Spatial variation in fish assemblages in seagrass habitats in Mauritius across protection levels: A baseline assessment using remote sensing and BRUVS

Seagrass meadows are important coastal habitats that support diverse fish species, yet their ecological role in Mauritius remains poorly understood. This study combined remote sensing and field-based methods to assess seagrass distribution and fish communities across three sites on the east coast of Mauritius with varying levels of protection: two fishing reserves (Poste Lafayette and Roche Noires) and one unprotected site (Palmar). An estimated 185.4 hectares of seagrass was mapped using Sentinel-2 imagery and machine learning, with the greatest extent detected at Roche Noires (111.9 ha), followed by Poste Lafayette (64.1 ha) and Palmar (9.4 ha). Fish assemblages were surveyed using Baited Remote Underwater Video System (BRUVS), with 25 deployments recording 2,035 individuals representing 63 species from 23 families. Observed species richness was higher at the protected sites, although differences among sites were not statistically significant. Fish assemblage composition differed significantly among sites (PERMANOVA, R² = 0.18, p = 0.006), while habitat type exerted a stronger influence on assemblage structure (PERMANOVA, R2 = 0.54, p = 0.001). Non-metric multidimensional scaling (NMDS) showed partial overlap among sites, but clearer separation among habitat types. Thalassodendron ciliatum-dominated habitats supported the most distinct communities, suggesting that the structural complexity of seagrasses influences fish diversity. These findings provide baseline evidence of seagrass extent and associated fish communities in Mauritius and highlight the importance of incorporating habitat characteristics into seagrass conservation, fishing reserve management and marine spatial planning.