Coastal Lights Push Costa Rica’s Turtles From Nesting

Artificial light from hotels, homes, streets and businesses can draw sea turtle hatchlings away from the ocean and deter adult females from nesting on Costa Rica’s beaches. Coastal development doesn’t just change the view after dark; its lights interfere with the conditions turtles need to reach the sea and reproduce.

The built environment takes over the beach

On an undeveloped beach, hatchlings usually head toward the brightest horizon: the night sky above the water. Artificial lights can send them inland, toward roads or private property. The U.S. National Oceanic and Atmospheric Administration says beach lighting can also prevent adult females from coming ashore to lay eggs.

Daniel Arauz, a marine biologist with the Rescue Center for Endangered Marine Species, said coastal building has reduced nesting at Pacific beaches such as Tamarindo and Santa Teresa. He based that assessment on field observations, not a published long-term nest count, and the report says other factors may also play a role. The evidence is specific, but its limits matter: those observations don't establish a measured long-term decline at the beaches.

Sea turtles generally return to nest in the region where they hatched, a behavior called natal philopatry. Still, they aren't exact about the location. Arauz said females will look for another beach if they can't nest where they were born, and may turn back to the water without laying eggs if they sense a threat from light. Heavy noise can have a similar effect.

A Duke University analysis found that fewer green turtles came ashore along the brightest stretches of Tortuguero beach, near the village where artificial light is concentrated. The pattern links a familiar part of coastal infrastructure—lighting—with a measurable difference in where turtles come ashore.

A red-light fix, and its limits

In March 2023, the Costa Rican Electricity Institute installed 71 red-light lamps in Tortuguero. A study of green turtle hatchlings there found that 15% crawled toward artificial light under white lamps, compared with 5% under red light. Those figures show a difference between lighting types; they don't show that red lamps eliminate disorientation.

Some Costa Rican communities have tried dimming lights, including one beach town about two decades ago. Arauz recommends shielding lights, keeping them from pointing at beaches, avoiding large illuminated screens facing the sea, and limiting nighttime noise and disturbance. NOAA and other U.S. wildlife agencies also advise beachfront owners to turn off, shield or redirect lights visible from nesting beaches.

What the beach loses

Turtle nests carry nutrients from the ocean to the sand. Studies in Florida and South Africa found that dune plants and ghost crabs take up nutrients from turtle eggs, while eggs and hatchlings feed birds, crabs and other beach animals. Researchers haven’t measured the impact of losing nesting beaches on Costa Rica’s coastal ecosystems.

Arauz also called for responsible tourism that lets visitors watch turtles without interfering with nesting. At Ostional, known for mass nesting events called arribadas, visitor crowds have previously kept turtles from nesting. Lamps aren't the only source of pressure: people gathered to watch can obstruct the animals, too.

Nesting takes place along both coasts for much of the year, from olive ridley arribadas on the Pacific coast to leatherbacks returning to Caribbean beaches each spring. The recommendations put responsibility on beachfront owners and tourism practices to reduce disturbance. Whether lights are redirected or left to spill across nesting beaches shapes the conditions turtles face there.