I address the emergence, governance, and effects of marine reserve efforts in the Gulf of California, Mexico, emphasizing a community-based marine reserve network established by the commercial diving sector of Puerto Peñasco, Sonora. This network emerged as a means to manage benthic resources in rocky reefs, primarily rock scallop (Spondylus calcifer) and black murex snail (Hexaplex nigritus). My study also provides an analysis of growth, reproductive ecology, and management of both species.I show that local cooperation to manage fisheries commons incorporating the use of marine reserves can emerge rapidly. Furthermore, this cooperation can be sustained in a fishery spanning no more than two generations, effectively avoiding a local "tragedy of the commons". A blend of social group characteristics, fishers' ecological knowledge and participation in monitoring, and relatively rapid ecological response of the system can play key roles in reinforcing cooperation.I provide evidence of rapid effects of reserves on adjacent fisheries via larvae dispersal. Visual censuses revealed that density of young rock scallop (individuals recruited since reserve establishment) had increased by up to 40.7% within coastal reserves and by 20.6% in fished sites in only two years. Changes were also evident for black murex, with more than a three-fold increase in the density of juveniles within fished sites. These effects, however, were spatially-constricted, evident only for the northern portion of the reserve network. These empirical findings are more indicative of a reserve effect rather than other confounding factors and are consistent with field oceanography data (release of satellite-tracked drifters) and outputs from larvae dispersal models.Finally, I show that just as cooperation can emerge, it can rapidly fall with cascading effects to the system's resilience, particularly amidst threats to social capital and pressure from outside the community. I conclude that even when community-based reserves are effective within the biophysical and local social context, their long-term efficacy will rely on the system's capacity to control access and will demand the institutional capacity to do so. In Mexico this implies, at the least, the government's formal recognition of community-based initiatives and a means to give viability to these efforts.