Aided by a governor who has promised to preserve the coast, California is expanding its network of areas where fishing and other marine harvesting are banned or restricted. The idea is to better safeguard the diversity and abundance of marine life by limiting those activities in key habitats such as lagoons, bays, kelp forests, rocky reefs and the edges of marine canyons. California already has 80 “marine protected areas” covering about 4 percent of state waters, but scientists agree that most of those sites are too small to help depleted species rebound. “No other state in the Union has done...