A seasonal oil sheen near Destin, Florida.  (U.S. Coast Guard photo by Petty Officer 2nd Class Joshua Ronkowski) NEW ORLEANS – The Coast Guard and Florida’s Department of Environmental Protection (DEP) continue to monitor periodic discharges of oil from the Liberty Ship Thomas Heyward, a World War II era vessel sunk in 1977 to serve as an artificial reef approximately six miles southwest of Destin,...