Cancún News - The beaches of the Mexican Caribbean face an unprecedented threat this summer as sargassum threatens Mexican Caribbean tourism, washing ashore in massive amounts. The seaweed covers vast stretches of sand and darkens the water. It carries a strong, unpleasant odor that deters visitors. Summer vacations are underway, but many tourists face cancellations or cut their stays short. Esteban Jesús Amaro Mauricio, director of the Sargassum…