Hi - saw your posting. John Harmanson is my great, great grandfather. I did research on the cemetery in 1985. I spoke with the man who owns Hobgood Plantation, formerly Moreau Plantation. He said that the cemetery caved into the Atchafalaya River and the remains washed out to sea. They did save the tombstones in time. I have not found out anything since that time.
Hope that helps!