Sea turtles are ancient reptiles that have navigated the world’s oceans for over 100 million years, but they now face unprecedented threats from rapidly changing global conditions. Their complex life cycle, spanning both terrestrial beaches and the vast marine ecosystem, exposes them to the broad consequences of climate change. The primary drivers—rising air and ocean temperatures, and increasing sea levels—directly interfere with the biological and physical processes necessary for survival. These interconnected impacts affect their reproduction, habitat, foraging, and overall health. Understanding the specific mechanisms by which a warming world impacts these vulnerable species is necessary for effective conservation.
Skewed Sex Ratios and Reproductive Failure
A profound consequence of rising global temperatures is the severe skewing of sea turtle sex ratios, rooted in their unique reproductive biology. Unlike mammals, the sex of hatchlings is determined by the temperature of the sand during the middle third of the incubation period, a process known as Temperature-Dependent Sex Determination (TSD). Warmer incubation temperatures produce females, while cooler temperatures result in males, with a narrow range of a few degrees determining the outcome. The specific temperature that yields a 50/50 ratio, known as the pivotal temperature, is generally around 29 degrees Celsius (84.2 degrees Fahrenheit) for many species, though this varies between populations.
Sand temperatures consistently above this pivotal point lead to a highly female-biased population, often termed “feminization.” Researchers have documented this disproportionate ratio in some nesting colonies, such as green sea turtles in the northern Great Barrier Reef, where up to 99% of juvenile turtles are female. This extreme imbalance creates a severe demographic crisis because the population will eventually lack enough males to successfully fertilize the abundance of females.
A sustained lack of new male recruitment over time threatens the long-term viability and decreases the genetic diversity of the species. Furthermore, if sand temperatures exceed the upper thermal limit for egg incubation, often around 34 degrees Celsius, the entire clutch can fail, resulting in total reproductive loss.
Physical Loss of Nesting Beaches
The coastal habitats sea turtles rely on for nesting are being physically diminished by a warming climate and rising sea levels. Sea level rise causes permanent inundation of lower-lying sandy beaches, directly reducing the available space for females to lay nests. Since female turtles exhibit high fidelity to their natal beaches, this loss can force them to nest in less optimal areas closer to the water.
Increased storm intensity, including hurricanes and tropical cyclones, further exacerbates this loss by causing severe erosion and powerful storm surges. These events wash away entire sections of beach and destroy nests, leading to the mortality of eggs and hatchlings.
In areas where human development has built infrastructure close to the shoreline, a dynamic called “coastal squeeze” occurs, preventing the natural landward migration of beaches as sea levels rise. This constriction traps the nesting habitat between the rising ocean and fixed human structures, ensuring the permanent loss of critical nesting zones.
Disruption of Marine Foraging Grounds
Oceanic changes directly impact the marine phase of the sea turtle life cycle by altering the distribution and nutritional quality of their food sources. Rising sea surface temperatures (SST) are changing the distribution of prey species, forcing turtles to undertake longer and more energetically costly migrations to find suitable foraging grounds. For example, the primary prey of leatherback sea turtles, gelatinous zooplankton, are shifting their range northward in response to warmer SST, compelling leatherbacks to follow them.
Ocean warming also affects the nutritional quality of the food available to herbivorous species, like the green sea turtle, which feeds primarily on seagrass. Studies show that green turtles feeding on a preferred seagrass diet exhibit significantly higher growth rates compared to those consuming algae or invertebrates. Seagrass meadows are increasingly threatened by ocean heatwaves and increased grazing pressure as other herbivores expand their range poleward.
Ocean acidification, caused by the absorption of excess atmospheric carbon dioxide, weakens the calcium carbonate structures of foundational ecosystems, leading to the degradation and bleaching of coral reefs. This decline directly impacts the hawksbill sea turtle, a species that relies heavily on coral reefs for its prey, such as sponges and other invertebrates. The combined effect of these changes is a reduction in the abundance and quality of food, leading to nutritional stress and lower reproductive output across various sea turtle species.
Increased Susceptibility to Disease
Warmer ocean temperatures compromise the physiological health of sea turtles, increasing their vulnerability to various diseases. The link between rising water temperatures and the increased prevalence of Fibropapillomatosis (FP) is a growing concern, particularly in green sea turtles. FP is a debilitating neoplastic disease characterized by the growth of tumors on soft tissues and internal organs, which can impair a turtle’s ability to swim, feed, and see.
The causative agent of FP is Chelonid alphaherpesvirus 5 (ChHV-5), but the expression and severity of the disease are strongly influenced by environmental cofactors. Warmer water temperatures stress the turtle’s immune system, making them less capable of fighting off the viral infection and suppressing the growth of tumors.
Research has demonstrated that tumor growth is more evident during the warmer months of the year, and high disease prevalence is often found in warmer climates and nutrient-rich, degraded coastal habitats. This suggests that climate-related warming acts as a major environmental trigger, facilitating the proliferation and severity of this widespread disease.