Two popular coves in the "Calanques" area near Marseille, among southern France's main attractions, saw visitor numbers capped on June 26 for the first time to protect their fragile ecosystem.

The coast between Marseille and Cassis features France's best-known Calanques, age-old rock formations featuring steep cliffs, offering spectacular views, rare marine fauna and protected swimming.

Hugely popular with locals and visitors alike, they are often accessible only by boat or hiking trails. Because the limestone formations have little or no topsoil, plants have had to take root in cracks between the rocks, making their hold tenuous and vulnerable to disturbances.

"The Sugiton and Pierres Tombees calanques have fallen victim to very serious soil erosion because of overcrowding," said the Calanques National Park which manages the landscape of narrow vertical cliffs, inlets and beaches.

"This phenomenon is threatening the landscapes that we love so much, and biodiversity," it said.

Access to Sugiton and Pierres Tombees was limited to 400 people each on Sunday, compared to the usual summer daily visitor numbers of 2,500.

The new measure is to allow "the natural regeneration" of the cove, Nicolas Chardin, the national park's interim director, told AFP at the Sugiton beach.

Online bookings are free of charge, but anyone found at the beaches without a pass on capped days can be fined 68 euros.

"Everything went well this morning, let's hope it stays that way the entire season," Mathieu Benquet, who heads the national park's police team, told AFP.

However, many people - including several foreigners - had been turned away at the several checkpoints along the access path to the cove because they didn't have the required QR code.

Some visitors, hoping for a cooling swim on a hot day, were unhappy about the new rule.

"We've been coming here for 10 years, it feels like our home cove," said Younes Azabib, a 26-year old Marseille resident.

"We thought of everything, the picnic and the pizzas. But we didn't think to book," said his friend, Bilal.

But others appreciated the newfound calmness at the beach.

"This is great," said Isabelle, a 50-year old Marseille resident who usually stays away during the summer because of crowds. "It's finally possible to have a swim."

Nicolas Ponsot, a 41-year-old father of three, also welcomed the visitor cap, saying "it helps to preserve this whole eco-system."

The new rule is to be applied again next Sunday and then daily between July 10 and August 21, the national park said.