As legend goes, the tiny Pacific island nation Palau began with a giant clam.

In the empty sea, the clam grew — bigger and bigger — until it sired Latmikaik, the mother of human children, who created them with the help of storms and ocean currents.

That founding myth still echoes in how Palauans relate to giant clams today. The animals remain woven into daily life and culture and play an outsized role in keeping the country's reefs healthy.

It's easy to see how these massive mollusks inspired a creation story. Giant clams can grow dense shells up to 4.5 feet wide and weigh more than 500 pounds. They are so large, that fish and crabs find safe haven from predators in the folds of their mantles, while coral and sponges routinely grow on their shells. As they breathe, they draw in seawater, filtering out pollution washed into the ocean from the land.

For generations, Palauans have harvested the clams to feed their families.…