Mémoire

Abstract

Reef fish communities are shifting their distributions in response to global warming, often migrating toward cooler regions. These migrations can lead to taxonomic and functional reorganizations of communities. While functional diversity metrics are commonly used to detect ecological responses in coral reef fish, few studies have examined spatiotemporal dynamics over broad scales. We analyzed long-term fish survey data conducted in 13 localities within 10 marine protected areas (MPAs) across four subregions of the Eastern Tropical Pacific (ETP), covering the period from 2005 to 2023. Using reef fish abundance data paired with ecological and behavioral trait information, we calculated taxonomic (species richness) and functional diversity (functional richness: FRic, evenness: FEve, dispersion: FDis, and originality: FOri). We evaluated their temporal and spatial variation at the regional scale using generalized linear mixed models (GLMMs) in four subregions and localities within subregions. We assessed the influence of oceanographic and anthropogenic variables on these metrics with the use of GLMMs. We highlighted weak indices variations patterns within subregions. Overall, the ETP region is experiencing stagnation or slight but significant decreases in species richness, FRic, FDis, and FOri, with a stagnation in FEve, indicating subtle shifts in reef fish community structure. Surprisingly, we found that FRic was the only index influenced by oceanographic drivers, and that only FDis index was affected by the anthropogenic variable (fishing pressure). We also found that highly protected MPAs exhibited stagnation or slight increases compared to less protected MPAs. This suggests that reef fish communities might be more impacted by local rather than regional factors. These results highlight the importance of local scale long-term monitoring and functional diversity approaches to perceive signs of ecological change under environmental and human impacts.