storms (Patrício et al, 2019). Several studies suggest that sea turtles respond to climate change through various mechanisms, including range shifts to more climatically suitable environments, and alternatively, they may exhibit phenotypic plasticity, allowing the organisms to modify their morphology, physiology, or behavior to compensate for changes in the environment (Fuentes et al, 2024;Hulin et al, 2009;Waldvogel et al, 2020). In the long-term, it could cause adaptive changes that may include changes in pivotal temperature or adjustments in the choice and timing of nesting (Fuentes et al, 2024;Georges, 2013;Jensen et al, 2018).…”