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.