UC San Diego

Although it is well established that Marine Protected Areas (MPAs) are effective tools for augmenting the abundance of fished species, effects on biodiversity and community assembly are less clear. Many rockfish species were overfished in the California Current Ecosystem at the turn of the 21st century, and establishment of two large MPAs in the Southern California Bight, the Cowcod Conservation Areas (CCAs), alongside favorable environmental conditions helped rebuild overfished rockfish stock by 2020. Here, we evaluate the impacts of the CCAs and environment on rockfish diversity and assemblage structure using a 16-year time series (1998-2013) of genetically-identified rockfish larvae. We demonstrate that while rockfish richness generically increased across the time series, the greatest increases occurred inside CCAs when temperature was low and dissolved oxygen high. Using multivariate methods (ordination and generalized linear latent variable models), we also find a clear species assemblage shift after the 2001 CCA implementations, driven largely by increased presence/abundance of rockfishes targeted by fisheries. Our results suggest that the large and sustained MPAs along the southern California coast have induced increases in the diversity of rockfish reproductive output, driven largely by the direct effects of fishing cessation on targeted species.