But how do you keep them alive?

Oysters.  If large areas of the Chesapeake Bay could bring back viable oyster reefs, then the water quality of the Bay would improve markedly.  Nutrient levels would go down.  Phytoplankton levels would go down.  Anoxia would go down, because less phytoplankton would be dying and sinking to the bottom to get decomposed, using up oxygen.  Water clarity would increase.  Seagrass areas would increase because of the increased water clarity.  Fish would be healthier, because there'd be less bad water and toxic algae and bacteria would all get filtered by the industrious oysters.

But the problem is:  disease.  Can they come back fast enough, and not harvested so much, to defeat the diseases that nearly wiped them out?


Oyster disease:  Dermo
"Dermo is caused by a parasite that thrives in above-average water temperatures* and during droughts*. It inhibits growth and reproduction, and causes death in heavily infected oysters."


 * both consequences of climate change, I must note

Oyster disease: MSX

I don't know.  Maybe the oysters that are surviving are the resistant base of a growing population that can survive in the Bay. 

It's going to be a slow-growth process, but maybe there's a chance.