Scientfic American: Massive Porites coral, like the one pictured here, in the Great Barrier Reef are not growing as much anymore, most likely because of warmer and more acidic seawater. The largest coral reef system in the world–and the biggest sign of life on Earth, visible from space–is not growing like it used to. A sampling of 328 massive Porites coral (large structures resembling brains that are formed by tiny polyps) from across the 133,000-square-mile (344,000-square-kilometer) reef reveals that …