When most people hear the word oyster, they think of briny globs of flesh cradled in a half shell, often topped with a dollop of horseradish, a squirt of lemon, a dash of hot sauce and a splash of vodka. Many also think of smooth strands of cream-colored pearls.

But when Ann Birch of the Nature Conservancy — an organization that works globally to “protect ecologically important lands and waters for nature and people,” according to its website — thinks of oysters, she thinks of nature’s version of a Brita water filter, a tasty treat for cod and halibut and other fish that feed on it, and a way to control erosion in Charlotte Harbor and the miles of waterways in Southwest Florida. Birch thinks of a feisty and toiling little creature that can do great things.