The Green Sea Turtle (Chelonia mydas) is a highly migratory species distributed across tropical and subtropical seas worldwide. Adults are primarily herbivorous, feeding almost exclusively on seagrasses and algae. This diet is responsible for the greenish color of their fat, which is the source of their common name, not the color of their shell. These large marine reptiles undertake complex, multi-year cycles, traveling extensively between distant foraging grounds and specific nesting beaches.
Annual Timing and Global Nesting Sites
Green turtle nesting is broadly seasonal, typically commencing in late spring and extending through early fall. Timing varies depending on the latitude and local climate of the nesting site. For instance, peak nesting in the Caribbean often occurs between July and September. Individual females do not nest annually; instead, they usually reproduce on a biennial or triennial cycle, returning to nest only every two to five years.
When a female is ready to reproduce, she embarks on a long-distance migration from her feeding grounds. This journey is driven by natal beach fidelity, compelling her to return to the general region, and often the exact beach, where she herself hatched decades earlier. Major nesting regions include Tortuguero in Costa Rica, Raine Island on Australia’s Great Barrier Reef, and specific beaches in the Caribbean and the Indian Ocean. This fidelity ensures the continuity of distinct turtle populations.
The Overnight Egg-Laying Process
Egg-laying is a solitary and nocturnal event for the green turtle, a behavior that minimizes the risk of overheating and predation. The process begins when the female emerges from the sea, moving above the high-tide line to select a suitable nesting location. Once chosen, she uses her powerful front flippers to excavate a large, shallow depression known as a “body pit.”
After creating the body pit, the female uses her rear flippers to dig a second, flask-shaped egg chamber beneath the center of the pit. The depth of this chamber is determined by the length of her outstretched hind flipper, often reaching up to a meter deep. Into this cavity, the female deposits her clutch of soft-shelled, ping-pong ball-sized eggs. The average clutch size ranges from 80 to 150 eggs.
The female covers the eggs using her hind flippers, compacting the sand tightly to protect the clutch from predators and desiccation. The entire nesting process, from emergence to returning to the sea, can take two hours or more. A female will lay multiple clutches in a single nesting year, returning to the same general beach to deposit between three and seven clutches. The inter-nesting interval is typically 10 to 14 days, allowing time for rest and egg development before she repeats the process.
Incubation and Hatchling Emergence
Once the eggs are laid and covered, the female’s parental duties are complete, and the development of the embryos is left entirely to the environment of the nest. The incubation period is variable, influenced by ambient temperature, but generally ranges from 45 to 75 days. Warmer sand temperatures speed up development, resulting in shorter incubation times, while cooler temperatures slow the process.
Temperature-Dependent Sex Determination (TSD) occurs during the middle third of incubation, where the temperature determines the sex of the hatchlings. Warmer nest temperatures produce a higher proportion of females, while cooler temperatures yield more males. Temperatures above a certain threshold, often around 31°C, can produce nearly all females, while temperatures below a different threshold, around 27.7°C, can produce all males.
After incubation, hatchlings emerge from the nest, synchronized to occur at night. This nocturnal timing offers the young turtles a lower risk of predation and a cooler environment for their dash to the ocean. Emerging hatchlings follow the natural light gradient, typically heading toward the brightest horizon, which is ideally the open sea.