MIAMI — We already knew South Florida beaches were bracing for a surge of seaweed, but the mass of seaweed looming in the Atlantic Ocean is now officially record-breaking. The Great Atlantic Sargassum Belt — the official name for the collection of floating brown seaweed that sprawls across 5,000 miles from the Gulf of Mexico to the west coast of Africa — contained about 13 million tons of seaweed by the end of March, according to researchers at the University of South Florida’s Optical Oceanography Lab who have been monitoring the sargassum belt via satellite. That’s a new record for this time...