Giant clams, which can grow to weigh more than 200 kilograms (440 pounds), have long been traded for their shells, which are carved into decorative items, as well as for food and the aquarium trade.

You’re in good company if you’ve combed the shoreline for shells, marveled at the glinting, microscopic pieces that make up the sand, or held a snail shell up to your ear listening for the ocean or ...