Spanish authorities have scored a major victory in their legal battle to reclaim a half-billion dollars worth of sunken treasure found and recovered by Tampa-based ocean salvager Odyssey Marine Exploration.

A federal court in Tampa this week agreed that Spain holds a significant legal claim on the richest-ever find of gold and silver coins - yet said the case should go to a higher court for ultimate resolution.

The dispute started almost the moment Odyssey located a wreck it code-named the "Black Swan" in the summer of 2007 and shipped hundreds of buckets of coins from the seafloor to a secure site in Florida.

Spanish authorities claim the wreck is the Mercedes, a military vessel traveling from Peru and sunk by British ships in 1804 off Spain, and thus remains the rightful property of the Spanish government. A federal judge in Tampa agreed, despite Odyssey's claims of a legal salvage job.

District Judge Steven Merryday wrote that the case "combines a compelling episode in naval history, ... the intriguing prospect of recovering great wealth lost in connection with international conflict, the objective of respectful and reliable preservation of warships and their occupants and cargo lost at sea, and the troubling question of the plight of both persons and natural resources subject to colonial exploitation."

He judged that the "ineffable truth of this case is that the Mercedes is a naval vessel of Spain and that the wreck of this naval vessel, the vessel's cargo, and any human remains are the natural and legal patrimony of Spain."

Merryday reasoned, however, that any opinion he might render wouldn't prevent an appeal, so he sent the case to the U.S. 11th Circuit Court of Appeals in Atlanta. That thrilled attorneys for Spain, who say there is no claim to Odyssey's "finder's keepers" line of thinking.

"If you're walking in Central Park and find a gold Rolex, that does not mean it became yours," said Jim Goold, a lawyer who represents the Spanish government in the case. "Same thing with this case. You cannot go find a sunken U.S. Navy ship, take the captain's wedding ring and sell it on eBay."

In two other recent treasure cases where salvagers found Spanish warships and claimed the haul, U.S. courts ultimately granted possession to Spain, he said.

Merryday's ruling does not mean any treasure will go to Spain right away.

The case involves complex treaties, admiralty and international salvage law, partly over whether the vessel was a warship carrying noncommercial property at the time it sank.

Odyssey officials say they expected a lengthy back-and-forth.

"It was clear that this case would go to appeal no matter which way the judge ruled," said Greg Stemm, Odyssey's chief executive, noting that the case does not affect current Odyssey operations and that the company has not been counting on revenue from the so-called "Black Swan" treasure.

Other Odyssey officials have said they would not be surprised if the case ultimately moves to the U.S. Supreme Court.

Meanwhile, Odyssey has been working on more straightforward ocean engineering projects and negotiating deals in advance with foreign governments, including the United Kingdom, about how to handle any treasure.