Highlights
- Rapid and standardized assessment of tropical seagrass ecological state.
- Multimetric index combining structure and vitality indicators.
- Spatial mapping of seagrass fragmentation and degradation.
- Links between habitat condition, environment, and megafauna.
- A practical tool for coastal monitoring and impact mitigation.
Abstract
Seagrass meadows are key coastal ecosystems supporting biodiversity, carbon storage, and essential trophic functions, yet they are increasingly threatened by anthropogenic and climatic pressures. Based on the Seagrass Meadows Rapid Assessment Method (SEARAM), a standardized protocol grounded in seagrass biodiversity indicators (SBIs), we developed a reliable and operational index to assess seagrass ecological state at high spatial resolution. Using 536 circular plots and 144 faunal stations across three intertidal reef habitats in Mayotte (Western Indian Ocean), SEARAM integrates structural and vitality sub-indices into a composite seagrass ecological state index (SESI), spatialized by geostatistical interpolation and analyzed using ANOVA, PCA, and multiple regression models. Results revealed highly fragmented meadows dominated by Halodule uninervis and Halophila ovalis, with low canopy height (5 ± 2 cm) and substantial epiphyte loads (37 ± 17%). The inner fringing reef flat showed the poorest ecological state (SESI = 4.8 ± 0.7/10), whereas the barrier reef (5.4 ± 0.8/10) and exposed fringing reef flat (5.6 ± 0.8/10) exhibited moderate scores. Key environmental drivers (turbidity, grain size, pH), significantly explained spatial patterns of seagrass structure and vitality, confirming the influence of sediment and light regimes. Functional relationships were also demonstrated between seagrass condition and associated fauna, particularly green turtle density and dugong feeding traces. SEARAM proved to be a rapid and robust tool for diagnosing tropical seagrass states. Its multimetric framework connects benthic condition to habitat suitability for megafauna, offering an operational foundation for ecological monitoring, management, and impact mitigation within the Avoid–Reduce–Offset (ARO) doctrine.
Graphical abstract
Pinault M., Broudic L., Wickel J., Nicet J.-B., Kerninon F., Ballorain K., Bajjouk T., Lepeigneul O. & Bergerot B., 2026. Unlocking spatial ecological assessment for tropical seagrass habitats using a new rapid assessment method (SEARAM). Environmental and Sustainability Indicators 32: 101538. doi: 10.1016/j.indic.2026.101538. Article.
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