Networks of marine protected areas (MPAs) are being increasingly implemented worldwide as conservation management tools. We report here on MPA effectiveness using a 16-year long ROV monitoring program spanning 24 MPAs across California’s MPA network. Our estimates show that MPA protection has a positive effect on the abundance of four demersal fish species with wide geographic distributions across the MPA network. We also demonstrate that there have been regional recoveries in abundance for these species outside of the MPAs. Our approach highlights the utility of remotely operated vehicles (ROVs) to support timely reporting on the effectiveness of MPA networks with quality monitoring data.

Global climate change is driving the redistribution of marine species and thereby potentially restructuring endemic communities. Understanding whether conservation measures can confer resilience to ecosystems is therefore a management priority. Here, we utilise a time-series of benthic imagery to examine the resilience of a no-take marine reserve (NTR) to the establishment of barrens habitat formed by a range extending urchin species. We find evidence for a strong reserve effect, with a doubling in the odds of presence of barrens outside the NTR. However, we find a concerning trajectory of increasing barrens cover in both the reference areas and the NTR over time. Thus, whereas the reserve is demonstrating resistance to the establishment of barrens, there is currently no evidence of recovery. Continuation of the current monitoring program is required to assess whether the NTR can provide long term protection from a catastrophic phase shift and to inform adaptive management.