Evaluating the biological effectiveness of fully and partially protected marine areas

Background: Marine Protected Areas (MPAs) encompass a range of protection levels, from fully protected no-take areas to restriction of only particular activities, gear types, user groups, target species or extraction periods. We synthesized the results of empirical studies that compared partially protected areas (PPA) to (i) no-take marine reserves (NTR) and (ii) to open access areas (Open), to assess the potential benefits of different levels of protection for fish and invertebrate populations. Methods: A systematic search for relevant articles used terms describing MPAs, the biota (e.g. fish, invertebrates) and measures (e.g. density, biomass) of interest. Articles were examined for relevance using specified inclusion criteria. Included articles were appraised critically; the influence of studies whose effect of protection was identified to be confounded by habitat was examined by running a sensitivity analysis parallel to the main analysis that included all studies. Random effect meta-analysis on ln-transformed response ratios was used to examine the response to protection. Subgroup analyses and meta-regression were used to explore variation in effectiveness in relation to MPA and species covariates. Results: Synthesis of available evidence suggests that while PPAs resulted in higher values of biological metrics (density and biomass) than unprotected areas, greatest benefits were apparent in NTR areas when NTRs and PPAs were compared. For fish, the positive response to protection, whether full or partial protection, was primarily driven by targeted fish species. Although positive benefits were also apparent in non-target fish species, the results were more variable, perhaps because of fewer studies focusing on this group. Invertebrate studies were underrepresented and those available focused mainly on scallops, lobsters and sea urchins. Among the targeted species groups, benefits from partial protection relative to fished areas were highest for scallops, whereas benefits from full relative to partial protection were highest for lobsters. The examination of fish and invertebrate response to protection in terms of species richness and length was hampered by small sample sizes. There was significant variability in the magnitude of response to protection among the MPAs included in this study. The factors determining such variation were generally unclear although the size and protection regime of the PPA explained some of this variability. Conclusions: The available evidence suggests that no-take reserves provide some benefit over less protected areas, nevertheless the significant ecological effects of partially protected areas relative to open access areas suggest that partially protected areas are a valuable spatial management tool particularly in areas where exclusion of all extractive activities is not a socio-economically and politically viable option.