Green sea turtles ( Chelonia mydas) are large, hard-shelled marine reptiles found throughout tropical and subtropical oceans, inhabiting coastal areas in over 140 countries and nesting in more than 80. These creatures undertake extensive migrations between feeding grounds and nesting beaches. Despite their wide distribution, green sea turtles are classified as an endangered species due to significant population declines. Understanding the threats they face throughout their life cycle is important for their survival.
Vulnerability of Eggs and Hatchlings
The earliest stages of a green sea turtle’s life are exceptionally precarious, starting from the moment eggs are laid on nesting beaches. Nests, buried in the sand, are vulnerable to a variety of terrestrial predators that can dig up and consume the eggs. Common egg predators include raccoons, foxes, feral dogs, and ants.
Upon hatching, typically at night, the small, soft-shelled hatchlings face an immediate gauntlet as they instinctively scramble towards the ocean. They are highly susceptible to predation by ghost crabs and various birds of prey, such as gulls and frigatebirds. Light pollution from coastal development can disorient hatchlings, drawing them away from the sea and making them easier targets.
Challenges for Juvenile Turtles
As green sea turtles grow into juveniles, they transition from open-ocean to nearshore marine environments. While their increased size offers more protection than during the hatchling stage, they remain vulnerable to marine predators. These include several species of sharks, such as reef sharks and bull sharks.
Large predatory fish, including groupers and barracudas, also pose a threat to juvenile turtles. Foraging activities in shallow seagrass beds, a primary food source, can expose them to these dangers. Juveniles spend several years in these habitats before reaching adulthood.
Apex Predators of Adults
Adult green sea turtles, with their robust shells, have few natural predators. Their physical defenses provide protection against most marine life. The primary predators capable of preying on large adults are apex predators within the marine ecosystem.
Tiger sharks are a prominent predator of adult green sea turtles, particularly in regions like Hawaiian waters. These sharks possess specialized teeth adapted to penetrate a turtle’s hard shell. Killer whales (orcas) have also been observed preying on sea turtles.
Anthropogenic Impacts on Survival
Human activities pose pervasive threats to green sea turtles across all life stages. Entanglement in fishing gear, known as bycatch, is a widespread problem, where turtles become trapped in nets or on longlines and can drown. Boat strikes also cause injuries or fatalities, especially in coastal areas with heavy vessel traffic.
Habitat destruction, including the degradation of critical seagrass beds and coastal development on nesting beaches, diminishes essential foraging and breeding grounds. Pollution, particularly plastic, presents a severe hazard; turtles can ingest plastic debris, leading to internal blockages, starvation, or entanglement. Poaching for meat and shells continues to threaten populations in some regions despite protective laws.
Climate change impacts nesting success and hatchling sex ratios. Rising sea levels can inundate nesting beaches, reducing available habitat. Warmer sand temperatures during incubation produce a disproportionate number of female hatchlings, potentially skewing future populations. Extreme heat can also reduce egg viability and survival rates.