Article: Low-Cost Tools Mitigate Climate Change During Reproduction in an Endangered Marine Ectotherm by Clarke and colleagues (2021)
Background: Global surface temperatures are expected to increase from 3.7 to 4.8oC by 2100 (IPCC 2018). As we have discussed in previous article summaries (Bees; Corals; Marine Life), biodiversity loss is of great concern due to global climate change. Most mitigation efforts are aimed at conserving terrestrial species even though marine species are at risk of increased temperatures as well. Sea turtles, for example, face severe threats from increasing temperatures. The sex of sea turtles is indirectly determined by temperature during incubation; warmer temperatures lead to populations dominated by females. This imbalance decreases reproductive potential because it limits the number of breeding pairs. Beyond affecting sex, high temperatures can also prove lethal to entire clutches by preventing egg hatching. Marine turtles are also at risk of population loss due to plastic pollution, fishing, and poaching so relieving a major potential stressor, such as increased environmental temperatures, is even more critical to their survival. Therefore, Clarke and colleagues aimed at developing a cheap, simple mitigation strategy to reduce turtle nest incubation temperatures.
Methods: Clarke and colleagues tested their turtle-saving mitigation strategy in Boa Vista, Cape Verde, West Africa at the second largest nesting site of loggerhead sea turtles in the world. In 2012, sixty clutches of eggs (i.e., nests) were collected and divided into three treatment groups: (1) 20 clutches were reburied under shadowing material (i.e., clutch shading), (2) 20 clutches were split into two groups and reburied separately under normal conditions (i.e., clutch splitting), and (3) 20 clutches were reburied all together without any manipulation. Because individual eggs produce their own heat through metabolism, clutches with less eggs are thought to produce less heat than larger clutches. Treatments groups (2) and (3) were repeated in 2014. The temperatures of the clutches were monitored using temperature loggers at each clutch site, and the weight, length, and width of baby turtles (i.e., hatchlings) were measured immediately after hatching. Hatching success, as defined as the proportion of empty eggshells over the initial number of eggs, was calculated as well.
Findings: The control clutches (i.e., non-manipulated) had the highest average incubation temperature followed by (highest to lowest) split clutches and shaded clutches. Further, the incubation period of the control clutches was significantly shorter than the incubation periods of split and shaded clutches. Shaded clutches took the longest time to incubate (66 days). Clarke and colleagues found that more eggs in a clutch resulted in higher incubation temperatures. Hatchling size was similar among clutches of each treatment group, and hatching success was found to be significantly higher for split clutches than control clutches (only in 2014, however). In the control, split, and shaded treatment groups, the proportion of female hatchlings was 69%, 45%, and 1.5%, respectively.
Conclusions: As global temperatures continue to rise, mitigation strategies might be required to assist the survival of marine or terrestrial species. While more research is needed to determine if marine turtles are able to efficiently adapt to climate change and human disturbances, a proactive understanding of safe, effective, and cheap mitigation strategies is necessary. Clarke and colleagues found that hatching success was significantly higher for split clutches than normal clutches in 2014 but not in 2012. Although clutch temperatures were not examined in 2014, the gradual global temperature rise might have contributed to turtles eggs reaching their temperature limits. Thus, the knowledge of a strategy that reduces clutch temperatures, such as clutch splitting, is helpful for quick mitigation efforts in warmer years. Also, if temperatures extremely distort sex ratios by increasing the proportion of females, the shading stategy can effectively produce more males to compensate. Time and future research will tell us if clutch splitting or shading are needed to save the marine turtle population.
Figure: Map of study site: Boa Vista, Cape Verde, West Africa.
Reference:
Clarke, Leo J., et al. "Low‐cost tools mitigate climate change during reproduction in an endangered marine ectotherm." Journal of Applied Ecology (2021).
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