Marine protected areas (MPAs) in the South Pacific have a long history. In a recent article led by Patrick Smallhorn-West and published in Biodiversity and Conservation, we reviewed what is currently known about the impacts of MPAs in this region. Impact evaluation involves quantifying the effects of an intervention over and above the counterfactual of no intervention or a different intervention. However, determining the true impact of an MPA can be challenging because additional factors beyond the presence of an MPA can confound the observed results. These factors include differences in ecological or socioeconomic conditions between MPA and control sites.

Our semi-structured literature search and synthesis of MPA evaluation studies from the South Pacific was designed to determine: (i) the overall ecological and socioeconomic impacts of MPAs in the region, (ii) what factors were associated with positive, neutral, or negative impacts, and (iii) to what extent the MPA evaluation literature from the region has incorporated counterfactual thinking and robust impact evaluation techniques.

Based on 52 identified studies, 42% of measured ecological impacts were positive. While 72% of socioeconomic impacts were positive, these were from only eight studies. The proportion of positive impacts was comparable between community-based and centrally governed MPAs, suggesting that both governance approaches are viable options in the region. No-take MPAs had a greater number of positive ecological impacts than periodic closures and there was little evidence of any long-term ecological recovery within periodic closures following harvesting.

Importantly, more than half (59%) of the studies examined did not provide any clear consideration of factors beyond the presence of the MPA that might have confounded their results. We therefore conclude that counterfactual thinking has yet to be fully embraced in impact evaluation studies in the region.

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