Marine iguanas, unique to the Galápagos Islands, are the world’s only lizards that have adapted to a marine environment, foraging for algae in the ocean. These reptiles exhibit physiological and behavioral adaptations, such as specialized glands to excrete excess salt and dark coloration for efficient heat absorption. Their life cycle, especially their reproductive habits, is closely tied to the specific environmental conditions of the archipelago.
Identifying Prime Nesting Grounds
Female marine iguanas carefully select their nesting sites, which are typically found on sandy beaches or in areas with volcanic ash. These locations must be situated above the high tide line to prevent the nests from being inundated by seawater. The chosen ground needs to be soft and diggable, allowing the female to excavate a suitable burrow for her eggs.
Nesting sites are often found inland, sometimes as far as 300 meters from the coast. These areas also require sufficient sun exposure, as the warmth of the sun is essential for the incubation of the eggs. The primary requirement remains open, sun-drenched sand or ash for thermal regulation of the nest.
The Egg-Laying Process
Once a suitable nesting ground is identified, the female marine iguana begins the process of digging her burrow. She uses her front and hind legs to excavate a chamber, creating a nest that can range in depth from 30 to 80 centimeters. This digging requires significant energy expenditure.
After the burrow is prepared, the female deposits her clutch of eggs. Marine iguanas typically lay between one and six eggs, with two or three eggs being the most common number. Each leathery white egg measures approximately 9 cm by 4.5 cm and weighs between 80 to 120 grams. After laying eggs, the female covers the nest with sand, camouflaging it from predators.
Incubation and Hatchling Emergence
After the eggs are laid and covered, the female marine iguana’s parental duties are largely complete. She may guard the nest for a few days to deter predators, but eventually she leaves the eggs to incubate on their own. The eggs rely on the warmth of the sun and the surrounding substrate for their development.
The incubation period for marine iguana eggs typically lasts between 90 and 120 days. When the hatchlings are ready, they use an egg tooth to break free from their shells. They then dig their way out of the nest and emerge onto the surface of the sand.
Upon emergence, hatchlings are immediately independent. They run towards rocky areas near the water, seeking shelter and camouflage from predators. The early life of marine iguana hatchlings is challenging, as they face threats from native predators like Galápagos hawks and snakes, as well as introduced species such as cats, rats, and dogs.