The humble oyster has proven remarkably effective in protecting one of Bangladesh’s most vulnerable islands from fast-rising seas. Nothing could have prepared Mohammed Shah Nawaz Chowdhury for the sobering reality of Kutubdia Island. The island, off the coast of southern Bangladesh, was rapidly eroding into the sea, causing both land and life to retreat. Many packed up and moved. Those who couldn’t, stayed — inching back, as the island they had called home for generations changed around them. “These were families I had gotten to know, trust and respect,” he says. “It regularly moved me to tears.” Chowdhury was witnessing Bangladesh’s climate migration, caused by sea level rise linked to climate change. By 2050, up to 13.3 million Bangladeshis may become displaced due to climate change. Yet, just off Kutubdia Island’s shore, a glimmer of hope is visible amid the waves. Jutting out of the water, oyster-encrusted reefs glisten in the sun. These reefs are vibrant homes for marine life, a potential source of income for local people and, Chowdhury hopes, they could become a formidable force to defend Kutubdia Island from sea level rise.