One of nature's most spectacular marine events is unfolding on a beach in southern Mexico, where more than 300,000 olive ridley sea turtles have come ashore in a dramatic mass nesting known as an "arribada" — a Spanish word meaning arrival. Thousands of the turtles have surged onto the beach in successive waves, covering the sand in a dense, living carpet as each female digs a nest and deposits her eggs before returning to the sea.

Olive ridley turtles — named for the olive-green colour of their heart-shaped shells — are among the most abundant sea turtle species in the world, yet they remain classified as vulnerable. They are famous for their synchronised mass nesting behaviour, in which enormous numbers of females gather offshore and then come ashore together, typically along a small number of beaches in Mexico, India, and Costa Rica. Mexico's Pacific coastline hosts some of the largest such events recorded anywhere on Earth.

While the scale of the gathering has drawn wonder from conservationists and wildlife observers, the event is unfolding against a troubling backdrop. Hotter and drier conditions linked to climate change are raising serious concerns about hatchling survival. Sea turtle eggs are highly sensitive to temperature: the heat of the sand determines not only whether embryos develop successfully, but also the sex ratio of the hatchlings. Sustained rises in temperature can skew populations heavily female or, in extreme cases, cook eggs entirely before they hatch.

Why this matters: mass nesting events like this one are both a conservation success story and a warning signal. Decades of protection efforts in Mexico — including nest monitoring, limits on beach access during nesting season, and anti-poaching measures — have helped stabilise olive ridley populations along the Pacific coast. But climate change threatens to undo those gains in ways that are difficult to counter through traditional conservation tools alone. Scientists warn that without broader action to limit rising temperatures, beaches that have long served as crucial nesting grounds could become increasingly hostile environments for the next generation of turtles.