Understanding organism-habitat relationships and critically evaluating reference areas is key to marine protected area assessment

Abstract Marine Protected Areas (MPAs) have been implemented globally as a conservation tool to improve the health and function of marine ecosystems. Research has focused on assessing MPA effectiveness, however certain habitats and communities are often avoided because they are difficult or expensive to monitor. Mesophotic (30-100m) rocky reef fish communities are a valuable commercial and recreational resource that is highly targeted but often overlooked in monitoring due to depth restricted sampling. We used two MPAs in California’s statewide protection network, along with parried reference sites, to test how protection status along with environmental conditions influenced the abundance and biomass of three highly targeted species with varying life histories and habitat preferences. Depth and habitat were strong predictors for all groups; ocean whitefish ( Caulolatilus princeps ), California sheephead ( Semicossyphus pulcher ), and targeted rockfish ( Sebastes spp ). The pattern of these effects however, differed between the species groups and the influence of protection was mixed. This work highlights how species with high habitat affinities benefit differently from protection, as a function of depth and habitat representation within the MPA/reference pair. To accurately evaluate MPAs, and the network as a whole, researchers must recognize organism-habitat relationships and incorporate them when assessing conservation efforts.