Green sea turtles (Chelonia mydas) are marine reptiles inhabiting tropical and subtropical waters. They play a significant role in marine ecosystems, particularly in maintaining the health of seagrass beds. Climate change is impacting green sea turtles in various profound ways, influencing their reproductive success, altering their ocean habitats and food sources, and increasing their susceptibility to health issues.
Reproduction and Nesting Impacts
Rising temperatures significantly affect green sea turtle reproduction through Temperature-Dependent Sex Determination (TDSD). The sex of a sea turtle hatchling is not determined by genetics but by the temperature of the sand during incubation. Warmer sand temperatures, typically above 29.1 degrees Celsius (84.4 degrees Fahrenheit), produce female hatchlings, while cooler temperatures result in males. As global temperatures increase, nesting beaches are becoming warmer, leading to a disproportionate number of female hatchlings. In some regions, like the northern Great Barrier Reef, this skew, with female hatchlings outnumbering males by as much as 116 to 1, poses a long-term threat to the species’ ability to reproduce.
Beyond sex ratios, increasing sand temperatures also directly impact hatchling survival and emergence. Elevated heat can cause eggs to desiccate or overheat, reducing their viability and reducing hatch rates. High temperatures can accelerate development, causing hatchlings to emerge prematurely or during the hottest parts of the day, increasing their risk of dehydration and predation. This reduces the number of hatchlings that successfully reach the ocean.
Coastal nesting habitats are also vulnerable to climate change, specifically sea level rise and increased storm intensity. Rising sea levels submerge and erode sandy shores where turtles lay their eggs, destroying nesting sites. More frequent and intense storms can wash away nests, flood incubating eggs, and further erode the beaches. This loss of suitable nesting grounds forces turtles to compete for remaining areas or abandon traditional sites, contributing to reduced reproductive success and population decline.
Ocean Habitat and Food Source Alterations
Climate change profoundly impacts marine habitats and food sources of green sea turtles. Ocean acidification, from increased carbon dioxide absorption by the oceans, reduces seawater pH. This acidity can degrade crucial ecosystems like seagrass beds, which form the main diet for adult green sea turtles. The health and abundance of these vital foraging grounds are compromised, potentially leading to nutritional stress for the turtles and impacting their overall health and reproductive success.
Warming ocean temperatures and altered ocean currents disrupt the availability and distribution of green sea turtle food sources. Seagrass is sensitive to temperature changes, and prolonged heat stress can impact its growth and density. Changes in currents can shift the location of food resources, forcing turtles to expend more energy on foraging or to move to new, less suitable, areas. This disruption impacts the turtles’ metabolic rates and overall fitness.
Climate change also influences the broader marine food web and habitats that green sea turtles rely on for shelter and foraging. Coral reefs, which provide shelter and indirect food sources, are highly susceptible to warming waters and ocean acidification, leading to coral bleaching and degradation. While green sea turtles primarily eat seagrass, the decline of coral reefs impacts the ecosystem balance, potentially reducing overall biodiversity and affecting other organisms within the turtles’ habitat. Altered currents and ocean temperatures can also disrupt the turtles’ long-distance migration routes between feeding and nesting grounds, making these journeys more challenging and energy-intensive.
Health Vulnerabilities and Population Changes
The cumulative stresses stemming from changing temperatures, habitat degradation, and altered food sources significantly weaken green sea turtles’ immune systems, making them more susceptible to diseases. One notable example is fibropapillomatosis, a debilitating disease characterized by the growth of tumors on the soft tissues and internal organs of turtles. While the exact causes are complex, environmental stressors, including those exacerbated by climate change, are thought to play a role in making turtles more vulnerable to this condition. A compromised immune system leaves turtles less able to fight off pathogens and parasites, contributing to increased morbidity and mortality rates.
These impacts also contribute to shifts in the geographic distribution of green sea turtles. As their traditional habitats become less hospitable due to rising temperatures or habitat loss, turtles may attempt to migrate to new areas in search of more suitable conditions. Such shifts can disrupt migratory pathways and expose turtles to new threats or unfamiliar environments. However, alternative suitable habitats are limited, and these movements may not always be successful.
Ultimately, from skewed sex ratios and degraded nesting sites to compromised food sources and increased disease susceptibility, contribute to population declines. The long-term viability of green sea turtle populations is directly threatened by these environmental changes. With fewer males being born, reduced nesting success, and weakened health, the species faces hurdles in maintaining healthy and reproductively active populations.