Studies of no-take marine reserves: methods for differentiating reserve and habitat effects

No-take marine reserves (NTMRs) are promoted extensively as conservation and fisheries management tools in response to marine ecosystem degradation and fisheries decline, but their use remains controversial. Numerous studies indicate that NTMRs result in higher abundances of fishery-targeted marine species, but few studies utilised robust sampling designs. Comparisons of NTMRs and fished sites must account for potential confounding of habitat type and quality in heterogeneous marine environments. In a review of 164 NTMR studies, many studies failed to adequately account for habitat effects, with no apparent improvement in the literature through time (1983–2013). Five methods employed to partition reserve and habitat effects were used in conjunction with three basic sampling designs: single-point-in-time comparisons, temporal monitoring, and before-after-control-impact (BACI) studies. Researchers evaluating NTMRs: a) ignored habitat or described sites as broadly similar (28.7%); b) constrained sampling to similar habitats (43.9%); c) explicitly tested for habitat differences among sites (12.8%); d) used statistical methods to partition habitat and reserve effects (26.2%); and e) examined changes in habitat caused by reserve protection (17.1%). Over half of the studies (54.3%) made no statistical attempt to account for habitat effects. Robust studies, utilising methods (c-e) within BACI designs, are needed to accurately differentiate NTMR from habitat effects and permit managers to more accurately assess the benefits of NTMRs