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<p>Freshwater ecosystems on tropical islands host unique and functionally important fish communities increasingly threatened by habitat degradation, exotic species, and climate change. Monitoring these systems is challenging due to steep topography, difficult access, and the vulnerability of insular environments. Environmental DNA (eDNA) metabarcoding offers a standardized, non-invasive solution for biodiversity assessment. Here, we applied eDNA metabarcoding with high-throughput sequencing to characterize freshwater fish communities on two contrasting islands in the western Indian Ocean: Mayotte and La Réunion. Four watersheds per island were sampled during two transitional hydrological periods to evaluate inter- and intra-island variability and temporal stability. In total, 49 fish species were detected, spanning freshwater, diadromous, and marine-associated taxa, only eight species were shared between islands, revealing strong biogeographic differentiation. Mayotte was dominated by marine-associated taxa (50%), whereas La Réunion hosted more diadromous (44%) and exotic species (26%) and displayed greater functional richness (FRic = 7.2). Functional traits revealed contrasting ecological strategies: communities in La Réunion showed broad trophic diversity and high trait dispersion, while those in Mayotte were dominated by a few predator species, indicating reduced redundancy and resilience. Spatial structuring was significant in La Réunion, following an upstream–downstream gradient, but absent in Mayotte. No significant temporal variation was observed between sampling campaigns, underscoring the temporal robustness of eDNA detections. Overall, eDNA metabarcoding effectively captured both taxonomic and functional biodiversity patterns, demonstrating its value as a reliable and reproducible tool for standardized biomonitoring and conservation of tropical freshwater ecosystems.</p>

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Taxonomic and functional differentiation of freshwater fish communities in Western Indian Ocean islands: implications for eDNA-based biomonitoring

  • 期刊论文

  • 发表日期：

    2026年1月5日

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  • Jannel LA,
  • Jourand P,
  • Chabanet P,
  • Valade P

摘要

Freshwater ecosystems on tropical islands host unique and functionally important fish communities increasingly threatened by habitat degradation, exotic species, and climate change. Monitoring these systems is challenging due to steep topography, difficult access, and the vulnerability of insular environments. Environmental DNA (eDNA) metabarcoding offers a standardized, non-invasive solution for biodiversity assessment. Here, we applied eDNA metabarcoding with high-throughput sequencing to characterize freshwater fish communities on two contrasting islands in the western Indian Ocean: Mayotte and La Réunion. Four watersheds per island were sampled during two transitional hydrological periods to evaluate inter- and intra-island variability and temporal stability. In total, 49 fish species were detected, spanning freshwater, diadromous, and marine-associated taxa, only eight species were shared between islands, revealing strong biogeographic differentiation. Mayotte was dominated by marine-associated taxa (50%), whereas La Réunion hosted more diadromous (44%) and exotic species (26%) and displayed greater functional richness (FRic = 7.2). Functional traits revealed contrasting ecological strategies: communities in La Réunion showed broad trophic diversity and high trait dispersion, while those in Mayotte were dominated by a few predator species, indicating reduced redundancy and resilience. Spatial structuring was significant in La Réunion, following an upstream–downstream gradient, but absent in Mayotte. No significant temporal variation was observed between sampling campaigns, underscoring the temporal robustness of eDNA detections. Overall, eDNA metabarcoding effectively captured both taxonomic and functional biodiversity patterns, demonstrating its value as a reliable and reproducible tool for standardized biomonitoring and conservation of tropical freshwater ecosystems.