The world's biggest climate philanthropy has given $24.5 million to protect coastal ecosystems as part of a plan to create the planet's first cross-border marine biosphere reserve, its head of nature told Reuters.

The four grants from the Bezos Earth Fund are intended to help local communities and organisations protect key marine areas in Costa Rica, Panama, Colombia, and Ecuador.

The grants form part of a plan to give $1 billion towards the world's goal of protecting 30% of the planet's land and oceans by 2030. As part of the 'Protecting Our Planet Challenge' with 10 other philanthropies, the group of donors is aiming to provide $5 billion over the same period.

To date, the Bezos Earth Fund has deployed nearly $700 million -- and the broader coalition more than $3 billion -- of the total $5 billion.

The biggest of the newly announced grants - $13.85 million - would go to an organisation called Re:wild to help partners create and strengthen coastal reserves and nursery zones for hammerhead sharks, turtles and other marine life.

"It's an incredibly important area for migration of species," the Bezos Earth Fund's head of nature, Cristian Samper, said. "The only way you can protect this place is doing it in a transboundary way."

In two years the four countries had tripled the size of the protected seas to more than 600,000 square kilometres (231,660 square miles) across 10 separate areas, and the aim now was to create a single biosphere reserve, he said.

"That will be the first in the world," Samper said, adding the Fund was also discussing a similar reserve in the Pacific five times the size of the continental United States.

The fund has agreed to spend $100 million helping the Pacific region implement the global biodiversity goal and would announce a second set of grants in 2026.

"In terms of moving the needle towards 30 by 30, this is exactly the sort of work you need to do."

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