There are three sorts of longevities of protected areas in the State of California. The oldest ones—and there are only about four of those that were created back in the 1990s—have been around for quite a while. The next were a series of no-take marine reserves around the northern Channel Islands off the coast of Santa Barbara. Those were created prior to the statewide network of protected areas. The statewide network is the youngest protected areas of those three categories.
It it takes a while for the consequences of protection to be manifest—you have to wait for individual species to grow up and increase in number—but where it's been examined in the northern Channel Islands, there have been impressive responses by species within the protected areas. Importantly, what you see in those protected areas are increases in the amount of fish biomass—the number and the size of the fish combined—both inside and outside the protected areas, but the increase is much greater within the protected areas.