Sea turtles face substantial threats to their survival. Global warming, driven by human activities, presents a profound challenge to these creatures. The escalating temperatures of our planet are disrupting fundamental biological processes and altering the marine environments sea turtles rely upon. This environmental shift impacts various aspects of their life cycle, from reproduction to habitat and overall health.
Shifting Sex Ratios
Sea turtles exhibit temperature-dependent sex determination (TSD). The sex of a hatchling is determined by the sand temperature surrounding the eggs during incubation. Warmer nest temperatures produce a higher proportion of female hatchlings, while cooler temperatures result in more males. The “pivotal temperature,” yielding an equal ratio of males and females, is around 29 degrees Celsius (84.2 degrees Fahrenheit).
Rising global temperatures are warming nesting beaches, leading to a significant imbalance in sex ratios. On some northern Great Barrier Reef nesting beaches, nearly all green sea turtle hatchlings are now female. If average incubation temperatures exceed 31 degrees Celsius (87.8 degrees Fahrenheit), a nest can produce 100% female hatchlings. This “feminization” of sea turtle populations poses a serious long-term threat to their reproductive viability.
A heavily skewed sex ratio means a reduced number of males available for breeding. While one male can mate with multiple females, females may struggle to find mates, potentially leading to a decline in successful reproduction and genetic diversity. The long-term effects of this imbalance may not become fully apparent for decades, as sea turtles reach sexual maturity after 25 to 40 years.
Altered Habitats and Food Availability
Global warming directly impacts sea turtle habitats through rising sea levels and altered ocean conditions. Rising sea levels threaten vital nesting beaches. Even a modest rise, such as 0.5 meters, could lead to a substantial loss of beach nesting habitat, with some studies projecting a loss of up to a third of total beach area. This inundation of nesting sites can reduce nesting success rates and force females to lay eggs in higher-risk areas, increasing the likelihood of nests flooding during storms.
Ocean warming and acidification also affect crucial food sources for sea turtles. Warmer ocean temperatures can lead to coral bleaching, damaging coral reefs that serve as foraging grounds for species like hawksbill turtles. Ocean acidification, caused by the absorption of excess carbon dioxide, further degrades coral reefs by reducing the availability of calcium carbonate.
Similarly, seagrass beds, a primary food source for green turtles, are vulnerable to ocean warming and acidification. Increased temperatures and acidity can hinder seagrass growth and abundance, leading to food scarcity and nutritional stress. Changes in the distribution and abundance of prey species due to warming waters can force sea turtles to expend more energy to find food.
Changed Migration Patterns and Health Risks
Changing ocean temperatures and currents can significantly alter sea turtle migration routes and foraging grounds. Sea turtles rely on specific ocean currents as “highways” for their long-distance migrations, and shifts can force them to seek new areas or travel longer distances, increasing their energy expenditure and overall stress. For example, some loggerhead turtles have shifted their foraging ranges in response to changes in ocean temperatures and food distribution.
Warmer ocean temperatures can also increase the prevalence and severity of diseases within sea turtle populations. Fibropapillomatosis (FP), a debilitating disease characterized by tumors on the skin and internal organs, is a significant concern. While primarily associated with a herpesvirus (Chelonid herpesvirus 5), warmer water temperatures are suspected to play a role in its emergence and spread. Studies have observed that captive green turtles develop more tumors during warmer months, suggesting a link between environmental temperature and FP occurrence. This increased susceptibility to disease compromises the health and survival of sea turtle populations.