Good news for crab lovers. The population of young Dungeness crabs in San Francisco Bay has sharply increased over the past six years. Experts say the news signals a healthy ocean environment and abundant catches in the future. The number of young crabs from 2000 to 2004 was six times greater than from 1980 to 1999, based on the state records. State wildlife officials and environmentalists are hailing the upward trend after two decades of low numbers.