Belon Oysters In Boston Harbor?

[ralph124c]

I was walking along a beach at low tide, and saw an interesting looking shell I picked it up…later, I saw several more. It looked like a scallop shell, but had one of the shells almost flat. After searching on the Internet, I found these shells are those of a French oyster (Belon):Ostrea edulis - Wikipedia
How could these have wound up in Boston Harbor?

[lisiate]

Your cite answers your question:

Naturally viable populations have appeared in eastern North America from Maine to Rhode Island subsequent to artificial introduction in the 1940s and 1950s.