Swarms of Chinese vessels have dumped human waste and wastewater for years in a disputed area of the South China Sea, causing algae blooms that have damaged coral reefs and threatened fish in an unfolding catastrophe, a U.S.-based expert said Monday. Satellite images over the last five years show how human waste, sewage and wastewater have accumulated and caused algae in a cluster of reefs in the Spratlys region where hundreds of Chinese fishing ships have anchored in batches, said Liz Derr, who heads Simularity Inc., a software company creating artificial intelligence technologies for satellite imagery analysis.