With season three of The White Lotus drawing new visitors to the already bustling shores of Phuket and Koh Samui, a very different story is unfolding across the Gulf of Thailand.

One day I joined a snorkelling trip to Koh Rang, an island to the west of Koh Mak that is part of the Koh Chang Marine National Park. On the boat I chatted with Rong Rong Zhu, a former research ...