Impact evaluation and conservation outcomes in marine protected areas: A case study of the Great Barrier Reef Marine Park
While marine protected areas are being expanded to meet international conservation targets and protect biodiversity from increasing anthropogenic threats, our understanding of the conservation impact of such interventions is limited. Hailed as a success globally, the rezoning of Australia's Great Barrier Reef Marine Park in 2004 was complex and controversial. Despite substantial research within the Marine park, little rigorous evaluation has been undertaken of the rezoning's biological impact - the difference increased protection has made to biodiversity relative to that expected without protection. We review available data of measures of biological impact from ‘new’ no-take zones established in the rezoning and those established under previous zoning. We found 48 studies reporting 782 measures of impact based on comparisons of biological indicators in no-take zones with fished areas. Overwhelmingly, impacts were neutral (57%) or positive (33%). Few data supported causal relationships between new no-take zones and improvements in biological indicators (48 of 159 impacts). The probability of a positive impact increased with time from establishment of no-take zones. Limited conclusions can be drawn from other data. We evaluated whether these measures of impact were robust based on analysis of six key principles of impact evaluation. Sampling was not designed to support causal inferences. Biological monitoring and evaluation designs were limited in providing evidence of the impact of protection. Improved methods that include credible counterfactual data can address limitations of current practice. We highlight ways of progressing impact evaluation techniques to support causal inferences of the impact of marine protected areas generally.