Sea turtles are ancient, migratory marine reptiles that have navigated the world’s oceans for over 100 million years. They are an important part of marine ecosystems, contributing to the health of coral reefs and seagrass beds. They have a complex life cycle spanning many decades. Understanding this life cycle is important for their survival and conservation.
From Egg to Hatchling
A sea turtle’s life begins when a female returns to a nesting beach, often returning to the same general area where she was born. Arriving at night, she uses her front flippers to dig a body pit, then her hind flippers to excavate a deeper, vase-shaped egg chamber. Into this chamber, she deposits a clutch of soft-shelled eggs, which can range from 50 to 200 depending on the species. After laying, the female covers the eggs with sand, camouflaging the nest before returning to the sea.
The eggs then undergo an incubation period, which lasts 45 to 70 days (around 60 days) depending on the species and sand temperature. During this period, the sand temperature surrounding the nest determines the sex of the developing hatchlings, a phenomenon known as temperature-dependent sex determination (TSD). Cooler temperatures, below 27.7°C (81.86°F), produce male hatchlings, while warmer temperatures, above 31°C (88.8°F), result in females. A temperature, around 29°C (84.2°F), yields a more balanced ratio of males and females.
Once fully developed, hatchlings use a temporary egg tooth to break free from their shells and then collectively dig their way to the sand surface. This emergence occurs at night to avoid predators and extreme heat. Guided instinctively by the brighter horizon over the ocean, the tiny hatchlings make a dash across the beach to the water.
The Journey to Adulthood
After reaching the ocean, young sea turtles enter a phase called the “lost years,” as tracking their movements in the vast open ocean has historically been challenging. During this oceanic phase, hatchlings are carried by ocean currents, finding refuge and sustenance within floating mats of Sargassum seaweed. These seaweed beds provide both shelter from predators and a rich source of food, including small marine organisms. Recent research, however, indicates that these young turtles are not merely drifting but actively swimming and making decisions about their movements.
As they grow, their diet shifts. Hatchlings start with a carnivorous diet of worms, small crustaceans, and jellyfish, while juveniles become omnivores, consuming a wider range of plant and animal material. This rapid growth during their juvenile stage aids survival. After several years in the open ocean, ranging from one to ten years, sub-adults begin to migrate from pelagic (open ocean) habitats to more coastal foraging grounds. They continue to grow and develop in these nearshore areas, eventually taking on characteristics more similar to adult turtles.
Reproduction and Lifespan
Sea turtles reach sexual maturity after many years, with the exact age varying significantly among species and even populations. Leatherbacks mature as early as 7 to 13 years, while ridleys mature between 11 and 16 years. Hawksbills reach maturity from 20 to 25 years, loggerheads from 25 to 35 years, and green sea turtles take 26 to 40 years. This long maturation period highlights their slow life history.
Mating occurs in coastal waters near nesting grounds, several weeks before the nesting season. Male sea turtles use enlarged claws on their front flippers to grasp the female’s shell during copulation, which takes place in the water. Females mate with multiple males and store sperm for extended periods, allowing for the fertilization of several clutches of eggs within a single nesting season.
Female sea turtles migrate to their natal nesting beaches every two to four years. They lay multiple clutches of eggs in a season, between two and seven, with approximately 10 to 15 days between each clutch. Unlike females, adult male sea turtles remain at sea throughout their lives and do not come ashore. Sea turtles exhibit longevity; many species live for 50 to 100 years or more. This cycle of migration, reproduction, and nesting ensures the perpetuation of these ancient mariners.