The oyster (Ostrea edulis) was a staple food for British working-class people in our great-grandparents’ time. Here’s a 19th century recipe for fish and oyster pie. My mother’s and grandmother’s recipe books tell you how to make steak, kidney and oyster pudding. In both of those recipes, the oyster was used to eke out more expensive seafood (cod, haddock) or meat (beef). But the oyster was overfished so badly that it became a luxury.
Now O. edulis might be coming back in British waters. Eivind Burkow at The Coastal House tells us of encouragement to eat more UK oysters.
This is in the context of decreasing ocean pH (that means increasing ocean acidity). The European Project on OCean Acidification (EPOCA) tells us that acidification harms oysters.