Community-wide effects of protection reveal insights into marine protected area effectiveness for reef fish

Abstract

Marine protected areas (MPAs) are not designed the same, nor are they equally effective. Efficacy of MPAs is frequently gauged by measuring the direct ecological responses of fish communities. However measuring the indirect, or knock-on effects from protection can provide additional insight into MPA effectiveness at the community level. Here we applied trait-based and community analyses to investigate MPA effectiveness by evaluating both direct and indirect effects of protection on fish assemblages using baited remote underwater stereo-video data from inside and outside 5 no-take MPAs along the South African coastline. The trait-based analyses indicated the presence of a significant overall direct effect (increased abundance of mature individuals targeted by fisheries) and indirect effects (reduction of the abundance of species not targeted by fisheries) inside MPAs, and highlighted that fish maturity is an essential trait to incorporate when assessing direct effects of protection. However, investigation of the species data of the individual MPAs showed positive reserve effects at the community level (both direct and indirect effects) in only 3 MPAs. For the most part these results conform with current theories on the factors that contribute to MPA effectiveness. Yet, one old, large and isolated no-take MPA showed no direct effects of protection, which is attributed to the lack of adequate offshore reef habitat throughout this MPA. While these results support the value of MPAs as ecosystem management tools, they highlight the need for appropriate site selection when designing MPAs.