Résumé
Reunion Island’s coral reefs host complex biological communities, making comprehensive monitoring essential for detecting shifts in species presence as markers of reef health. Biodiversity monitoring, traditionally based upon visual censuses, can be enhanced through environmental DNA (eDNA) surveys that expand species detection. A recent eDNA metabarcoding study used 12S, 18S, and COI gene markers to screen water samples from four back-reef depressions (or ‘lagoons’) in Reunion, revealing distinctive communities across five different sites. This study offers new insight by identifying species and families driving community distinctiveness, and providing a preliminary glimpse into how single time-point eDNA data align with multi-year observational surveys from the Global Coral Reef Monitoring Network (GCRMN) in evaluating its effectiveness for detecting local fish species. The 12S marker detected 52 fish families across all sites, while COI and 18S, targeting mainly invertebrates, identified 262 and 414 families, respectively. Further analyses revealed strong contrasts among all sites, including two within the same lagoon. At the Planch’Alizé site, analyses indicated lower sequence read representation of corals, hydrozoans and several coral-associated fish species. Spatially proximate GCRMN surveys, aggregated over several years, recorded 149 fish species, compared to 213 detected by eDNA. Further, the GCRMN dataset recorded higher proportions of herbivores and omnivores, while eDNA detected a higher proportion of piscivores and captured more nocturnal and/or cryptic species. These results highlight the strength of eDNA for revealing fine-scale community differences while underscoring the importance of combining different survey types to gain a more comprehensive understanding of reef systems to support long term monitoring efforts.
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•Site habitat conditions were reflected through eDNA detection of local animal fauna•Spatially near GCRMN and eDNA surveys recorded 149 and 213 fish species, respectively•GCRMN captured more herbivores and omnivores fish species•eDNA captured more nocturnal and cryptic fish species•Different survey types are necessary for comprehensive understanding of coral reefs