Oysters were a commercially important species in Chesapeake bay as far back as the 14th century. Now, centuries of over-exploitation have left the Chesapeake devoid of the rich oyster reefs that once existed there, and consequently altered the ecosystem making conditions difficult for many other species - including commercially harvested ones. This is not just because oysters are part of the food chain. They are also ecosystem engineers.
Not only do oyster reefs provide a hard substrate for many other species to live on and around, but they are tenacious filter feeders, cleaning up the water of the bay. It makes sense to instigate oyster restoration projects, not just to provide food, but also to reverse the degradation of the ecosystem.
Unfortunately it is not always that simple, especially where conditions have degraded so dramatically that oysters may simply no longer be able to thrive in areas they once inhabited.
A recent study by Professor Waldbusser and colleagues suggests that one reason for degradation - ocean acidification - can also be buffered by oyster reefs. The idea is simple. Acidic waters mean oyster shells 'dissolve' and as they do so, release an alkaline salt that buffers the acidity levels. The problem today is that there aren't that many dead oyster shells left in the Chesapeake because when we harvest them, most of the shells aren't returned to the bay, and the buffer is heavily reduced.
For those with access to the journal 'Ecology', the original paper can be found here http://dx.doi.org/10.1890/12-1179.1