LONDON, Reuters The U.S. has agreed to forgive 35 million of Indonesian debt over the next nine years, the U.S. Treasury said on Monday, in return for the Southeast Asian country restoring and preserving coral reefs in what experts estimate is the world39;s most biodiverse patch of ocean.

Coral reefs are under increasing threat globally, due largely to climate change which is raising sea temperatures. Data in May showed nearly twothirds have been subjected over the past year to heat stress bad enough to trigger bleaching, which can wipe them out.

The agreement is the fourth debtfornature swap the two countries have struck since 2009 and is expected to fund at least 15 years of conservation work in two key areas of what is known as the 39;Coral Triangle39;.

The Bird39;s Head Seascape and Lesser SundaBanda Seascape it targets both span hundreds of thousands of hectares, a habitat for over three quarters of all coral species and more than 3,000 types of fish, turtles, sharks, whales and dolphins.

Indonesia has roughly 5.1 million hectares of coral reefs, 18 of the world39;s total according to the country39;s tourism ministry, but this year39;s bleaching problems have already had a devastating impact.

These two regions are both at the epicentre of biodiversity, said Alexandre Portnoi, a legal advisor with Conservation International who helped organise the deal.

Indonesia benefitted from earlier debt swaps with the U.S. in 2009, 2011 and 2014 that collectively over…