America’s top gymnast, Simone Biles, withdrew Friday from two more events, the vault and uneven bars, as Team USA and China are neck-and-neck in the overall medal tally. Caeleb Dressel won another U.S. gold today with a world record-setting 100-meter butterfly while teammate Katie Ledecky captured her third consecutive 800-meter freestyle win. Meanwhile, “zombie urchins” are deforesting Pacific waters.