Green Sea Turtle

The Green Sea Turtle (Chelonia mydas) is a magnificent marine reptile, widely recognized by its smooth, heart-shaped carapace and gentle demeanor. Despite its name, the shell is typically olive to brown, with the "green" referring to the color of its body fat, a result of its herbivorous diet. These turtles can reach up to 1.5 meters (5 feet) in length and are a cherished sight at many dive sites globally, including Norman Reef, Manta Point Nusa Penida, Karang Makassar (Manta Point), Shotgun (The Cauldron), Golden Passage, Tatawa Besar, Siaba Besar, Cannibal Rock, and Yellow Wall of Texas, where they are commonly observed.

Underwater Encounter Behavior

Green Sea Turtles are often encountered by divers in shallow coastal habitats, such as seagrass beds and coral reefs, where they forage or rest. They are generally calm and may appear uninterested in divers, continuing their natural activities while observed from a respectful distance. Divers should approach slowly and cautiously, avoiding sudden movements that might startle them. It is crucial to maintain a respectful distance, as harassing, chasing, disturbing, feeding, or touching these endangered animals is illegal and harmful. If a turtle turns its shell towards a diver, it can be a sign of fear, indicating a need for more space. Green turtles are known to rest on the seafloor, often at depths of 7–26.5 m, for extended periods. Shorter dives are typically associated with active behaviors like swimming or feeding. They must surface to breathe, as they are reptiles with lungs.

Feeding Habits

Adult Green Sea Turtles are unique among sea turtles for being primarily herbivorous, feeding almost exclusively on seagrasses and algae. Their finely serrated jaws are well-adapted for scraping algae off rocks and tearing seagrasses and seaweeds. Divers may observe them grazing in extensive seagrass meadows or on algal-covered reefs. While adults are herbivores, juvenile green turtles have a more omnivorous diet, consuming invertebrates such as jellyfish, sponges, small fish, crustaceans, and worms, gradually shifting to a plant-based diet as they mature. This diet is responsible for the greenish color of their fat and cartilage.

Social Structure

Green Sea Turtles are generally considered solitary animals, though they may occasionally congregate in areas with abundant food sources like seagrass beds. During the breeding season, males and females gather near nesting beaches for mating. While most encounters in unstructured areas are with solitary individuals, more interactive encounters, including inspection behaviors and sometimes body contact, have been observed in deeper, structured habitats like reefs or rock ledges, which serve as important refuge and resting areas. These deeper habitats also facilitate self- and symbiotic cleaning to remove epibionts from their carapaces.

Notable Seasonal Patterns

Green Sea Turtles undertake extensive migrations, often traveling hundreds to thousands of kilometers between their coastal foraging grounds and nesting beaches. Females exhibit strong natal homing, returning to nest on beaches in the general area where they hatched decades earlier. Mating occurs offshore, near the nesting beaches, during the reproductive season.

• Nesting Season: Female green turtles come ashore to lay eggs on sandy beaches, typically at night. In many regions, such as the southeastern United States, nesting occurs in the summer, generally between June and September, with peak activity in June and July. Females lay multiple clutches, averaging around 110–115 eggs per nest, at approximately two-week intervals over several months before returning to their foraging grounds. A female will typically nest every 2 to 5 years.
• Hatching: Eggs incubate for about two months (45-75 days) before hatchlings emerge, usually at night, and make their perilous journey to the sea.
• Migration: After nesting, females migrate back to their foraging grounds, which can be over a thousand kilometers away. Juveniles spend several years in pelagic (open ocean) habitats before moving to nearshore coastal foraging grounds.

Divers visiting dive sites known for Green Sea Turtles, especially those listed as common or abundant (e.g., Siaba Besar, Norman Reef, Manta Point Nusa Penida), have a high chance of encountering these majestic creatures, particularly in areas rich in seagrass or algae.

Green sea turtles are widely distributed across the globe, inhabiting tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean Sea. Their habitat use varies significantly throughout their life stages. Following emergence from nests, hatchlings embark on a journey to offshore pelagic, or open ocean, environments, where they reside for several years, often associated with convergence zones. As they grow into juveniles, they transition from the open ocean to more sheltered, shallow coastal foraging grounds.

Adult green sea turtles primarily frequent shallow coastal waters, including expansive lagoons, bays, and estuaries, particularly areas rich in seagrass beds. These lush underwater meadows serve as crucial feeding grounds. While they largely remain in these shallower areas, green sea turtles are capable of diving to depths exceeding 50 meters (165 feet). Beyond foraging areas, they also utilize deeper, structurally complex habitats such as coral reefs and rocky ledges, which provide vital resting sites. Females undertake extensive migrations to specific oceanic beaches, known as natal beaches, for nesting.

Adult green sea turtles are almost exclusively herbivorous, distinguishing them as the only sea turtle species to maintain a strictly plant-based diet after reaching maturity. Their primary sustenance comes from grazing on seagrasses and algae, a feeding behavior facilitated by their finely serrated jaws. This grazing activity is vital for maintaining the health and growth of seagrass ecosystems. In contrast, juvenile green turtles exhibit an omnivorous diet, consuming a wider variety of prey including worms, young crustaceans, aquatic insects, jellyfish, and fish eggs, alongside plant matter, before transitioning to their adult herbivorous lifestyle.

These turtles are renowned for their highly migratory nature, undertaking arduous journeys, sometimes thousands of miles across oceans, between their feeding grounds and distinct nesting beaches. Females typically return to the very beaches where they were born every two to five years to lay their clutches of eggs. Their navigational prowess is remarkable, believed to be aided by their sensitivity to the Earth's magnetic fields and wave propagation direction.

Historically considered solitary, recent research suggests green sea turtles possess a greater capacity for social interactions than previously understood. They have been observed engaging in consistent, passive interactions and demonstrating tolerance towards other turtles, particularly during foraging. In some instances, group resting and cleaning behaviors have been documented in structured habitats. However, when resources such as food, space, or mates are limited, agonistic behaviors like chasing, jaw snapping, biting, and raking with the beak can occur, especially among adult males during mating and nesting seasons. Despite this, interactions with divers often reveal a calm and gentle demeanor, making them a favored sight for underwater enthusiasts. Green sea turtles have a long lifespan, often living 80 years or more in the wild.