What you want to do first is ID the coins which shouldnt be hard in the What Is It section. Mackaydon can do it. Soaking in saltwater is a great idea for now but I would later switch to distilled water for weeks to try to remove the salts. Ask some others to be certain. After that, I do not know if anything more is needed besides identifying the shipwreck and keeping the location secret. Hopefully you did not take a pic with your phone that has GPS because the location may be imbedded in the picture.