WASHINGTON (AP).- The oceans around Australia boast the greatest diversity of sea life on the planet, but the now oil-threatened Gulf of Mexico also ranks in the top five regions for variety of species. And even before the spill, the Gulf was already listed as threatened, according to the latest update of the Census of Marine Life, released Monday. Mark Costello of the Leigh Marine Laboratory, University of Auckland, New Zealand, commented that now it seems the Gulf “is more threatened than we thought it was.” Regions where variety of life is most endangered tended to be the more enclosed seas, such as the Mediterranean, Gulf of Mexico, China’s offshore shelves, Baltic Sea and Caribbean, the new study, done before the oil spill, concluded. “The sea today is in trouble,” said biologist Nancy