Potential protection effects in a small marine reserve: a demersal community analysis from stereo baited remote underwater video

Abstract

Monitoring is essential for efficient management of marine protected areas (MPAs) but often limited financially. Using low-cost stereo baited remote underwater video, we evaluated potential protection effects in the demersal assemblage of a marine reserve in European Atlantic temperate waters (southwestern Portugal). Due to a lack of before-MPA data, we compared multiple sites from the reserve inside and outside, investigated time trends, and assessed the potentially confounding effects of physical habitat. We found greater biomass of the legal-sized group (i.e. commercial above legal minimum landing size) inside the reserve than outside in the most recent year as opposed to the first year and a significant time increase in its abundance and biomass inside but not outside, indicating different trends in protection levels. On the contrary, biomass of the non-target group decreased significantly in both protection levels through time. One of the most targeted species, the legal-sized Diplodus sargus, reached significantly higher biomass inside than outside while also manifesting positive protection signs in abundance and length. Two legal-sized taxa showed no (Diplodus vulgaris) and negative (Mugilidae) protection responses, possibly due to low value and mobility of the latter. We detected positive responses in non-target wrasses Labrus bergylta and Symphodus spp., highlighting incidental fishing interest. Habitat did not interfere with protection effects. We suggest that community analysis based on stereo measurements renders sensitive protection indicators and offers a more thorough approach than prevailing abundance-focused analysis. The proposed low-cost monitoring solution can serve as a model to other MPAs.