Mapping monumental corals through citizen science

Coral reefs are under unprecedented global threats from multiple stressors. The recent fourth global coral bleaching event triggered mass mortality in most reefs, highlighting the gravity of the situation. Although most corals cannot survive the conditions associated with this kind of event, being generally highly vulnerable to environmental stress, some colonies exhibit exceptional longevity. Such colonies, which have survived enough to reach remarkable sizes comparable, on a biological scale, to those of monumental trees, show a unique resilience. Studying such giant colonies is therefore likely to yield invaluable biological, ecological, and paleoclimatic information. Still, there is limited knowledge on their abundance and distribution due to their relative rarity. To fill this gap, we have launched "Map the Giants", a citizen science research initiative aimed at engaging the public in reporting coral colonies exceeding five meters in linear length. During the first year, the project received over a hundred reports from 14 countries. Most of these were of Porites species and included colonies between 5 and 26 m (median 6.5 m) in linear length. Here, we report the 1-year results of the project, which highlight the potential of citizen science to uncover rare ecological data while fostering public engagement. In doing that, we also provide extensive arguments supporting the importance of preserving these ancient corals, which may hold keys to resilience against global climate change.