(CNN) — Before the pandemic put a stop to most international travel, each year millions of people flocked to Southeast Asia's white sandy beaches, ancient temples and diverse wildlife.

In some places the crowds became so intense it caused locals, environmentalists and even governments to complain that overtourism was pushing the region's fragile ecosystems to breaking point.

Coral die-offs, vanishing marine life, damaged cultural sites and idyllic islands overflowing with plastic and human waste were all blamed on too many tourists -- and the unchecked development set up to attract and accommodate them.

Then the global coronavirus pandemic struck. Countries went into lockdown. International travel dramatically reduced. And the tourists were largely gone.

For countries like Cambodia, where tourism contributes an estimated 30% of GDP, the effect has been devastating. Asia-Pacific is estimated to lose $34.6 billion due to the pandemic, the Pacific Asia Travel Association (PATA) said.

As travel restrictions lift, countries that rely heavily on tourism will be competing for visitors as they seek to rebuild their economies. The temptation to attract as many tourists as possible could be difficult to resist.

But experts say the global pause on tourism has offered countries an unprecedented opportunity to examine how to rebuild their tourism industries in a way that benefits their economies and also protects the planet.

An example

As one of the most popular destinations in Southeast Asia, the Philippines welcomes millions of tourists each year, many who visit outlying tropical islands for their sandy beaches and clear waters.

In 2018, so many tourists visited Boracay island that President Roderigo Duterte famously said it had been turned into a "cesspool," and ordered it to close for six months for a massive cleanup.

A tourism boom had encouraged unscrupulous operators to prioritize short-term profits over sustainability, said John Paolo R. Rivera, associate director of the Dr. Andrew L. Tan Center for Tourism. As visitor numbers rose, illegal structures were built close to the beach, many with sewage pipes that led straight out to sea.

After a months-long shutdown, the island reopened in October 2018 with new limits on visitor numbers from 19,000 to 6,000 and bans on smoking and drinking alcohol on the beach. Hotels must now be accredited and comply with environmental standards, including proper waste disposal, and the no-build zone has been extended to 30 meters from the shoreline.

While many welcomed the cleaner, quieter island, its closure came at the expense of locals' livelihoods. Some residents claimed their houses and businesses were flattened in "illegal" demolitions and migrant workers were forced to find jobs elsewhere.

Susanne Becken, director of the Griffith Institute for Tourism in Melbourne, said it is a "brutal" move to completely shut down a place as a lot of lives depend on tourism. She said lessons could be learned by gove