Four amateur naturalists and underwater photographers established sixty first records and discovered three species probably new to science at Reunion Island (Indian Ocean) between January 2010 and January 2016, although the marine environment of this island has been studied for some forty years by professional scientists. These results were achieved after snorkeling in coastal areas at a maximum depth of 2 m. All records were validated by professional experts of the relevant groups, with appropriate reservations for photograph-based identifications. The analysis of the methodology used by this group of reef observers highlights three central elements: individual initiative, regular random-path snorkeling practice by local observers, and availability of correspondent observers with sufficient naturalist skills to select accurate data and manage an optimal link with professional scientists. Such achievement emphasizes the efficiency of a citizen- based approach aimed at creating or improving local fauna inventories and discovering new species. Considering that ecological data can be collected during observers' random-path snorkeling sessions, such a project is also of interest for local conservationists and marine ecosystems managers. We therefore recommend the inclusion of these practices in the process of designing standardised observation programs aimed at non-professionals everywhere snorkeling can be practiced, especially in under-studied regions.N
