The Clinch River in Southwest Virginia is one of the oldest rivers in the world. And it’s home to 50 different mussel species. But many of them are endangered. Bruce Cahoon and his students may have recently found a clue about what’s causing the die offs. And: Virginia’s marshes are so thick and tough, hardly anything eats them. Except for purple crabs. They eat the grass and the root, leaving behind nothing but a muddy wasteland. David Johnson says armies of these purple crabs are decimating salt marshes up and down the east coast of the United States.

Later in the show: Virginia’s bay scallops virtually went extinct in the 1930’s. The culprit? A disease that killed off their natural habitat of seagrass. But Chris Patrick and Richard Snyder have recently brought them back from the brink of collapse. Plus: Cholera is no joke. It causes extreme diarrhea in humans and can be deadly within hours. Alison Burke studies what she calls the “cousin of cholera.” It’s a bacteria like cholera found in warm waters that lives and spreads in oysters. She’s looking to use a special kind of virus called a bacteriophage to decontaminate oysters before they wind up on our plates.